E Circuits Today

Simple Stereo Power Amplifier With 7905

noreply@blogger.com (Anonymous) — Thu, 21 Jun 2012 07:07:00 -0700

79xx is a widely known series of low-cost, fixed-negative-voltage regulators. These integrated circuits are available with output current of 100-150 mA (L series), 0.4-0.5A (M series), up to 1A (standard series), etc. They can be used in many applications other than regulators, audio power amplifier being one of them.

As shown in the circuit diagram, a simple stereo audio amplifier is built around two 7905 negative-voltage regulators (IC1 and IC2) and a few discrete components. The 7905 IC (a -5V regulator) used here is readily available. However, the circuit will also work with other 79XX regulators if appropriate power supply is used. Both channels shown in the diagram are identical. Hence the description below is only for the first channel. The quality of the output signal is within acceptable limits.

Circuit Diagram

Regulator IC 7905 works as an amplifier for the voltages applied to common pin2 (Ground or GND). The minimal voltage drop over the standard 7905 is around 2V and it depends on the output current. Feedback resistors in the IC set the gain of the channel internally. The amplifier is a class-A audio amplifier. The regulator IC produces the negative output signal.

Resistor R3 provides the positive signal. It limits the maximum output current of the regulator during the negative half period of the amplified sinusoidal signal. The minimal applicable value of R3 for the regulator 7905 is 8.2 to 10 ohms per 5W.

Optimisation of the value of R3 depends on the output voltage of the regulator, negative power supply (–5V) and load resistance of loudspeaker (LS1). If the required output current for LS1 is below 100 mA, the value of resistor R3 can be 33 to 51 ohms per watt.

Normally, the load resistance of the loudspeaker should be higher than of R3 in order to obtain a large peak-to-peak amplitude. But this can be neglected in order to obtain lower power dissipation on R3 and the IC.

The circuit works with any load resistance (R3 in parallel with LS1 as the load) under the condition that the regulator is not overloaded with current and power dissipation. However, it is preferable to use a loudspeaker with a high resistance (8 ohms, 16 ohms or more). The amplifier works well with low-impedance headphones having a resistance of 24 to 32 ohms. The voltage difference between the ground pin of 7905 and the output pin is fixed internally.

The input resistance of the amplifier is relatively low and depends on potentiometer VR1 and input resistance of the ground pin. Practically, any stereo output capable of driving 24- or 32-ohm headphones and loudspeakers can drive the input of the stereo amplifier with 7905. If VR1 is removed, the amplifier will still work but there will be more distortion. Therefore potentiometer VR1 is used to provide sufficient variable audio signal.

The values of output capacitors C10 and C11 are usually between 0.1 µF and 1 µF. A small resistance can be connected in series with them if needed.

S2 is the on/off switch. Switch S1 is for mono/stereo selection. When switch S1 is closed, the amplifier works as a two-way mono amplifier. If S1 is open, the amplifier works as a stereo amplifier.

The circuit is powered by a 12V battery. The positive terminal of the battery is the common node. The negative terminal is connected to pin 2 of IC1, which is the –12V supply line. The maximum operating voltage can be up to –35V.

If no input signal is applied, the DC voltage on the output of the regulator 7905 should be around –5V, which depends to some extent on the value of VR1. The maximum output current of 7905 can be up to 1A and the maximum power dissipation is up to 15W. IC 7905 has internal thermal protection.

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Fix the stereo female jack on the front panel and speaker to the rear side of the cabinet, and the 12V battery inside the cabinet. Fix LED1 and switches S1 and S2 too on the front panel of the cabinet. Mount the regulator IC 7905 on a heat-sink with thermal resistance below 15°C/W. The metallic part on the case is internally connected with the input pin of the regulator.

Digital Stopwatch 0-60sec Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:28:00 -0700

Introduction
By using the same circuit of the "Digital Stopwatch 0-99sec", we can add an AND gate, and transform the 0 � 99sec stopwatch to a 0 � 60sec stopwatch.
We must find a way to control the RESET function of the BCD counter, which is responsible for the counting of the seconds. As we studied above, the circuit resets when we have 99 to 100, that is 1001 1001 � 0001 0000 0000. To make a transformation successfully we must force the pulse from 59 to 60 0011 1001 � 0100 0000 on the output of the BCD counter.
By placing the AND gate, with its inputs on the Q1 and Q2 of the BCD counter of the decades, we make sure that when the gate closes, the RST input of the BCD counter will be set to logical '1', which on its turn, will force the circuit to start over. The transformed circuit appears in picture 2.

