Electronics Circuit Schematics, Diagrams and diy Projects

Quality Stereo Wireless Microphone or Audio Link

2010-03-09T17:00:00.004+05:00

This stereo FM wireless microphone also makes a great quality audio link. We tested it to beyond 50 meters and it was rock solid. It’s certainly not the first wireless microphone we’ve ever published but this one is a little different. It’s stereo, providing surprisingly good quality sound. Second, it has a really good range. We tested it at well over 50m and it was still performing very well – noise-free, in fact – but at the time we couldn’t get our receiver any further away. So it’s likely to have even better range than that.

Complete Project:

It's easy to build, requires very little setup... and it's cheap! In fact, the low price might turn some people off, thinking it's low quality. Try it - and be pleasantly surprised!

Third, it really is simple to build – the hard work (the transmitter module) is already done for you. It’s just a matter of assembling the microphone module, which contains the electret mics themselves, preamp and level controls, and soldering the transmitter module onto it, "piggy back" style.

FM Transmitter:

Finally, the transmitter module is crystal-locked, so you won’t have the drift probles of some earlier wireless microphones. And just in case you were wondering, that doesn’t mean the output is locked to one particular frequency – it has a nifty synthesis circuit built in to give you the choice of seven different frequencies between 106.7MHz and 107.7MHz.

On-board preset pots adjust the sensitivity of each channel to take into account mic differences or if you require different levels in each channel.

By the way, the transmitter module is quite capable of operating at line level if you want just a line level transmitter (eg, to feed an audio program around your home). Sensitivity is about 100mV. Oatley Electronics, who designed the kit, have the transmitter module available by itself if that’s what you’re after. But more on that anon.

Parts Layout:

You also have the choice of two power supply levels – 3-6V or 7-15V DC. The latter results in a lower current drain. The transmitter module also has a "5V out" rail to supply power to the preamp module.

Circuit Diagram:

Two electret microphone inserts are supplied in the kit. These can be soldered direct to the PC board to make it a fully self-contained project or they can be attached to the board via suitable lengths of mini shielded coax cable. A third option is to use "proper" microphones – they can be electret or dynamic types – but no provision has been made for plugging these in.

Typical Specifications:

Audio response:.....................20Hz-15kHz.
Channel separation: ........................40dB
Total Harmonic Distortion: ...............0.1%
Output Frequency:...........106.7-107.2MHz
Pre Emphasis: ..................................50μS
DC supply voltage range: ................3-15V
Supply Current: .......................30mA @ 9V

Source: Silicon Chip 28 May 2005

The Itsy-Bitsy USB Lamp

2010-03-04T09:58:00.003+05:00

It plugs into the USB port and is just the shot for checking motherboard switch and jumper settings. Many readers will remember a commercial product of a few years ago, the "Itty Bitty Book Light". It was designed to clip over the top of a book to give just a tiny light on the page when, for example, you were reading in bed and didn't wish to disturb your partner. Times have changed. Now we're all working with computers.

Many's the time I've been trying to look deep inside a computer and wished it was a bit brighter so I could read type numbers, see plug and socket orientations, check board seating, and so on. Sometimes, even a torch won't work because it's too big to get really deep down. You can't get that light where you really need it.

Well, here's the answer. We've called it the Itsy Bitsy USB Lamp. It is such a delightfully simple idea we're wondering why no-one ever thought of it before. It started life (and continues) as a student project at Massey University in Wellington, New Zealand - and in fact was submitted to us by the lecturer, Stan Swan. When we say simple, we mean it: just a USB plug on a suitable length of cable, a super bright white LED and a series resistor to limit LED current. The LED and resistor are housed in an in-line fuse holder (without its innards!) which makes a superb little "wand" and also protects the electronics, such as they are.

The USB Port:

In all modern computers, you will find at least one, usually two and often four USB ports. USB stands for Universal Serial Bus, and is one of the latest incarnations of methods to get information in and out of your computer. We're not particularly interested in information transfer as such. But we are interested in the fact that the USB port offers power to external devices - +5V is available on pin 1 (0V on pin 4). Up to 100mA is available from the USB port - far more than we need for this little application. That's the reason for the series resistor. A 47Ω resistor will limit the current to about 25mA - just about ideal.

The Construction:

The first thing you will need is a USB cable with at least one male plug on it. These are becoming fairly common and you should be able to pick one up for just a few dollars. A local computer shop has a 1m USB extension cable for $6 but you could well do better than this at computer fairs, swap meets, etc. Here's a tip: get together with a mate and buy a male-to-male USB cable. Cut the cable in half and you can both build an Itty Bitty USB Lamp for half the cost!

Strip back about 5cm of the outer insulation and shield from the "bare" end of the USB cable. Normal USB cables have four wires: red, white, black and green (as well as the shield). The green and white carry the data - we don't need them so they can be trimmed right back (make sure the wires inside their insulation are not exposed at all).

Circuit Diagram:

A tiny length of heatshrink tubing over the ends of the green and white wires will ensure that there cannot be shorts, either to themselves, to the shield wire or to the red or black wires. Carefully bare about 2mm of the insulation on the red and black wires. Before we go too much further, open up the in-line 3AG fuse holder and remove the wires and spring inside. All we want are the two plastic bits.

Slide the longer of the two pieces over the end of the wire, smallest end first. (You may need to drill or ream out the hole a little to accommodate the wire but don't go overboard! Similarly, this might be necessary on the other bit of fuseholder to accommodate the LED when we come to it shortly.) The photograph shows this well. Slide the fuseholder down far enough so it is out of the way.

Cut the anode lead (the longer lead) of the bright white LED to about 3mm long. Similarly, cut both leads of a 47Ω 1/4W (or even 1/8W) resistor to about 3mm long and carefully solder one lead of the resistor to the anode of the LED. The 47Ω resistor will have a colour code of yellow, purple, black, gold (or yellow, purple, black, gold, gold if it's a 5-bander).

It can be soldered either way around. Cut a length of spaghetti insulation (or some tiny plastic tubing) long enough to cover the resistor and its leads, then slide this over the resistor so the connection to the anode is completely insulated. Heatshrink tubing may also be used for this purpose, but is not essential.

Cut another two short lengths of insulation (say 5mm) and slide them over the red and black wires of the USB cable. Solder the red wire to the resistor end and the black wire to the LED cathode. By the way, spaghetti insulation is not pasta. Now slide the 5mm lengths of insulation over the solder joints - it is important that the bits cannot short out to each other when scrunched up inside their fuseholder "home". Strictly speaking, this assembly should be fused in case of a short but even it there is a short the USB port will limit the current available. So no fuse! (But it's better not to have a short anyway!).

Testing:

Before going any further, check and check again that everything is as it should be. Most of all, make sure that there is no possibility of any shorts from one lead of the USB cable to another - particularly the green and white (data) wires. (Failure to do this could damage your computer). With your computer on, plug the USB plug into the USB socket. If everything is OK, the white LED should glow brightly. If not, check for shorts or open circuits.

Final assembly:

Slide the fuseholder back up the USB cable, pushing everything inside it until only the LED and abut 3mm of its leads are emerging. Slide the other end of the fuseholder (the shorter end) onto the longer piece so that the LED just pokes the top of its head out the hole (flush with the hole is fine). Twist the fuseholder end onto its body to lock it in place. And that's it. Now when you need a bright light anywhere around your computer - all you have to do is plug it in to the USB port!

Parts List:

1 - USB male plug moulded to suitable length 4-way screened cable
1 - Ultrabright White LED (preferably at least 2000mCd) (eg, DSE Z-3980, 3981, 3982, etc)
1 - 3AG in-line 2-part plastic fuseholder (eg, DSE P-7912, Jaycar SZ-2015, etc).
1 - 47Ω 1/4W or 1/8W resistor
Lengths of thin diameter heatshrink (preferably) or spaghetti insulation

source

USB Power Injector For External Hard Drives

2010-03-03T10:55:00.003+05:00

A portable USB hard drive is a great way to back up data but what if your USB ports are unable to supply enough "juice" to power the drive? A modified version of the Silicon Chip Usb Power Injector is the answer. For some time now, the author has used a portable USB hard drive to back up data at work. As with most such drives, it is powered directly from the USB port, so it doesn’t require an external plug pack supply.

