Top Circuits

CCFL Tester Circuit For LCD Screens

2014-03-25T22:50:00.000+05:30

Lcd's cover a wide range of applications including led tv's to cmputer monitors, PDAs, digital monitors and much more. LCD backlight mainly consists of a light source, diaphragm, light leading board and a plastic frame. Cold-cathode fluorescent lamps (CCFLs) have a phosphor coated glass cylinder with cathodes at each end. The CCFL inverter accepts a low-level DC input voltage and provides a high-level AC output to run the backlight CCFL tube. Here's a CCFL tester circuit that often needed to check a faulty LCD backlight circuit for finding the dead components.

Circuit schematic of CCFL tester.

The ciruit is portable6V battery operated and can be used to test almost all types of LCD backlight CCFL tubes.Here the NE555 timer IC is working as an astable multivibrator. This drives to drive a standard MOSFET T1 (IRF 512/IRF 830). Here an ordinary step-down transformer is used as the inverter transformer by reversing its primary and secondary windings.

Guitar Preamplifier Circuit Using IC TL071

2014-03-25T22:48:00.000+05:30

Here is the circuit of a electric guitar preamplifier based on IC TL071.The pickup device has a transducer on one end and a jack on the other end. The jack can be plugged into a preamplifier circuit and then to a power amplifier system.

The mechanical vibrations from low frequency bass to a certain extent of high frequency is picked up by a guitar or violin pickup device and converts them into an electrical signal, which can then be amplified by an audio amplifier. This circuit diagram of guitar pre amplifier has two output options - one to a power amplifier and other one could fed to a headphone.

Circuit Diagram of TL071 Guitar Preamplifier : Right Click >> View Image to view full size

Circuit Working

This preamp circuit is a a single-transistor common-emitter amplifier with degenerative feedback in the emitter and a boot-strapped bias divider to pick secure optimal input impedance. The maximum output voltage is 2V RMS.Master-level-control potmeter VR1 should be adjusted for minimal distortion.

Note:

Remember to enclose the circuit within a metallic case.
To prevent hum, ground the case and the pot enclosures.
Use a well regulated 9V Dc power supply.

150mW Crystal AM Transmitter

2014-03-14T20:13:00.000+05:30

Here is the circuit of a medium power crystal based amplitude modulation (AM) transmitter that can deliver 100-150mW of radio frequency (RF) power.

Circuit diagram of 150mW Crystal AM Transmitter : Click on image to enlarge

The heart of this circuit is a crystal oscillator. A 10MHz crystal is used to produce highly stable carrier frequency. The sound signal from the condenser mic is amplified by the amplifier circuit consist of transistors Q1, Q2 and Q3. The amplified audio signal modulates the RF carrier generated by the crystal oscillator built around transistor Q4. Here, modulation is done via the power supply source line. The amplitude modulated (AM) signal is obtained at the collector of oscillator transisitor Q4.

The use of matching dipole antenna and co-axial cable, the transmission range can be increased. The external wire antenna radio receiver can be used to obtain maximum range. The circuit works off a 9V-12V battery.

For oscillator coil L1: wind 14turns of 30SWG wire round an 8mm diameter radio oscillator coil former witha ferrite bead.

For Modulation transformer X1: You can use audio output transformer found in old transistor radios. Alternatively, you can make it from E/I core transformer lamination with inner winding having 40 turns of 26SWG wire and outer winding having 200 turns of 30SWG.

Assemble the circuit on a general purpose PCB and enclose within a suitable cabinent.

1Hz Clock Generator Circuit Using COB

2014-02-25T17:57:00.000+05:30

Let's familiarize with a COB - chip on board device by building a precision 1Hz clock generator. Circuits that usually generate 1Hz clock makes use of ICs with variable capacitors but they are not very precise. ( micro controller based one should be precise but it costs large ). better accuracy can be obtained by a COB found inside a digital clock, which is cheaply available in the market.

1Hz clock generator circuit diagram : Click on the image to enlarge

The COB is a small pcb consist of an IC chip capacitors and quartz crystal, etc. Here's the some important points to note before you assemble the clock generator.