Circuit diagram

author:Koukos Konstantinos, Tsormpatzidis Dimitrios - Aristotle University of Thessaloniki,

Headlights Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:26:00 -0700

Pushbutton activated
Very simple circuitry

Circuit diagram

Parts:
R1 4K7 1/4W Resistor
R2,R3 1K 1/4W Resistors
C1 100�F 25V Electrolytic Capacitor (See Notes)
D1 1N4002 100V 1A Diode
Q1 BC547 45V 100mA NPN Transistor
Q2 BC327 45V 800mA PNP Transistor
P1 SPST Pushbutton
RL1 Relay with SPDT 10A min. switch
Coil Voltage 12V. Coil resistance 150-600 Ohms

Comments:
This device is a simple timer, allowing to keep on the headlights of your vehicle for about 1min. and 30sec., e.g. when accessing some dark place, without the necessity of coming back to switch-off the lights.

Circuit operation:
Pushing on P1 allows C1 charging to full 12V battery supply. Therefore Q1 is driven hard-on, driving in turn Q2 and its Relay load. The headlights are thus activated by means of the Relay contact wired in parallel to the vehicle's headlights switch. RL1 remains activated until C1 is almost fully discharged, i.e. when its voltage falls below about 0.7V.
The timing delay of the circuit depends by C1 and R1 values and was set to about 1min. and 30sec.
In practice, due to electrolytic capacitors wide tolerance value, this delay will vary from about 1min. and 30sec. to 1min. and 50sec.
An interesting variation is to use the inside lamp as a command source for the timer. In this way, when the door is opened C1 is charged, but it will start to discharge only when the door will be closed, substituting pushbutton operation.
To enable the circuit acting in this way, simply connect the cathode of a 1N4002 diode to R1-C1 junction and the anode to the "live" lead of the inside lamp.
This lead can be singled-out using a voltmeter, as it is the lead where a 12V voltage can be measured in respect to the vehicle frame when the lamp is on.

Notes:
The Relay contact must be rated at 10A or more.
Timings obtained trying different tolerance electrolytic capacitors for C1:
100�F = 1'30" to 1'50"
47�F = 0'45" to 1'05"
220�F = 3'15" to 4'15"

author:RED Free Circuit Designs,
website: http://space.tin.it/scienza/fladelle/

24 Second Shot Clock Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:25:00 -0700

Description:
This is a circuit intended to be used in basketball shot clock.

Circuit diagram

Notes:
To start in 24 seconds; 24s LOAD SW and Reset SW should be push simultaneously. If not, the count will start in 99. Pulse input can be connected to 555 astable multivibrator but must be calibrated for real time clock. The PAUSE SW must have a Switch Debouncer so that the counter will count normal when counting is paused and then turn-on.
When the count reach 00, the NOR gate will have an output of logic1 that will turn on the two transistor. The buzzer will rung and light will turn on. The two transistors are continuously turn-on not until LOAD SW and Reset SW is push. All have a +5v power supply.

author:Milardo de Guzman, milardo_dg@yahoo.com
website: http://www.zen22142.zen.co.uk

Jogging Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:24:00 -0700

3V Battery powered
Beeps after a fixed number of minutes

Circuit diagram

Parts:
R1 47K 1/4W Resistor
R2 10M 1/4W Resistor
R3 1M 1/4W Resistor
R4 12K 1/4W Resistor (see notes)
C1,C3 10�F 25V Electrolytic Capacitors
C2 100nF 63V Polyester Capacitor
D1 1N4148 75V 150mA Diode
IC1 4093 Quad 2 input Schmitt NAND Gate IC
IC2 4060 14 stage ripple counter and oscillator IC
IC3 4017 Decade counter with 10 decoded outputs IC
Q1 BC337 45V 800mA NPN Transistor
SW1 1 pole 9 ways Rotary Switch (see notes)
SW2 SPST Slider Switch
BZ1 Piezo sounder (incorporating 3KHz oscillator)
B1 3V Battery (two 1.5V AA or AAA cells in series etc.)

Device purpose:
This circuit was developed since a number of visitors of this website requested a timer capable of emitting a beep after one, two, three minutes and so on, for jogging purposes.
As shown in the Circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thing happens after 2 minutes, and so on, reaching a maximum interval of 9 minutes in position 9.