Project's Picture:

In fact, the device is powered from two USB ports, since one port is incapable of supplying sufficient current. That’s done using a special USB cable that’s supplied with the drive. It has two connectors fitted to one end, forming what is basically a "Y" configuration (see photo). One connector is wired for both power and data while the other connector has just the power supply connections. In use, the two connectors are plugged into adjacent USB ports, so that power for the drive is simultaneously sourced from both ports.

USB Cable:

An external USB hard drive is usually powered by plugging two connectors at one end of a special USB cable into adjacent USB ports on the computer. This allows power to be sourced from both ports. According to the USB specification, USB ports are rated to supply up to 500mA at 5V DC, so two connected in parallel should be quite capable of powering a portable USB hard drive – at least in theory.

Complete Project:

Unfortunately, in my case, it didn’t quite work out that way. Although the USB drive worked fine with several work computers, it was a "no-go" on my home machine. Instead, when it was plugged into the front-panel USB ports, the drive repeatedly emitted a distinctive chirping sound as it unsuccessfully tried to spin up. During this process, Windows XP did recognise that a device had been plugged in but that’s as far as it went – it couldn’t identify the device and certainly didn’t recognize the drive.

Plugging the drive into the rear-panel ports gave exactly the same result. The problem wasn’t just confined to this particular drive either. A newly-acquired Maxtor OneTouch4 Mini drive also failed to power up correctly on my home computer, despite working perfectly on several work computers.

Circuit diagram:

The revised USB Power Injector is essentially a switch and a 5V regulator. The Vbus supply from USB socket CON1 turns on transistor Q1 which then turns on power Mosfet Q2. This then feeds a 6V DC regulated supply from an external plug pack to regulator REG1 which in turn supplies 5V to USB socket CON2.

Source: Silicon Chip 26 June 2008

Modular Preamplifier Switching Center

2010-03-03T09:48:00.006+05:00

Four high level inputs, Double Bar switching

This module can be a necessary addition to the Modular Preamplifier Control Center when more than two sources need to be connected to the preamplifier chain. Four high level inputs can be selected by means of SW1 and routed to the output. The output of this module must be connected by a suitable cable to one of the two inputs of the Control Center module. In this way, a total of five inputs will be available to the user of this module combination.

The Switching Control features also the so called "Double Bar", i.e. the possibility of routing to an external unit, e.g. a recorder (tape or digital) an input signal different from that reproduced at the time by the amplifier. For example, you can listen in to a CD whereas the signal coming from a radio station through the Tuner is routed to the recorder. This selection is operated by means of SW2.

As with the other modules of this series, each electronic board can be fitted into a standard enclosure: Hammond extruded aluminum cases are well suited to host the boards of this preamp. In particular, the cases sized 16 x 10.3 x 5.3 cm or 22 x 10.3 x 5.3 cm have a very good look when stacked. See below an example of the possible arrangement of the front and rear panels of this module.

Circuit diagram:

Modular Preamp Switching Center Circuit Diagram

Parts:

R1,R2,R3,R4____100K 1/4W Resistors
R5_____________560R 1/4W Resistor
SW1,SW2________2 poles 4 ways Rotary Switches
J1 to J6_______RCA audio input sockets

Notes:

No power supply is necessary for this module
The circuit diagram shows the Left channel only, so all the parts must be doubled except SW1 and SW2 which are double pole switches, i.e. ready for stereo.

A possible arrangement of the front and rear panels of this Module

Switching Center Front Panel

Switching Center Rear Panel

Automatic Water Tank Filler Circuit Diagram

2010-03-02T19:15:00.001+05:00

This circuit has been very useful in filling a header tank for a reticulated water supply on a farm. Eight troughs are supplied in different paddocks where a lack of water would have serious consequences for the stock. In the past, the tank had been filled daily by a time clock which was not successful. During hot weather, the stock would empty the tank on a regular basis and then be without water for several hours or the tank would overflow and flood the area if the weather was wet and the cattle did not drink much.

Circuit Diagram:

The circuit described has been used to maintain the level of water in the header tank within prescribed limits. It controls a 3HP submersible bore pump which has a high starting current, necessitating a solid-state relay sufficient to take the starting load. Two Darlington transistors, Q1 & Q3, in conjunction with Q2 & Q4, are connected to the upper and lower water sensors in the tank. Q2 & Q4 have a common 5.6kO load resistor and function as a NOR gate. The output of the NOR gate drives Q5 which activates relay RLY1.

Initially, when the water level is low, both sensors will be open-circuit, the NOR gate output will be high and the relay will be turned on. This causes the normally closed (NC) contacts of the relay to open and disconnect the lower sensor. However, the upper sensor will still be open circuit and the NOR gate output will be high, keeping the relay closed. The normally open (NO) contact of the relay will be closed to operate the solid-state relay RLY2 to run the pump.

This state continues until the water reaches the top sensor which will then drop the output from the NOR gate to 0V. The disables relay RLY1 and the pump is stopped. In practice the upper level sensor is just below the overflow from the tank and the lower sensor about half way up the tank. The sensor contacts are simply two stainless steel screws about 25mm apart and screwed through the poly tank walls. The wiring junctions on the side of the tank are protected by neutral-cure silicone sealant.

Digital Remote Thermometer

2010-03-02T01:41:00.002+05:00

Remote sensor sends data via mains supply, Temperature range: 00.0 to 99.9 °C

This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter.

Transmitter circuit operation:

IC1 is a precision centigrade temperature sensor with a linear output of 10mV/°C driving IC2, a voltage-frequency converter. At its output pin (3), an input of 10mV is converted to 100Hz frequency pulses. Thus, for example, a temperature of 20°C is converted by IC1 to 200mV and then by IC2 to 2KHz. Q1 is the driver of the power output transistor Q2, coupled to the mains supply by L1 and C7, C8.

Circuit diagram:

Transmitter Circuit Diagram

Transmitter parts:

R1 = 100K 1/4W Resistors
R2 = 47R 1/4W Resistor
R3 = 100K 1/4W Resistors
R4 = 5K 1/2W Trimmer Cermet
R5 = 12K 1/4W Resistor
R6 = 10K 1/4W Resistor
R7 = 6K8 1/4W Resistor
R8 = 1K 1/4W Resistors
R9 = 1K 1/4W Resistors

C1 = 220nF 63V Polyester Capacitor
C2 = 10nF 63V Polyester Capacitor
C3 = 1µF 63V Polyester Capacitor
C4 = 1nF 63V Polyester Capacitors
C5 = 2n2 63V Polyester Capacitor
C6 = 1nF 63V Polyester Capacitors
C7 = 47nF 400V Polyester Capacitors
C8 = 47nF 400V Polyester Capacitors
C9 = 1000µF 25V Electrolytic Capacitor

D1 = 1N4148 75V 150mA Diode
D2 = 1N4002 100V 1A Diodes
D3 = 1N4002 100V 1A Diodes
D4 = 5mm. Red LED

IC1 = LM35 Linear temperature sensor IC
IC2 = LM331 Voltage-frequency converter IC
IC3 = 78L06 6V 100mA Voltage regulator IC

Q1 = BC238 25V 100mA NPN Transistor
Q2 = BD139 80V 1.5A NPN Transistor
T1 = 220V Primary, 12+12V Secondary 3VA Mains transformer
PL = Male Mains plug & cable
L1 = Primary (Connected to Q2 Collector): 100 turns
Secondary: 10 turns
Wire diameter: O.2mm. enameled
Plastic former with ferrite core. Outer diameter: 4mm.