Notes:
Needing only one time set, rotary switch can be replaced by an hard-wired link.
A DIP-Switch can be used in place of the rotary type. Pay attention to use only a switch at a time, or the device could be damaged.
Varying R4 from 10K to 15K you can obtain more or less than three short beeps after the preset time delay.
To obtain a one-second beep only, after the preset time delay, disconnect pin 9 of IC1C from pin 9 of IC2 and connect it to pin 8 of IC1C.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/

Tan Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:23:00 -0700

Six timing positions suited to different skin types
Timing affected by sunlight intensity

Circuit diagram

Parts:
R1 47K 1/4W Resistor
R2 1M 1/4W Resistor
R3,R5 120K 1/4W Resistors
R4 Photo resistor (any type)
C1,C3 10�F 25V Electrolytic Capacitors
C2 220nF 63V Polyester Capacitor
D1,D2 1N4148 75V 150mA Diodes
IC1 4060 14 stage ripple counter and oscillator IC
IC2 4017 Decade counter with 10 decoded outputs IC
Q1 BC337 45V 800mA NPN Transistor
SW1 2 poles 6 ways Rotary Switch (see notes)
SW2 SPST Slider Switch
BZ1 Piezo sounder (incorporating 3KHz oscillator)
B1 3V Battery (two 1.5V AA or AAA cells in series etc.)

Device purpose:
This timer was deliberately designed for people wanting to get tanned but at the same time wishing to avoid an excessive exposure to sunlight.
A Rotary Switch sets the timer according to six classified Photo-types (see table).
A Photo resistor extends the preset time value according to sunlight brightness (see table).
When preset time ends, the beeper emits an intermittent signal and, to stop it, a complete switch-off of the circuit via SW2 is necessary.

Photo-type, Features and Exposure time
I & children Light-eyed, red-haired, light complexion, freckly 20 to 33 minutes
II Light-eyed, fair-haired, light complexion 28 to 47 minutes
III Light or brown-eyed, fair or brown-haired, light or slightly dark complexion 40 to 67 minutes
IV Dark-eyed, brown-haired, dark complexion 52 to 87 minutes
V Dark-eyed, dark-haired, olive complexion 88 to 147 minutes
VI The darkest of all 136 to 227 minutes
[color=green]Note that pregnant women belong to Photo-type I[/color]

Notes:
Needing only one time set suitable for your own skin type, the rotary switch can be replaced by hard-wired links.
A DIP-Switch can be used in place of the rotary type. Pay attention to use only a switch at a time when the device is off, or the ICs could be damaged.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/

Repeating Interval Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:22:00 -0700

Description:
This circuit has an adjustable output timer that will re-trigger at regular intervals. The output period can be anything from a fraction of a second to half-an-hour or more - and it can be made to recur at regular intervals of anything from seconds to days and beyond.

Circuit diagram

The Output Section:

The output section is a simple Monostable Circuit. When Pin 6 of the Cmos 4001 is taken high - the monostable triggers - and the relay energizes. It will remain energized for a period of time set by C1 & R3.
With the values shown - R3 will provide output periods of up to about 30-minutes. However, you can choose component values to suit your requirements. For example, if you reduce R3 to 1meg - and C1 to 4.7uF - the maximum output period is between 3 and 5 seconds. Owing to manufacturing tolerances - the precise length of the time period available depend on the characteristics of the actual components you've used.

The Cmos 4060:
The Cmos 4060 is a 14-bit binary counter with a built-in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11 - and its frequency is controlled by R7. The output from the oscillator is connected internally to the binary counter. While the oscillator is running - the IC counts the number of oscillations - and the state of the count is reflected in the output pins.
By adjusting R7 - you can set the length of time it takes for any given output pin to go high. Connect that output to Pin 6 of the Cmos 4001 and - every time it goes high - it'll trigger the monostable.
Ideally C4 should be non-polarized - but a regular electrolytic will work - provided it doesn't leak too badly in the reverse direction. Alternatively - you can simulate a non-polarized 10uF capacitor by connecting two 22uF capacitors back to back - as shown.

Veroboard Layout:

Since the delays between outputs can last for hours - or even days - using "Trial and Error" to set-up the timer would be very tedious. A better solution is to use the Setup Table provided - and calculate the time required for Pin 7 of the Cmos 4060 to go high.
For example, if you want the monostable to trigger every Six Hours - the Range Table tells you to use Pin 1 of the Cmos 4060. You need Pin 1 to go high every 6 x 60 x 60 = 21 600 seconds. The Setup table tells you that for Pin 1 you should divide this figure by 512 - giving about 42 seconds. Adjust R7 so that the Yellow LED lights 42 seconds after power is applied. This will cause Pin 1 to go high after about 3 Hours.