Receiver circuit operation:

The frequency pulses coming from mains supply and safely insulated by C1, C2 & L1 are amplified by Q1; diodes D1 and D2 limiting peaks at its input. Pulses are filtered by C5, squared by IC1B, divided by 10 in IC2B and sent for the final count to the clock input of IC5. IC4 is the time-base generator: it provides reset pulses for IC1B and IC5 and enables latches and gate-time of IC5 at 1Hz frequency. It is driven by a 5Hz square wave obtained from 50Hz mains frequency picked-up from T1 secondary, squared by IC1C and divided by 10 in IC2A. IC5 drives the displays' cathodes via Q2, Q3 & Q4 at a multiplexing rate frequency fixed by C7. It drives also the 3 displays' paralleled anodes via the BCD-to-7 segment decoder IC6. Summing up, input pulses from mains supply at, say, 2KHz frequency, are divided by 10 and displayed as 20.0°C.

Circuit diagram:

Receiver Circuit Diagram

Receiver Parts:

R1 = 100K 1/4W Resistor
R2 = 1K 1/4W Resistor
R3 = 12K 1/4W Resistors
R4 = 12K 1/4W Resistors
R5 = 47K 1/4W Resistor
R6 = 12K 1/4W Resistors
R8 = 12K 1/4W Resistors
R9-R15=470R 1/4W Resistors
R16 = 680R 1/4W Resistor

C1 = 47nF 400V Polyester Capacitors
C2 = 47nF 400V Polyester Capacitors
C3 = 1nF 63V Polyester Capacitors
C4 = 10nF 63V Polyester Capacitor
C7 = 1nF 63V Polyester Capacitors
C5 = 220nF 63V Polyester Capacitors
C6 = 220nF 63V Polyester Capacitors
C8 = 1000µF 25V Electrolytic Capacitor
C9 = 100pF 63V Ceramic Capacitor
C10 = 220nF 63V Polyester Capacitors

D1 = 1N4148 75V 150mA Diodes
D2 = 1N4148 75V 150mA Diodes
D3 = 1N4002 100V 1A Diodes
D4 = 1N4002 100V 1A Diodes
D5 = 1N4148 75V 150mA Diodes
D6 = Common-cathode 7-segment LED mini-displays
D7 = Common-cathode 7-segment LED mini-displays
D8 = Common-cathode 7-segment LED mini-displays

IC1 = 4093 Quad 2 input Schmitt NAND Gate IC
IC2 = 4518 Dual BCD Up-Counter IC
IC3 = 78L12 12V 100mA Voltage regulator IC
IC4 = 4017 Decade Counter with 10 decoded outputs IC
IC5 = 4553 Three-digit BCD Counter IC
IC6 = 4511 BCD-to-7-Segment Latch/Decoder/Driver IC

Q1 = BC239C 25V 100mA NPN Transistor
Q2 = BC327 45V 800mA PNP Transistors
Q3 = BC327 45V 800mA PNP Transistors
Q4 = BC327 45V 800mA PNP Transistors

PL = Male Mains plug & cable
T1 = 220V Primary, 12+12V Secondary 3VA Mains transformer
L1 = Primary (Connected to C1 & C2): 10 turns
Secondary: 100 turns
Wire diameter: O.2mm. enameled
Plastic former with ferrite core. Outer diameter: 4mm.

Notes:

D6 is the Most Significant Digit and D8 is the Least Significant Digit.
R16 is connected to the Dot anode of D7 to illuminate permanently the decimal point.
Set the ferrite cores of both inductors for maximum output (best measured with an oscilloscope, but not critical).
Set trimmer R4 in the transmitter to obtain a frequency of 5KHz at pin 3 of IC2 with an input of 0.5Vcc at pin 7 (a digital frequency meter is required).
More simple setup: place a thermometer close to IC1 sensor, then set R4 to obtain the same reading of the thermometer in the receiver's display.
Keep the sensor (IC1) well away from heating sources (e.g. Mains Transformer T1).
Linearity is very good.
Warning! Both circuits are connected to 230Vac mains, then some parts in the circuit boards are subjected to lethal potential! Avoid touching the circuits when plugged and enclose them in plastic boxes.

9 Volt 2 Ampere DC Power Supply Circuit Diagram

2010-03-01T20:03:00.005+05:00

A simple 9 Volt 2 amp supply using a single IC regulator.

There is little to be said about this circuit. All the work is done by the regulator. The 7809 can deliver up to 2 amps continuous output whilst maintaining a low noise and very well regulated supply. The circuit will work without the extra components, but for reverse polarity protection a 1N5400 diode (D1) is provided at the input, extra smoothing being provided by C1. The output stage includes C2 for extra filtering, if powering a logic circuit than a 100nF (C3) capacitor is also desirable to remove any high frequency switching noise.

Circuit diagram:

9 Volt 2 amp DC Power Supply Circuit Diagram

Parts:

C1 = 100uF-25V electrolytic capacitor, at least 25V voltage rating
C2 = 10uF-25V electrolytic capacitor, at least 6-16V voltage rating
C3 = 100nF-63V ceramic or polyester capacitor
IC = 7809 Positive Voltage Regulator IC
D1 = 1N5400 Diode

Mobile Phone Travel Charger Circuit Diagram

2010-02-26T10:09:00.005+05:00

Charge Your Mobile Phone While Enjoying The Journey

Here is an ideal Mobile charger using 1.5 volt pen cells to charge mobile phone while traveling. It can replenish cell phone battery three or four times in places where AC power is not available. Most of the Mobile phone batteries are rated at 3.6 V/500 mA. A single pen torch cell can provide 1.5 volts and 1.5 Amps current. So if four pen cells are connected serially, it will form a battery pack with 6 volt and 1.5 Amps current. When power is applied to the circuit through S1, transistor Q1 conducts and Green LED lights.

When Q1 conducts Q2 also conducts since its base becomes negative. Charging current flows from the collector of Q1. To reduce the charging voltage to 4.7 volts, Zener diode D2 is used. The output gives 20 mA current for slow charging. If more current is required for fast charging, reduce the value of R4 to 47 ohms so that 80 mA current will be available. Output points are used to connect the charger with the mobile phone. Use suitable pins for this and connect with correct polarity. The circuit comes from here.

Circuit diagram:

Mobile Phone Travel Charger

Parts:

R1 = 1K
R2 = 470R
R3 = 4.7K
R4 = 270R
R5 = 27R
C1 = 100uF-25V
D1 = Green LED
D2 = 4.7V/1W Zener
B1 = 1.5Vx4 Cells
S1 = On/Off Switch
Q1 = BC548
Q2 = SK100

3-30V 3A Adjustable Regulated DC Power Supply

2010-02-23T19:10:00.003+05:00

A power supply for all general circuits, Based on a stablized DC voltage of 30 volt

This power supply is meant as an auxiliary or as a permanent power supply for all common circuits based on a stabilized DC voltage between 3 and 30V provided that the consumption does not exceed 3A. Of course this power supply unit can also be used for other purposes. Be replacing the trimmer by a potentiometer, it may even be used as an adjustable power supply unit. A good quality heatsink must be used.

Picture of project:

3 TO 30 Volt 3 Ampere DC Power Supply

Circuit diagram:

3 TO 30 Volt 3 Ampere DC Power Supply Circuit Diagram

Parts list:

R1 = 8.2K
R2 = 2.2K
R3 = 680R
R4 = 1K
R5 = 82K
R6 = 0.18R/5W
C1 = 470p
C2 = 100nF-63V
C3 = 100nF-63V
C4 = 100uF-63V
C5 = 10KuF-60V
D1-D6 = 6.6A
Q1 = MJ3001 (Darligton)
IC1 = UA723D

Specifications:

Overload protected
Sshort-circuit stable
Output current: max. 3A
Output ripple voltage: 0.5mV
Output voltage: adjustable from 3 to 30V, stabilized
Input voltage: 9 to 30V AC (depending on the desired output voltage)

Assembling into a housing:

Depending on the transformer used, one may chose one of two housings
If a metal housing is used, it must be earthed for security purposes.
Make sure the cooling body does not touch the housing. This might cause a short circuit.
When mounting a toroidal transformer, it must be seen to that the fixation bolt does not touch the cover. This might cause the burning of the transformer
If the circuit is to be integrated into another housing, it must be provided with ventilation holes (one may make these holes oneself), necessary for the release of the heat developed.

Notes :

Connect a voltage meter to the points ‘GND’ and ‘+OUT’ and adjust ‘RV1’ until the desired output voltage is reached.
Apply some thermo-conducting pasta to the bottom side of the transistor and mount it on the heatsink.
If you need 3-8 volt then R2 will be 5.6K
If you need more than 8 volts then the R2 will be 2.2K
Suitable transformer 30vAC at 120VA

Adjustable 1.3-22V Regulated Power Supply

2010-02-23T15:44:00.003+05:00

Want a regulated voltage that can be adjusted to suit your application? This Adjustable Power Supply is small, easy to build and can be adapted to produce a fully regulated voltage ranging from 1.3V to 22V at currents up to 1A. This circuit come from SiliconChip Magazine

There are many fixed-voltage IC regulators available and these can be had with 5V, 6V 8V, 9V, 12V & 15V outputs. But what if you want a voltage output that does not fit into one of the standard ranges or if you want to be able to easily adjust this output voltage? An adjustable regulator is the answer – one that can be set to provide the exact voltage you require.

This Adjustable Power Supply comprises a small PC board that utilises a 3-terminal regulator. It does not have too many other components – in fact, there are just three diodes, three capacitors, a resistor and a trimpot to set the output voltage from the regulator. The circuit is based on an LM317T adjustable voltage regulator. D1 provides reverse polarity protection while P1 sets the output voltage.

Project looks like:

Picture Of The Project

Parts layout:

Parts Layout Of The Project

PCB layout:

PCB Layout Of The Project

Circuit diagram:

Adjustable Regulated DC Power Supply Circuit Diagram

Parts list:

IC = LM317T adjustable 3-terminal regulator
P1 = 2k horizontal trimpot
R1 = 110R-0.25W
C1 = 100uF-25V
C2 = 10uF-25V
C3 = 100uF-25V
D1 = 1N4004
D2 = 1N4004
D3 = 1N4004

NiCd Battery Charger With Reverse Polarity Protection

2010-02-16T18:27:00.004+05:00

Small and portable unit, Can charge multiple batteries at once

This NiCd battery Charger can charge up to 7 NiCd batteries connected in series. This number can be increased if the power supply is increased with 1.65V for each supplementary battery. If Q2 is mounted on a proper heatsink, the input voltage can be increased at a maximum of 25V. Unlike most of comercial NiCd chargers available on the market, this charger has a reverse polarity protection. Another great quality is that it does not discharge the battery if the charger is disconnected from the power supply.

Usually , NiCd batteries must be charged in 14 hours at a charging current equal with a tenth percent from battery capacity. For example, a 500 mAh is charged at 50 mA for 14 hours. If the charging current is too high this will damage the battery. The level of charging current is controlled with P1 between 0 mA – 1000 mA. Q1 is opened when the NiCd battery is connected with the right polarity or if the output terminals are empty. Q2 must be mounted on a heatsink. If you cannot obtain a BD679, then replace it with any NPN medium power Darlington transistor having the output parameters at 30V and 2A. By lowering R3 value the maximum output current can be increased up to 1A.

Circuit diagram:

NiCd Battery Charger With Reverse Polarity Protection

Parts:

P1 = 1K
R1 = 680R
R2 = 47K
R3 = 1R-3W
Q1 = BC557
Q2 = BD679 (Darlington)
D1-D5 = 1N4148
D6 = 1N4001

NiMh and NiCd Battery Charger Circuit

2010-02-16T15:23:00.005+05:00

This automatic NiCd charger for 9V NiCd batteries is using 555 timer properties and is very easy to build. Why is an automatic 9 volts NiCd battery charger? Because you can leave the battery for charging as much as you like: it will be always completely charged and ready for use when is needed. It wont be overcharged and it will not discharge. With the values presented in the circuit diagram, the battery charger NiCd circuit is suitable for 6V and 9V batteries.

9 volt types with 6 and 7 cells are charging with 20mA; P1 must be adjusted so that the NiCd charger disconnects after 14 hours. Window inferior level is set at 1V below this value with P2. 5V battery type with 4 or 5 cells are charged at 55mA. Again, with P1 adjust the NiCd charger circuit so it disconnects after 14 hours. Window inferior level must be set at 0.8V below this value.

Circuit diagram:

Automatic NiCd Battery Charger Circuit Diagram

Parts:

P1 = 50K
P2 = 50K
R1 = 820R
R2 = 820R
R3 = 1K
R4 = 10K
R5 = 10K
R6 = 100R
D1 = 4.7V Zener
D2 = 1N4001
D4 = 1N4148
D5 = B40C1500 Diode Bridge
C1 = 220uF - 25V
Q1 = BC547B
IC = 555
B1 = 9V Ni-Cad Battery

Automatic Loudness Control Circuit Schematic

2010-02-15T13:10:00.004+05:00

Simple add-on module, Switchable "Control-flat" option

In order to obtain a good audio reproduction at different listening levels, a different tone-controls setting should be necessary to suit the well known behavior of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves.

A simple approach to this problem can be done inserting a circuit in the preamplifier stage, capable of varying automatically the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels.

Fortunately, the human ear is not too critical, so a rather simple circuit can provide a satisfactory performance through a 40dB range. The circuit is shown with SW1 in the "Control-flat" position, i.e. without the Automatic Loudness Control. In this position the circuit acts as a linear preamplifier stage, with the voltage gain set by means of Trimmer R7.

Switching SW1 in the opposite position the circuit becomes an Automatic Loudness Control and its frequency response varies in respect to the position of the control knob by the amount shown in the table below. C1 boosts the low frequencies and C4 boosts the higher ones. Maximum boost at low frequencies is limited by R2; R5 do the same at high frequencies.

Circuit diagram:

Automatic Loudness Controller Circuit Diagram

Parts:

P1_________________10K Linear Potentiometer (Dual-gang for stereo)
R1,R6,R8__________100K 1/4W Resistors
R2_________________27K 1/4W Resistor
R3,R5_______________1K 1/4W Resistors
R4__________________1M 1/4W Resistor
R7_________________20K 1/2W Trimmer Cermet
C1________________100nF 63V Polyester Capacitor
C2_________________47nF 63V Polyester Capacitor
C3________________470nF 63V Polyester Capacitor
C4_________________15nF 63V Polyester Capacitor
C5,C9_______________1µF 63V Electrolytic or Polyester Capacitors
C6,C8______________47µF 63V Electrolytic Capacitors
C7________________100pF 63V Ceramic Capacitor
IC1_______________TL072 Dual BIFET Op-Amp
SW1________________DPDT Switch (four poles for stereo)

Technical data:

Frequency response referred to 1KHz and different control knob positions:

Total harmonic distortion at all frequencies and 1V RMS output: <0.01%

Notes:

SW1 is shown in "Control flat" position.
Schematic shows left channel only, therefore for stereo operation all parts must be doubled except IC1, C6 and C8.
Numbers in parentheses show IC1 right channel pin connections.
R7 should be set to obtain maximum undistorted output power from the amplifier with a standard music program source and P1 rotated fully clockwise. [Link]

USB Powered Mobile Phone Battery Charger

2010-02-15T10:55:00.004+05:00

Now you can charge your Mobile Phone from the USB outlet of PC

This simple circuit can give regulated 4.7 volts for charging a mobile phone. USB outlet can give 5 volts DC at 100mA current which is sufficient for the slow charging of mobile phones. Most of the Mobile Phone batteries are rated 3.6 volts at 1000 to 1300 mAh. These battery packs have 3 NiMh or Lithium cells having 1.2 volt rating. Usually the battery pack requires 4.5 volts at 300-500 mA current for fast charging.