Setup Tables:

When Pin 1 goes high it will stay high for three hours. It will then go low for three hours - before going high once again. Thus, Pin 1 goes high once every six hours. It's the act of going high that triggers the monostable. So - after an initial delay of three hours - the relay will energize. It will then re-energize every six hours thereafter.
The reset button should NOT be used during setup. The time it takes for Pin 7 to go high - and the Yellow LED to light - MUST be measured from the moment power is applied.
Although R4, R5 and the two LEDs help with the setup - they are not necessary to the operation of the timer. If you want to reduce the power consumption - disconnect them once you've completed the setup.
The timer is designed for a 12-volt supply. However - provided a suitable relay is used - it will work at anything from 5 to 15-volts. Applying power starts the timer. It can be reset at any time by a brief interruption of the power supply - so a reset button is not strictly necessary. If you need delays in excess of 32-hours - increase the value of C4.
The Support Material for this circuit includes a step-by-step guide to the construction of the circuit-board - a parts list - a detailed circuit description - and more.

author:Ron J,
website: http://www.zen22142.zen.co.uk

Time Delay Relay II Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:20:00 -0700

When activated by pressing a button, this time delay relay will activate a load after a specified amount of time. This time is adjustable to whatever you want simply by changing the value of a resistor and/or capacitor. The current capacity of the circuit is only limited by what kind of relay you decide to use.

Circuit diagram

Parts:
C1 See Notes
R1 See Notes
D1 1N914 Diode
U1 4011 CMOS NAND Gate IC
K1 6V Relay
S1 Normally Open Push Button Switch
MISC Board, Wire, Socket For U1

Notes:
1. Email jawaharlal@excite.com with comments, questions, etc.
2. To calculate the time delay, use the equation R1 * C1 * 0.85=T, where R1 is the value of R1 in Ohms, C1 is the value of C1 in uF, and T is the time delay in seconds.
3. S1 may be replaced with an NPN transistor so the circuit can be triggered by a computer, other circuits, etc.
4. Most any 6V relay will work for K1. If you use a large relay, you my need to add a transistor to the output of the circuit in order to drive the larger load.

Author: jawaharlal@excite.com
website: http://www.aaroncake.net

Timed Beeper Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:18:00 -0700

Beeps 7.5 seconds after a preset time
Adjustable time settings: 15 sec. 30 sec. 1 min. 2 min. & others

Circuit diagram

Parts:
R1 220R 1/4W Resistor
R2 10M 1/4W Resistor
R3 1M 1/4W Resistor
R4 10K 1/4W Resistor
R5 47K 1/4W Resistor
C1 100nF 63V Polyester Capacitor
C2 22�F 25V Electrolytic Capacitor
D1 1N4148 75V 150mA Diode
D2 3mm. Red LED
IC1 4081 Quad 2 input AND Gate IC
IC2 4060 14 stage ripple counter and oscillator IC
Q1 BC337 45V 800mA NPN Transistor
P1 SPST Pushbutton (Start)
P2 SPST Pushbutton (Reset)
SW1 4 ways Switch (See notes)
PS Piezo sounder (incorporating 3KHz oscillator)
B1 3V Battery (2 AA 1.5V Cells in series)

Device purpose:
This circuit is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it's a modern substitute for the old sandglass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.

Circuit operation:
Pushing P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is approx. 4Hz. The LED D2, driven by IC1A & B, flashing at the same oscillator frequency, signals proper circuit operation. SW1 selects the appropriate pin of IC2 thus adjusting timing duration:
Position 1 = 15 seconds
Position 2 = 30 seconds
Position 3 = 1 minute
Position 4 = 2 minutes
When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After approx. 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push P2.

Notes:
SW1 can be any type of switch with the desired number of ways. If you want a single fixed timing duration, omit the switch and connect pins 9 & 13 of IC1 to the suitable pin of IC2.
The circuit's reset is not immediate. Pushing P2 forces IC2 to oscillate very fast, but it takes some seconds to terminate the counting, especially if higher timer's duration is chosen and the pushbutton is operated when the circuit has just started. In order to speed the reset, try lowering the value of R5, but pay attention: too low a value can stop oscillation.
Frequency operation varies with different brand names for IC2. E.g. Motorola's ICs run faster, therefore changing of C1 and/or R3 values may be necessary.
You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
An on-off switch is not provided because in the off state the circuit draws no significant current.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/

Periodic Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:16:00 -0700

Description:
A switched timer with equal make and equal space periods timing adjustable from over 6 minutes to 38 minutes.

Circuit diagram

Notes:
This timer circuit is similar to the 5 to 30 minute timer except that when switch S1 is closed, the on/off action of the circuit will continue indefinately until S1 is opened again. A 7555 time and low leakage type capacitor for C1 must be used. The 6 way rotary switch S3 adds extra resistance in series to the timing chain with each rotation, minimum resistance point "a" maximum point "f". The 7555 is wired as an equal mark/space ratio oscillator, the timing resistor chain R1 to R6, being connected back to the output of the timer at pin 3.The output pulse duration is defined as:-

T = 1.4 R1 C1

This gives on and off times of about 379 seconds for postion "a" of S3 (just over 6 minutes), to about 38 minutes at point "f". The times may of coourse be varied by altering R1 to R6 or C1.

author:Andy Collinson, anc@mitedu.freeserve.co.uk
website: http://www.zen22142.zen.co.uk

Asymmetric Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:15:00 -0700

Description:
A timer circuit with independent mark and space periods.