But low current charging is better to increase the efficiency of the battery. The circuit described here provides 4.7 regulated voltage and sufficient current for the slow charging of the mobile phone. Transistor Q1 is used to give the regulated output. Any medium power NPN transistor like CL100, BD139, TIP122 can be used. Zener diode D2 controls the output voltage and D1 protects the polarity of the output supply. Front end of the circuit should be connected to a A type USB plug.

Connect a red wire to pin1 and black wire to pin 4 of the plug for easy polarity identification. Connect the output to a suitable charger pin to connect it with the mobile phone. After assembling the circuit, insert the USB plug into the socket and measure the output from the circuit. If the output is OK and polarity is correct, connect it with the mobile phone.

Circuit diagram:

USB Powered Mobile Phone Charger Circuit Diagram

Parts:

Q1 = BD139
D1 = 1N4001
D2 = 4.7V - 1/2W
R1 = 560R - 1/2W
C1 = 16V - 100uF

Note:

If the polarity is incorrect, it will destroy the mobile battery. So take extreme care.

45 Watt Class-B Audio Power Amplifier

2010-02-12T09:17:00.003+05:00

45W into 8 Ohm - 69W into 4 Ohm, Easy to build - No setup required

These goals were achieved by using a discrete-components op-amp driving a BJT complementary common-emitter output stage into Class B operation. In this way, for small output currents, the output transistors are turned off, and the op-amp provides all of the output current. At higher output currents, the power transistors conduct, and the contribution of the op-amp is limited to approximately 0.7/R11. The quiescent current of the op-amp biases the external transistors, and hence greatly reduces the range of crossover.

The idea sprang up from a letter published on Wireless World, December 1982, page 65 written by N. M. Allinson, then at the University of Keele, Staffordshire. In this letter, op-amp ICs were intended as drivers but, as supply voltages up to +/- 35V are required for an amplifier of about 50W, the use of an op-amp made of discrete-components was then considered and the choice proved rewarding.

The discrete-components op-amp is based on a Douglas Self design. Nevertheless, his circuit featured quite obviously a Class A output stage. As for proper operation of this amplifier a Class B output stage op-amp is required, the original circuit was modified accordingly. Using a mains transformer with a secondary winding rated at the common value of 25 + 25V (or 24 + 24V) and 100/120VA power, two amplifiers can be driven at 45W and 69W output power into 8 and 4 Ohms respectively, with very low distortion (less than 0.01% @ 1kHz and 20W into 8 Ohms).

This simple, straightforward but rugged circuit, though intended for any high quality audio application and, above all, to complete the recently started series of articles forming the Modular Preamplifier Control Center, is also well suited to make a very good Guitar or Bass amplifier. Enjoy!

Circuit diagram:

45W Class-B Amplifier Circuit Diagram

Parts:

R1______________18K - 1/4W Resistor
R2_______________3.9K - 1/4W Resistor
R3,R6____________1K - 1/4W Resistors
R4_______________2.2K - 1/4W Resistor
R5______________15K - 1/4W Resistor
R7______________22K - 1/4W Resistor
R8_____________330R - 1/4W Resistor
R9,R10__________10R - 1/4W Resistors
R11,R12_________47R - 1/4W Resistors
R13_____________10R - 1W Resistor

C1_______________1µF - 63V Polyester Capacitor
C2_____________470pF - 63V Polystyrene or Ceramic Capacitor
C3______________47µF - 25V Electrolytic Capacitor
C4______________15pF - 63V Polystyrene or Ceramic Capacitor
C6_____________220nF - 100V Polyester Capacitor
C6_____________100nF - 63V Polyester Capacitor

D1,D2,D3,D4___1N4148 - 75V 150mA Diodes

Q1,Q2________BC560C - 45V 100mA Low noise High gain PNP Transistors
Q3,Q4________BC556 - 65V 100mA PNP Transistors
Q5___________BC546 - 65V 100mA NPN Transistor
Q6___________BD139 - 80V 1.5A NPN Transistor
Q7___________BD140 - 80V 1.5A PNP Transistor
Q8__________2N3055 - 60V 15A NPN Transistor
Q9__________MJ2955 - 60V 15A PNP Transistor

Power supply :

Power Supply Circuit Diagram

Parts:

R1_______________3.3K - 1/2W Resistor
C1,C2_________4700µF - 50V Electrolytic Capacitors
C3,C4__________100nF - 63V Polyester Capacitors
D1_____________200V 8A Diode bridge
D2_____________5mm. Red LED
F1,F2__________4A Fuses with sockets
T1_____________230V or 115V Primary, 25+25V Secondary 120VA Mains transformer
PL1____________Male Mains plug
SW1____________SPST Mains switch

Comments:

The main design targets for this amplifier were as follows:

Output power in the 40 - 70W range
Simple circuitry
Easy to locate, low cost components
Rugged performance
No setup

Notes:

2N3055 and MJ2955 transistors were listed for Q8 and Q9 as the preferred types, but many different output transistors can be used satisfactorily: TIP3055/TIP2955, TIP35/TIP36, MJ802/MJ4502 amongst others.
Discrete op-amp output transistors Q6 and Q7 do not require any heatsink as their cases remain at ambient temperature. Power transistors Q8 and Q9 should be mounted on a black, finned heatsink as usual.

Technical data:

Output power (1KHz sinewave):

45 Watt RMS into 8 Ohms - 69W RMS into 4 Ohms

Sensitivity:

0.81V RMS input for 45W output

Frequency response @ 1W RMS:

15Hz to 23KHz -0.2dB

Total harmonic distortion @ 1KHz:

1W 0.008% 20W 0.008% 45W 0.016%

Total harmonic distortion @10KHz:

1W 0.01% 20W 0.015% 45W 0.025%

Unconditionally stable on capacitive loads

60 Watt Audio Power Amplifier Circuit Diagram

2010-01-17T12:00:00.002+05:00

High Quality, powerful unit: 90W into 4 Ohm load, Also suited as guitar or bass amplifier

To celebrate the hundredth design posted to this website, and to fulfil the requests of many correspondents wanting an amplifier more powerful than the 25W MosFet, a 60 - 90W High Quality power amplifier design is presented here. Circuit topology is about the same of the above mentioned amplifier, but the extremely rugged IRFP240 and IRFP9240 MosFet devices are used as the output pair, and well renowned high voltage Motorola's transistors are employed in the preceding stages.

The supply rails voltage was kept prudentially at the rather low value of + and - 40V. For those wishing to experiment, the supply rails voltage could be raised to + and - 50V maximum, allowing the amplifier to approach the 100W into 8 Ohm target: enjoy! A matching, discrete components, Modular Preamplifier design is available here: Modular Audio Preamplifier.