Circuit diagram

Notes:
A simple astable timer made with the 555, the mark (on) and space (off) values may be set independently. The timing chain consists of resistors Ra, Rb and capacitor Ct. The capacitor, Ct charges via Ra which is in series with the 1N4148 diode. The discharge path is via Rb into into pin 7 of the IC. Both halves of the timing period can now be set independently.

The charge time (output high) is calculated by:

T(on) = 0.7 Ra Ct

The discharge time (output low) is calculated by:

T(off) = 0.7 Rb Ct

Please note that the formula for T(on) ignores the series resistance and forward voltage of the 1N4148 and is therefore approximate, but T(off) is not affected by D1 and is therefore precise.

author:Andy Collinson, anc@mitedu.freeserve.co.uk
website: http://www.zen22142.zen.co.uk

5 to 30 Minute Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:13:00 -0700

Descriptipn:
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.

Circuit diagram

Notes:

Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type. Switch 3 adds an extra resistor in series to the timing chain with each rotation, the timing period us defined as :-

Timing = 1.1 C1 x R1

Note that R1 has a value of 8.2M with S3 at position "a" and 49.2M at position "f". This equates to just short of 300 seconds for each position of S3. C1 and R1 through R6 may be changed for different timing periods. The output current from Pin 3 of the timer, is amplified by Q1 and used to drive a relay.

Parts
Relay 9 volt coil with c/o contact (1)
S1 On/Off (1)
S2 Start (1)
S3 Range (1)
IC1 7555 (1)
B1 9V (1)
C1 33uF CAP (1)
Q1 BC109C NPN (1)
D1 1N4004 DIODE (1)
C2 100n CAP (1)
R6,R5,R4,R3,R2,R1 8.2M RESISTOR (6)
R8 100k RESISTOR (1)
R7 4.7k RESISTOR (1)

author:Andy Collinson, mailto:anc@mitedu.freeserve.co.uk
website: http://www.zen22142.zen.co.uk

24 Hour Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:10:00 -0700

Description:
These two circuits are multi-range timers offering periods of up to 24 hours and beyond. Both are essentially the same. The main difference is that when the time runs out, Version 1 energizes the relay and Version 2 de-energizes it. The first uses less power while the timer is running; and the second uses less power after the timer stops. Pick the one that best suits your application.

Notes:
The Cmos 4060 is a 14 bit binary counter with a built in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11; and its frequency is set by R3, R4 & C3.The green Led flashes while the oscillator is running: and the IC counts the number of oscillations. Although it's a 14 bit counter, not all of the bits are accessible. Those that can be reached are shown on the drawing.
By adjusting the frequency of the oscillator you can set the length of time it takes for any given output to go high. This output then switches the transistor; which in turn operates the relay. At the same time, D1 stops the count by disabling the oscillator. Ideally C3 should be non-polarized; but a regular electrolytic will work, provided it doesn't leak too badly in the reverse direction. Alternatively, you can simulate a non-polarized 10uF capacitor by connecting two 22uF capacitors back to back (as shown).
Using "Trial and Error" to set a long time period would be very tedious. A better solution is to use the Setup tables provided; and calculate the time required for Pin 7 to go high. The Setup tables on both schematics are interchangeable. They're just two different ways of expressing the same equation.
For example, if you want a period of 9 Hours, the Range table shows that you can use the output at Pin 2. You need Pin 2 to go high after 9 x 60 x 60 = 32 400 seconds. The Setup table tells you to divide this by 512; giving about 63 seconds. Adjust R4 so that the Yellow LED lights 63 seconds after power is applied. This will give an output at Pin 2 after about 9 Hours.
The Support Material for the timers includes a detailed circuit description - parts lists - a step-by-step guide to construction - and more. A suitable Veroboard layout for each version is shown below:

The timer was designed for a 12-volt supply. However, provided a suitable relay is used, the circuit will work at anything from 5 to 15-volts. Applying power starts the timer. It can be reset at any time by a brief interruption of the power supply. The reset button is optional; but it should NOT be used during setup. The time it takes for the Yellow LED to light MUST be measured from the moment power is applied. Although R1, R2 and the two LEDs help with the setup, they are not necessary to the operation of the timer. If you want to reduce the power consumption, disconnect them once you've completed the setup. If you need a longer period than 24-hours, increase the value of C3.

author:Ron J,
website: http://www.zen22142.zen.co.uk

Bedside Lamp Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:07:00 -0700

30 minutes operation
Blinking LED signals 6 last minutes before turn-off

Circuit diagram

Parts:
R1 1K 1/4W Resistor
R2 4K7 1/4W Resistor
R3 10M 1/4W Resistor
R4 1M 1/4W Resistor
R5 10K 1/4W Resistor
C1 470�F 25V Electrolytic Capacitor
C2-C4 100nF 63V Polyester Capacitors
D1-D4 1N4002 100V 1A Diodes
D5 5mm. Red LED
IC1 4012 Dual 4 input NAND gate IC
IC2 4060 14 stage ripple counter and oscillator IC
Q1 BC328 25V 800mA PNP Transistor
Q2 BC238 25V 100mA NPN Transistor
P1,P2 SPST Pushbuttons
T1 220V Primary, 9 + 9V Secondary 1VA Mains transformer
RL1 10.5V 470 Ohm Relay with SPDT 2A 220V switch
PL1 Male Mains plug
SK1 Female Mains socket

Device purpose:
The purpose of this circuit is that of power a lamp or other apparatus for a given time (30 minutes in this case), and then to turn it off. It's useful when reading at bed by night, turning off the bedside lamp automatically in case the reader falls asleep... After turn-on by P1 pushbutton, an LED lights for c25 minutes, but 6 minutes before the turn-off, start blinking for two minutes, then stop blinking for other two minutes and finally blinks for other two minutes, thus signaling that the on-time is ending. If the user want to prolong the reading, can earn another half-hour of light by pushing on P1. Turning-off the lamp at user's ease is obtained pushing on P2.

Circuit operation:
Q1 and Q2 forms an ALL-ON ALL-OFF circuit that in the off state draw no significant current. P1 starts the circuit, the relay is turned on and the two ICs are powered. The lamp is powered by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 start oscillating at a frequency settled by R4 and C4. With the values shown pin 3 goes high after c30 minutes, turning off the circuit via C3. During the c6 minutes preceding turn-off, the LED does a blinking action by connections of IC1 to pins 1,2 & 15 of IC2. Blinking frequency is provided by IC2 oscillator at pin 9. The two gates of IC1 are in parallel to source an higher current. If needed, a piezo sounder can be connected at pins 1 & 14 of IC1. Changing IC2 brand name, varies the oscillation frequency. In particular Motorola's ICs run faster. Obviously, time can be varied changing C4 and R4 values.

This circuit was awarded with publication in ELECTRONICS WORLD "Circuit Ideas", October 1999 issue, page 819.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/

Time Delay Relay Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:06:00 -0700

A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. The time is adjustable from 0 to about 20 seconds with the parts specified. The current capacity of the circuit is only limited by what kind of relay you decide to use.

Circuit diagram

Parts:
C1 10uf 16V Electrolytic Capacitor
C2 0.01uf Ceramic Disc Capacitor
R1 1 Meg Pot
R2 10 K 1/4 Watt Resistor
D1,D2 1N914 Diodes
U1 555 Timer IC
RELAY 9V Relay
S1 Normally Open Push Button Switch
MISC Board, Wire, Socket For U1

Notes:
1. R1 adjusts the on time.
2. You can use a different capacitor for C1 to change the maximum on time.
3. S1 is used to activate the timing cycle. S1 can be replaced by a NPN transistor so that the circuit may be triggered by a computer, other circuit, etc.

Author:
website: http://www.aaroncake.net

Photo Timer Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:05:00 -0700

Circuit diagram

Time is set by potentiometer R2 which provides a range or 1 sec. To 100 seconds with timing capacitor C1 of 100uF. The output at pin 3 is normally low and the relay is held off. A momentary push on switch S1 energies the relay which is held closed for a time 1.1 X (R1+R2). C1 and then released. The exact length of the timing interval will depend on the actual capacitance of C1. Most electrolytic capacitors are rated on the basis of minimum guaranteed value and the actual value may be higher. The circuit should be calibrated for various positions of the control knob of R2 after the timing capacitor has had a chance to age. Once the capacitor has reached its stable value, the timings provided should be well within the photographic requirements.

Parts
C1 - 100uF, 25V electrolytic
C2 - 0.01uF, disc ceramic
D1, D2 - DR50 or 1N4001
R!,R2 - 10K ohms, � watts
R3 - 1 M ohms, potentiometer
RLY1 - 12V, DC relay, operating current less than 200mA
S1 - Push-to-on switch
U1 - NE555 timer IC
P1 & P2 are for exposure lamp ckt.