Amplifier section:

60 Watt MosFet Audio Power Amplifier Circuit Diagram

Parts:

R1______________47K 1/4W Resistor
R2_______________4K7 1/4W Resistor
R3______________22K 1/4W Resistor
R4_______________1K 1/4W Resistor
R5,R12,R13_____330R 1/4W Resistors
R6_______________1K5 1/4W Resistor
R7______________15K 1/4W Resistor
R8______________33K 1/4W Resistor
R9_____________150K 1/4W Resistor
R10____________500R 1/2W Trimmer Cermet
R11_____________39R 1/4W Resistor
R14,R15_________R33 2.5W Resistors
R16_____________10R 2.5W Resistor
R17_____________R22 5W Resistor (wirewound)
C1_____________470nF 63V Polyester Capacitor
C2_____________470pF 63V Polystyrene or ceramic Capacitor
C3______________47µF 63V Electrolytic Capacitor
C4,C8,C9,C11___100nF 63V Polyester Capacitors
C5______________10pF 63V Polystyrene or ceramic Capacitor
C6_______________1µF 63V Polyester Capacitor
C7,C10_________100µF 63V Electrolytic Capacitors
D1___________1N4002 100V 1A Diode
D2_____________5mm. Red LED
Q1,Q2,Q4_____MPSA43 200V 500mA NPN Transistors
Q3,Q5________BC546 65V 100mA NPN Transistors
Q6___________MJE340 200V 500mA NPN Transistor
Q7___________MJE350 200V 500mA PNP Transistor
Q8___________IRFP240 200V 20A N-Channel Hexfet Transistor
Q9___________IRFP9240 200V 12A P-Channel Hexfet Transistor

Power supply :

60 Watt MosFet Audio Amplifier Power Supply Circuit Diagram

Parts:

R1_______________3K9 1W Resistor
C1,C2_________4700µF 63V Electrolytic Capacitors (See Notes)
C3,C4__________100nF 63V Polyester Capacitors
D1_____________400V 8A Diode bridge
D2_____________5mm. Red LED
F1,F2__________4A Fuses with sockets
T1_____________230V or 115V Primary, 30+30V Secondary 160VA Mains transformer
PL1____________Male Mains plug
SW1____________SPST Mains switch

Notes:

In the original circuit, a three-diode string was wired in series to R10. Two of these diodes are now replaced by a red LED in order to achieve improved quiescent current stability over a larger temperature range. Thanks to David Edwards of LedeAudio for this suggestion.
A small, U-shaped heatsink must be fitted to Q6 & Q7.
Q8 & Q9 must be mounted on large heatsinks.
Quiescent current can be measured by means of an Avo-meter wired in series to the positive supply rail and no input signal.
Set the Trimmer R10 to its minimum resistance.
Power-on the amplifier and adjust R10 to read a current drawing of about 120 - 130mA.
Wait about 15 minutes, watch if the current is varying and readjust if necessary.
The value suggested for C1 and C2 in the Power Supply Parts List is the minimum required for a mono amplifier. For optimum performance and in stereo configurations, this value should be increased: 10000µF is a good compromise.
A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of R1, R3, C2, C3 and C4 and the ground input wire. Connect R7 and C7 to C11 to output ground. Then connect separately the input and output grounds to the power supply ground.

Technical data:

Output power:
60 Watt RMS @ 8 Ohm (1KHz sinewave) - 90W RMS @ 4 Ohm
Sensitivity:
1V RMS input for 58W output
Frequency response:
30Hz to 20KHz -1dB
Total harmonic distortion @ 1KHz:
1W 0.003% 10W 0.006% 20W 0.01% 40W 0.013% 60W 0.018%
Total harmonic distortion @10KHz:
1W 0.005% 10W 0.02% 20W 0.03% 40W 0.06% 60W 0.09%
Unconditionally stable on capacitive loads

Components Voltage Tester Circuit Schematic

2010-01-17T11:58:00.003+05:00

This simple circuit tests speakers, microphones, transformers and voltage. It's basically a very low frequency oscillator that produces extremely short 'fruity' pulses. The type of sound produced is very easy to hear and to determine the precise direction it is coming from, thus making it ideal for checking the phasing in multiple speaker installations. It is also very useful for car stereo installations as well as public address systems where it can drive dozens of speakers directly on a 100V or 70V line system.

The signal is also easy to hear on a public address system so that you can drive around a large installation with the window down and easily hear each speaker as you drive past. It is easy to check that a speaker is in phase with its neighbours, by listening for the artificial centre created between two identical sound sources. Q1 and Q2 oscillate when connected to loads between zero and about 1000O. The frequency increases as the resistance of the load increases - 8O loads produce about 8Hz output while 100O loads will produce about 100Hz output, although it is only approximate.

The unit is also useful for checking dynamic microphones (not condenser types), headphones, transformers (both audio and mains) and resistance loads (only visual checks via the LED). The pulses produced can sound too loud for some delicate circuits such as dynamic microphones and headphones, but the pulse is so short that it is virtually impossible to do any damage; the average current flow is only a few milliamps.

The circuit needs no power switch as the oscillator only operates when the negative side of the battery is connected through the load being tested. The LED flashes at each pulse as a visual indication that the load is lower than about 1000O. The circuit works from a 3V battery pack. To use a 9V battery change the 15O resistor to 47O, the 1.8O resistor to 5.6O and the .033µF capacitor to .01µF. LED2, diode D3, zener diode ZD1 and the series 220O resistor form a voltage indicator which is used to detect and indicate any voltage greater than about 10V.

LED2 only illuminates if the voltage rises above the threshold set by ZD1 and D1, which is more than the battery voltage (3V or 9V). These components can be omitted if the device is not going to be used for working on cars. However, it's quite handy having a device that can check power wires, shorts to chassis and speakers in a car.

Circuit diagram:

Components Voltage Tester Circuit Diagram

Parts:

R1 = 5.6M
R2 = 1.8R
R3 = 15R
R4 = 220R
Q1 = BC327
Q2 = BC337
D1 = Green LED
D2 = Red LED
D3 = 1N4148
Z1 = 6.8V Zener
C1 = 0.033uF
B1 = 3V Battery

Amplifier Timer Circuit Schematic

2010-01-17T11:54:00.002+05:00

Turns-off your amplifier when idle for 15 minutes, Fed by amplifier tape-output

This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting.

Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.

Circuit diagram:

Amplifier Timer Circuit Diagram

Parts:

R1,R8___________1K 1/4W Resistors
R2,R3___________4K7 1/4W Resistors
R4_____________22K 1/4W Resistor
R5______________4M7 1/4W Resistor
R6,R9__________10K 1/4W Resistors
R7______________1M5 1/4W Resistor
R10___________100K 1/4W Resistor
R11____________15K 1/4W Resistor
R12____________10M 1/4W Resistor
R13_____________1M 1/4W Resistor
R14_____________8K2 1/4W Resistor
R15_____________1K8 1/4W Resistor
C1____________470µF 25V Electrolytic Capacitor
C2,C3,C6______100nF 63V Polyester Capacitors
C4,C5__________10µF 25V Electrolytic Capacitors
D1_____Diode bridge 100V 1A
D2,D7________1N4002 100V 1A Diodes
D3__________Red LED 5mm.
D4_______Yellow LED 5mm.
D5,D6________1N4148 75V 150mA Diodes
IC1___________78L12 12V 100mA Voltage regulator IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________4060 14 stage ripple counter and oscillator IC
Q1____________BC557 45V 100mA PNP Transistor
Q2____________BC337 45V 800mA NPN Transistor
J1______________RCA audio input socket
P1_____________SPST Mains suited Pushbutton
P2_____________SPST Pushbutton
T1_____________220V Primary, 12V Secondary 3VA Mains transformer
RL1___________10.5V 270 Ohm Relay with SPST 5A 220V switch
PL1____________Male Mains plug
SK1__________Female Mains socket

Notes:

Simply connect left or right channel tape output of your amplifier to J1.
You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.
The delay time can be varied changing R13 and/or C6 values.
Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.

18W + 18W Stereo Hi-Fi Audio Amplifier (TDA2030)

2010-01-07T09:44:00.003+05:00

2 x 18W Hi-Fi Stereo Power Amplifier based around two TDA2030 ICs. It has good input sensitivity, low distortion, good operating stability and full protection against overloads and output short-circuits. It can be used as a booster amplifier for existing small systems or to drive a second pair of speakers besides the ones already connected to the system. The board needs a symmetrical power supply of ±18Vdc/3A and can be connected to loads of 8 or 4 Ohm. Large heat sink is required for this circuit. Diagram shown below indicates only left channel. Make two circuits for for stereo version.