Download this project in doc format

author:Ravi Sumithraarachchi, ravi@ualink.lk

Door Alarm Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:01:00 -0700

Hangs up on the door-handle
Beeps when someone touches the door-handle from outside

Circuit diagram

Parts:
R1 1M 1/4W Resistor
R2 3K3 1 or 2W Resistor (See Notes)
R3 10K 1/2W Trimmer Cermet (See Notes)
R4 33K 1/4W Resistor
R5 150K 1/4W Resistor
R6 2K2 1/4W Resistor
R7 22K 1/4W Resistor
R8 4K7 1/4W Resistor
C1,C2 10nF 63V Ceramic or Polyester Capacitors
C3 10pF 63V Ceramic Capacitor
C4,C6 100nF 63V Ceramic or Polyester Capacitors
C5 2�2 25V Electrolytic Capacitor
C7 100�F 25V Electrolytic Capacitor
D1,D2,D4 1N4148 75V 150mA Diodes
D3 5 or 3mm. Red LED
Q1,Q2,Q3,Q5 BC547 45V 100mA NPN Transistors
Q4 BC557 45V 100mA PNP Transistor
L1 (See Notes)
L2 10mH miniature Inductor
Hook (See Notes)
BZ1 Piezo sounder (incorporating 3KHz oscillator)
SW1,SW2 SPST miniature Slider Switches
B1 9V PP3 Battery
Clip for PP3 Battery

Device purpose:
This circuit emits a beep and/or illuminates a LED when someone touches the door-handle from outside. The alarm will sound until the circuit will be switched-off.
The entire circuit is enclosed in a small plastic or wooden box and should be hanged-up to the door-handle by means of a thick wire hook protruding from the top of the case.
A wide-range sensitivity control allows the use of the Door Alarm over a wide variety of door types, handles and locks. The device had proven reliable even when part of the lock comes in contact with the wall (bricks, stones, reinforced concrete), but doesn't work with all-metal doors.
The LED is very helpful at setup.

Circuit operation:
Q1 forms a free-running oscillator: its output bursts drive Q2 into saturation, so Q3 and the LED are off. When part of a human body comes in contact with a metal handle electrically connected to the wire hook, the body capacitance damps Q1 oscillations, Q2 biasing falls off and the transistor becomes non conducting. Therefore, current can flow into Q3 base and D3 illuminates. If SW1 is closed, a self-latching circuit formed by Q4 & Q5 is triggered and the beeper BZ1 is activated.
When the human body part leaves the handle, the LED switches-off but the beeper continues to sound, due to the self-latching behavior of Q4 & Q5. To stop the beeper action, the entire circuit must be switched-off opening SW2.
R3 is the sensitivity control, allowing to cope with a wide variety of door types, handles and locks.

Notes:
L1 is formed winding 20 to 30 turns of 0.4mm. diameter enameled copper wire on R2 body and soldering the coil ends to the resistor leads. You should fill R2 body completely with coil winding: the final turn's number can vary slightly, depending on different 1 or 2W resistor types actual length (mean dimensions for these components are 13-18mm. length and 5-6mm. diameter).
The hook is made from non-insulated wire 1 - 2mm. diameter (brass is well suited). Its length can vary from about 5 to 10cm. (not critical).
If the device is moved frequently to different doors, Trimmer R3 can be substituted by a common linear potentiometer fitted with outer knob for easy setup.
To setup the device hang-up the hook to the door-handle (with the door closed), open SW1 and switch-on the circuit. Adjust R3 until the LED illuminates, then turn slowly backwards the screwdriver (or the knob) until the LED is completely off. At this point, touching the door-handle with your hand the LED should illuminate, going off when the hand is withdrawn. Finally, close SW1 and the beeper will sound when the door-handle will be touched again, but won't stop until SW2 is opened.
In regular use, it is advisable to hang-up and power-on the device with SW1 open: when all is well settled, SW1 can be closed. This precautionary measure is necessary to avoid unwanted triggering of the beeper.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com

Everything-that-moves ALARM Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 23:00:00 -0700

A crucial failing of proximity detectors is their unreliable and tricky nature. This is where they are used to detect humans, not to speak of smaller living beings. One common approach is to detect eddy currents in a living body, which are induced in the body through a.c. mains wiring. However, such circuits become altogether unusable in the case of mains failure, or in the absence of mains electricity, or even where adjacent mains circuits are switched in and out.

Circuit diagram

The circuit of Fig.1 takes the guesswork out of proximity detection by inducing eddy currents in a living being, whether animal or human. Five turns of enamelled copper wire (say 30 s.w.g.) are wound around the area within which detection is to take place (4m x 4m in tests), and an audio signal of about � Watt is pulsed through this, the Tx, coil. A smaller Rx coil (say 100 turns of 30 s.w.g. enamelled copper wire wound on a 150mm dia. former) is used as a pick-up coil. The circuit is adjusted by means of tune and fine-tune controls VR1 and VR2, so that it is deactivated when one stands back from the Rx coil.