Picture of the project:

18+18 Watt Hi-Fi Stereo Audio Amplifier Circuit Diagram

Circuit Diagram:

Diagram Shows Only One Channel

Parts:

R1 = 22K
R2 = 680R
R3 = 22K
R4 = 1R-1w
D1 = 1N4001
D2 = 1N4001
C1 = 1uf-25V
C2 = 22uF-25V
C3 = 100nF-63V
C4 = 100nF-63V
C5 = 100uF-25V
C6 = 100uF-25V
C7 = 220nF-63V
IC = TDA2030

If it does not work:

Check your work for possible dry joints, bridges across adjacent tracks or soldering flux residues that usually cause problems.
Check again all the external connections to and from the circuit to see if there is a mistake there.
See that there are no components missing or inserted in the wrong places.
Make sure that all the polarized components have been soldered the right way round.
Make sure the supply has the correct voltage and is connected the right way round to your circuit.
Check your project for faulty or damaged components.

Technical Specifications:

Supply voltage = ±18Vdc/3A symmetrical (see text)
Current consumption = 3A maximum
Input impedance = 500K Ohms
Input sensitivity = 250 mV
Signal to noise ratio = 80 dB
Frequency response = 20 - 20,000 Hz ± 1 dB
Distortion = 0.5 % maximum
Load impedance = 4 - 8 ohm

Dual Relay Driver Board Circuit Schematic

2010-01-04T13:48:00.002+05:00

A simple and convenient way to interface 2 relays for switching application in your project. This relay driver boosts the input impedance with a regular BC547 NPN transistor (or equivalent). Very common driver. It can drive a variety of relays, including a reed-relay. Transistor Q1and Q2 are a simple common-emitter amplifier that increases the effective sensitivity of the 12 volt relay coil about a 100 times, or in other words, the current gain for this circuit is 100. Using this setup reduces the relay sensitivity to a few volts. R3 and R4 restricts the input current to Q1 and Q2 to a safe limit. Diodes D3 and D4 are EMF dampers and filter off any sparking when the relay
de-energizes.

Picture of the project:

Front View Of Dual Channel Relay Board Driver

Circuit diagram:

2 Channel Relay Driver Circuit Diagram

Parts:

R1-R2 = 1K
R3-R4 = 5.6K
C1-C2 = 100nF-63V
D1-D2 = Red LED
D3-D4 = 1N4001
L1-L2 = 12V Relay
Q1-Q2 = BC547

Specification:

Input - 12 VDC @ 84 mA
Output - two SPDT relay
Relay specification - 5 A @ 230 VAC
Trigger level-2~5VDC
Berg pins for connecting power and trigger voltage
LED on each channel indicates relay status

One second Audible Clock Circuit Schematic

2010-01-04T13:18:00.002+05:00

Accurate, finger-operated portable unit, 3 - 12V Battery supply

This accurate one-pulse-per-second clock is made with a few common parts and driven from a 50 or 60 Hertz mains supply but with no direct connection to it. A beep or metronome-like click and/or a visible flash, will beat the one-second time and can be useful in many applications in which some sort of time-delay counting in seconds is desirable. The circuit is formed by a CMos 4024 counter/divider chip and 3 diodes, arranged to divide the frequency of the input signal at pin #1 by 50 (or 60, see Notes).

The input impedance at pin #1 is very hight, so simply touching the pin (or a short track or piece of wire connected to it) is usually enough to provide the necessary input signal. Another way to provide an input signal consists in a piece of wire wrapped several times around any convenient mains cable or transformer. No other connection is necessary.

Circuit diagram:

One second Audible Clock Circuit Diagram

Parts:

R1 = 10K
R2 = 47.K
R3 = 100R
C1 = 1nF-63V
C2 = 10µF-25V
C3 = 100nF-63V
D1 = 1N4148
D2 = 1N4148
D3 = 1N4148
D4 = LED-(Optional, any shape and color, see Notes)
D5 = 1N4148-75V 150mA Diode (Optional, see Notes)
Q1 = BC337-45V 800mA NPN Transistor
IC1 = 4024-7 stage ripple counter IC
BZ1 = Piezo sounder (incorporating 3KHz oscillator)
SPKR = 8 Ohm, 40 - 50mm diameter Loudspeaker (Optional, see Notes)
SW1 = SPST Toggle or Slide Switch (Optional, see Notes)
B1 = 3 to 12V Battery (See Notes)

Notes:

To allow precise circuit operation in places where the mains supply frequency is rated at 60Hz, the circuit must be modified as follows: disconnect the Cathode of D1 from pin #11 of IC1 and connect it to pin #9. Add a further 1N4148 diode, connecting its Anode to R1 and the Cathode to pin #6 of IC1: that's all!
The circuit will work fine with battery voltages in the 3 -12V range.
The visual display, formed by D4 and R3 is optional. Please note that R3 value shown in the Parts list is suited to low battery voltages. If 9V or higher voltages are used, change its value to 1K.
If a metronome-like click is needed, R2 and BZ1 must be omitted and substituted by the circuit shown enclosed in dashed lines, right-side of the diagram.
Stand-by current drawing is negligible, so SW1 can be omitted.

Plant Watering Watcher Circuit Schematic

2010-01-04T13:13:00.005+05:00

A flashing LED signals the necessity to water a plant, 3V powered circuit

This circuit is intended to signal when a plant needs water. A LED flashes at a low rate when the ground in the flower-pot is too dry, turning off when the moisture level is increasing. Adjusting R2 will allow the user to adapt the sensitivity of the circuit for different grounds, pots and probe types.

Improvements:

This little gadget encountered a long lasting success amongst electronics enthusiasts since its first appearance on this website in 1999. Nevertheless, in the correspondence exchanged during all these years with many amateurs, some suggestions and also criticism prompted me to revise thoroughly the circuit, making some improvements requiring the addition of four resistors, two capacitors and one transistor.

This resulted in a more stable and easy to setup device, featuring a more visible flashing indicator with no resort to ultra bright LED devices. Extensive tests were also carried out with different flower-pots and probes. Although, as can be easily imagined, differences from various pots and probe types proved to be exceedingly high, typical resistance values across two 60mm long probes driven fully into the pot's ground about 50mm apart measured around 500 to 1000 Ohm with a high water content and about 3000 - 5000 Ohm when the ground was dry.

Circuit operation:

IC1A and related components R1 and C1 form a 2KHz square wave oscillator feeding one gate input of IC1B through the voltage divider R2/R3 made variable by adjusting the Trimmer R2. If the resistance across the probes is low (as when there is a sufficient quantity of water into the pot) C2 diverts the square wave to ground, IC1B is blocked and its output will go steady hight. IC1C inverts the high status to low, thus keeping IC1D blocked: the LED is off. When the ground in the flower-pot is becoming too dry the resistance across the probes will increase and C2 will be no longer able to divert the square wave to ground.

Therefore, IC1B output begins to transfer the 2kHz signal to IC1C which, in turn, passes it to the oscillator built around IC1D. No longer disabled by a low level on its input, the IC1D oscillator slowly pulses Q1 base low causing the LED to flash, signalling the necessity to water the plant.
The short low pulse driving the base of Q1 is actually a burst of 2kHz pulses and therefore the LED flickers about 2,000 times per second - appearing to the human eye as if the LED was steadily on for the entire duration of the pulse.