A simple clock generator (IC1a-IC1b) and power MOSFET (TR1) are used for the transmitter, and a 7555 timer (IC2) is wired as a sine-square convertor for the receiver. IC2's inputs are biased through VR1, VR2 and R4. IC2 in turn switches NAND gates IC1c and IC1d, to drive relay RLA. Capacitor C5 switches the relay for about two seconds, and its value may be increased or decreased to give different timing periods. D2 is critical to prevent back-e.m.f. from re-triggering the circuit. Supply decoupling capacitors C1 and C4 are also critical, and should be located close to IC1 and IC2 respectively.

When a living being - animal or human - comes within tens of centimetres of the Rx coil, the circuit is triggered. This coil may be placed in the threshold of a door, under a carpet, or around a hatch, at the base of a tree, and so on. A number of such coils may also be wired in series.

Coils may be wound with a larger or smaller diameter, with more or less turns, and the power of the transmitter may be varied, as well as the sensitivity of the receiver. Note that a.m. radio reception may be affected at close proximity to the Tx coil.

author:Thomas Scarborough,

Frost Alarm Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:58:00 -0700

Circuit diagram

Notes:
The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit.

5 Zone Alarm Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:57:00 -0700

Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppresser. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key. At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed.

LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Fridge door Alarm Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:56:00 -0700

Beeps if you leave open the door over 20 seconds
3V battery operation, simple circuitry

Circuit diagram:

Parts:
R1 10K 1/4W Resistor
R2 Photo resistor (any type)
R3,R4 100K 1/4W Resistors
C1 10nF 63V Polyester Capacitor
C2 100�F 25V Electrolytic Capacitor
D1,D2 1N4148 75V 150mA Diodes
IC1 4060 14 stage ripple counter and oscillator IC
Q1 BC337 45V 800mA NPN Transistor
BZ1 Piezo sounder (incorporating 3KHz oscillator)
SW1 Miniature SPST slide Switch
B1 3V Battery (2 AA 1.5V Cells in series)

Circuit operation:
This circuit, enclosed in a small box, is placed in the fridge near the lamp (if any) or the opening. With the door closed the interior of the fridge is in the dark, the photo resistor R2 has a high resistance (>200K) thus clamping IC1 by holding pin 12 high. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K), pin 12 goes low, IC1 starts counting and, after a preset delay (20 seconds in this case) the piezo sounder beeps for 20 sec. then stops for the same lapse of time and the cycle repeats until the fridge door closes. D2 connected to pin 6 of IC1 makes the piezo sounder beeping 3 times per second.

Notes:
Connecting D1 to pin 2 of IC1 halves the delay time.
Delay time can be varied changing C1 and/or R3 values.
Any photo resistor type should work well.
Current drawing is insignificant, so SW1 can be eliminated.
Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
Don't place it in the freezer.

author:RED Free Circuit Designs,
website: http://www.redcircuits.com/

Electronic Combination Lock Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:55:00 -0700

This circuit is very basic to build. To open a the lock which is connected to the K1 Load you must press each momentary switch in the correct sequence. The sequence used in this circuit is S1,S2,S3,S4. If any of the other switches are pressed the circuit will reset and you will need to start over. Depending on how you wire the switches, you can use any 4 switch combination.

Sun-Up Alarm

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:53:00 -0700

The Sun-Up Alarm can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. The circuit works as follows. The phototransistor is very sensitive to light. (Any phototransistor will work fine) The sun shining on this device will provide a high to one of the NAND gates. This will cause another NAND gate to oscillate which will drive another gate to output a 100hz tone. The transistor provides drive for the speaker.

Light Sensitive alarm

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:52:00 -0700

The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

- The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
- The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.

Remote Doorbell Warning Switch Circuit

noreply@blogger.com (Anonymous) — Wed, 20 Jun 2012 22:51:00 -0700

Circuit diagram

Important Note:
This circuit should only be used with the solenoid type chime doorbells, the electronic type that play tunes will not work here.

Notes:
The hardest part for this circuit was the title. It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication, i.e. a lamp. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from
the doorbell batteries or transformer. Using a series resistor R1 actually reduces current flow , and if run from batteries, will give them a longer life. The value of R1 is chosen so that about 0.6 to 0.7 volts is dropped across it, and the doorbell should
still ring. I used a combination of a 22 ohm resistor in parallel with a 50 ohm. The doorbell still rang and circuit operated correctly. I used to have an electromechanical counter that registered each time when someone pressed the switch....in fact, I remember a time when I had more "hits" at my doorbell then at my web site=