Circuit diagram:

Plant Watering Watcher Circuit Diagram

Parts:

R1 = 470K
R2 = 47K
R3 = 100K
R4 = 470K
R5 = 3.3K
R6 = 15K
R7 = 100R
C1 = 1nF-63V
C2 = 330nF-63V
C3 = 10µF-25V
C4 = 10µF-25V
D1 = 1N4148
D2 = 5mm. Red LED
Q1 = BC557 PNP Transistor
P1 = Probe (See Notes)
P2 = Probe (See Notes)
B1 = 3V Battery (2xAA, N or AAA 1.5V Cells in series)
IC1 = 4093 = Quad 2 input Schmitt NAND Gate IC

Notes:

A square wave is used to avoid problems of probes oxidization.
Probes are made with two pieces of bare, stiff lighting cable of 1mm diameter and should be about 60mm long.
The probes should be driven fully in the pot's ground about 30 - 50mm apart. Please note that all parameters regarding probes material, dimensions and spacing are not critical.
Current consumption: LED off = 150µA; LED on = 3mA for 0.1 sec. every about 2 sec. allowing the battery to last for years.
The quiescent current consumption is so low that the use of a power on/off switch was considered unnecessary. In any case, to switch the circuit completely off, you can short the probes.

..:: UPDATE ::..

Making Notes:

I’ve got it! I made it! So, I will leave a making note.
The total cost is USD ($6.00-, included tax). It is easy to make. If you make this, you should use super bright green LED. If not that, you could not know the time when is watering on time. Because is just the led was dimmed light. So, I have replaced 5mm red led by 5mm super bright green led. (You should consider that you have to place into the case, too).

In additionally, I use 3 volt lithium battery (CR2032) and its holder. It is cheap and small size. I had made this 2 weeks ago. There was no problem until now. I have been watering 5 days or so. R2(VR) setting tip: If you done to make, purring the water on the plant and then turn the R2 in order to led is off. It is easy and the end of making. That is all. P.S: I recommend the lead-free soldering for plant.

Thanks a lot Yongsik for submitting making notes.

Water Pump Relay Controller Circuit Schematic

2010-01-04T13:08:00.002+05:00

Water reservoir automatic level control, Simple circuitry - 12V supply

By means of a Relay, employed to drive a water pump, this circuit provides automatic level control of a water reservoir or well. The shorter steel rod is the "water high" sensor, whereas the longer is the "water low" sensor. When the water level is below both sensors, IC1C output (pin #10) is low; if the water becomes in contact with the longer sensor the output remains low until the shorter sensor is reached. At this point IC1C output goes high, Q1 conducts, the Relay is energized and the pump starts operating.

Now, the water level begins to decrease and the shorter sensor will be no longer in contact with the water, but IC1C output will be hold high by the signal return to pin #5 of IC1B, so the pump will continue its operation. But when the water level falls below the longer sensor, IC1C output goes low and the pump will stop. SW1 is optional and was added to provide reverse operation. Switching SW1 in order to connect R3 to pin #11 of IC1D, the pump will operate when the reservoir is nearly empty and will stop when the reservoir is full. In this case, the pump will be used to fill the reservoir and not to empty it as in the default operating mode.

Circuit diagram:

Water Pump Relay Control Circuit Diagram

Parts:

R1 = 15K - 1/4W Resistors
R2 = 15K - 1/4W Resistors
R3 = 10K - 1/4W Resistor
R4 = 1K - 1/4W Resistor
D1 = LED - any type and color
D2 = 1N4148 - 75V 150mA Diode
Q1 = BC337 - 45V 800mA NPN Transistor
IC1 = 4001 Quad 2 Input NOR Gate CMos IC
SW = SPDT Toggle or Slide Switch (Optional)
RL1 = Relay with SPDT 2A @ 230V switch
Coil Voltage 12V - Coil resistance 200-300 Ohm
Two steel rods of appropriate length

Notes:

The two steel rods must be supported by a small insulated (wooden or plastic) board.
The circuit can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the circuit's negative ground.

Midnight Security Light Circuit Schematic

2010-01-04T13:03:00.002+05:00

Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep. Here is an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am. It automatically resets in the morning. The circuit is fully automatic and uses a CMOS IC CD 4060 to get the desired time delay. Light-dependent resistor LDR1 controls reset pin 12 of IC1 for its automatic action. During day time, the low resistance of LDR1 makes pin 12 of IC1 ‘high,’ so it doesn’t oscillate.

After sunset, the high resistance of LDR1 makes pin 12 of IC1 ‘low’ and it starts oscillating, which is indicated by the fashing of LED2 connected to pin 7 of IC1. The values of oscillator components (resistors R1 and R2 and capacitor C4) are chosen such that output pin 3 of IC1 goes ‘high’ after seven hours, i.e., around 1 am. This high output drives triac 1 (BT136) through D5 and R3. Bulb L1 connected between the phase line and M2 terminal of triac 1 turns on when the gate of triac 1 gets the trigger voltage from pin 3 of IC1. It remains ‘on’ until pin 12 of IC1 becomes high again in the morning. Capacitors C1 and C3 act as power reserves, so IC1 keeps oscillating even if there is power interruption for a few seconds. Capacitor C2 keeps trigger pin 12 of IC1 high during day time, so slight changes in light intensity don’t affect the circuit.

Using preset P1 you can adjust the sensitivity of LDR1. Power supply to the circuit is derived from a step-down transformer T1 (230V AC primary to 0-9V, 300mA secondary), rectifed by a full-wave rectifer comprising diodes D1 through D4 and fltered by capacitor C1. Assemble the circuit on a general-purpose PCB with adequate spacing between the components. Sleeve the exposed leads of the components. Using switch S1 you can turn on the lamp manually. Enclose the unit in a plastic case and mount at a location that allows adequate daylight.

Circuit diagram:

Midnight Security Light Circuit Diagram

Parts:

P1 = 100K
R1 = 120K
R2 = 1M
R3 = 100R
R4 = 100R

C1 = 1000uF-25V
C2 = 100uF-25v
C3 = 100nF-63V
C4 = 1uF-25V

D1 = 1N4001
D2 = 1N4001
D3 = 1N4001
D4 = 1N4001
D5 = Red LED
D6 = Green LED
IC = CD4060
TR = BT136
T1 = 9v 300mA Transformer
L1 = 230V-60W Bulb
SW = On/Off Switch

Caution:

Since the circuit uses 230V AC, many of its points are at AC mains voltage. It could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to construct this circuit. We will not be responsible for any kind of resulting loss or damage.

Inverter Circuit For Soldering Iron

2010-01-04T13:00:00.003+05:00

Here is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 and Q2 (each BC547) form an astable multivibrator that produces 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to pnp Darlington driver stages formed by transistor pairs Q3-Q5 and Q4-Q6 (utilising BC558 and BD140).

The outputs from the drivers are fed to transistors Q7 and Q8 (each 2N3055) connected for push-pull operation. Use suitable heat-sinks for transistors Q5 through Q8. A 230V AC primary to 12V-0-12V, 4.5A secondary transformer (T1) is used. The centre-tapped terminal of the secondary of the transformer is connected to the battery (12V, 7Ah), while the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8, respectively.

When you power the circuit using switch S1, transformer X1 produces 230V AC at its primary terminal. This voltage can be used to heat your soldering iron. Assemble the circuit on a generalpurpose PCB and house in a suitable cabinet. Connect the battery and transformer with suitable current-carrying wires. On the front panel of the box, fit power switch S1 and a 3-pin socket for connecting the soldering iron. Note that the ratings of the battery, transistors T7 and T8, and transformer may vary as these all depend on the load (soldering iron).

Circuit diagram:

Inverter Circuit Diagram For Soldering Iron

Parts:

P1-P2 = 47K
R1-R2 = 1K
R3-R4 = 270R
R5-R6 = 100R/1W
R7-R8 = 22R/5W
C1-C2 = 0.47uF
Q1-Q2 = BC547
Q3-Q4 = BC558
Q5-Q6 = BD140
Q7-Q8 = 2N3055
SW1 = On-Off Switch
T1 = 230V AC Primary 12-0-12V
4.5A Secondary Transformer
B1 = 12V 7Ah