R1, C3, diodes D1 and D2 shown in the circuit convert 5V DC into 1.4V DC which is the supply voltage to the COB.
A ½Hz clock is available at terminals A and B with a phase difference of 90o, these pins are coupled using capacitors C1 and C2 to obtain a complete 1Hz clock.
Op-amp IC CA3140 used to amplify the output of the COB to a considerable level.
R4 and R3 is used to set the gain of the op-amp.
T1 and T2 transistors further amplifies the clock output to drive the digital clocks and timers.
Preset VR1 is offset null control used to adjust proper 1Hz pulse at the output terminal ‘E’.
LED blinks every one second interval.

Simple Laptop Audio Amplifier Circuit

2014-02-23T16:38:00.001+05:30

When it comes to laptop sounding, most of the laptops currently in the market has very low sound output (laptops like DELL XPS is an exception). If you need more powerful sound, you need to amplify the sound output from the laptop. Here's a simple amplifier circuit making use of the SANYO LA4440 IC which is ideal for low power audio applications because it gives better sound clarity and less distortion.

Laptop audio amplifier circuit

Fortunately the circuit diagram is very simple and even a beginner can assemble and debug it. The circuit is built around the previously mentioned LA444o IC and a few components. The amplifier is a dual channel one with 6W for each channel. So a 10 W speaker would be very sufficient. Connect pins 2, 6 and ground of IC1 to the stereo jack which is to be used with the laptop.

LED Running Display Using NE555

2014-02-23T16:38:00.000+05:30

Here's a circuit to build a led based running display using easily available general purpose timer IC NE555 and a popular decade counter IC CD4017. This display consist of 24 LED's of four layers. The NE555 is wired as an astable multivibrator whose output triggers CD4017 counter.

Circuit diagram of LED based running effect display.

On powering up the circuit, timer starts oscillates to produce triggering pulses. This pulses trigger counter IC and it counts from 0 to 5. These outputs are fed to general purpose NPN transistors BC547 which are used as current drivers for each led layer. As each of the counter output goes hih, the curresponding led layer glows sequentially. After it counts upto 6 values, resets to zero and the process repeats.

How to display custom words using this circuit.

Suppose you want to display ‘STAR.’ Build letter S with L1,T with L2, A with L3 and R with L4.When the circuit is switched on, letter S glows first. Then S and T glow sequentially,followed by S, T and A, and thenS, T, A and R. When Q4 and Q5 outputs of the counter gohigh, the completeword ‘STAR’ glows.Thereafter, letter ‘S’glows again and the cycle repeats.

Simple Adjustable DC - DC Converter

2014-01-29T20:01:00.001+05:30

It's easier to generate DC from AC mains supply using a transforme and some diodes but the difficult part comes when we need to regulate the supply to feed sensitive devices such as mobile phones. Here's a versatile DC to DC coupler that 'll give you regulated fixed dc output voltages like 5V to charge mobile phone, 12V for external hard drives etc. You may use a 19V laptop adapter to route various voltages such as 5V , 6V, 12V from it.

Simple Adjustable DC - DC Converter circuit diagram

The circuit utilizes the well known adjustable dc voltage regulator IC LM317, BC 547 transistor and very few discrete components. By referring the circuit, variable voltages can be obtained by adjusting the preset VR1. The output voltage is read using a 0-100µA ammeter which has a series resistance necessary to cover the full working voltage range. For full-scale deflection (FSD) current of the meter is 100 µA and you need an output voltage of up to 15V, then R* = 15/0.0001 = 150 kΩ. The desired value of R* is obtained by using 150-kilo-ohm preset VR2. Other circuit details are self explanatory from the figure.

Automatic Muting Circuit For Audio Systems

2014-01-29T20:01:00.000+05:30

Here's a circuit diagram of automatic muting for audio systems using IC LB1403. The signal from pre-amplifier such as LA3160, LA3161 or HA1032 is connected to the base of the amplifier transistor BC548 (T1). Variable resistor VR1 is used to control the gain of input signal.

Working of the automatic muting Circuit

Comparator 2 output at pin 2 of LB1403 is used for generation of muting signal at the emitter (point A) of transistor T2, which can be directly connected to muting pin 4 of amplifier employing IC LA4440. As long as the audio input to the circuit of Fig. 1 is below a certain level (say, 150 mV peak to peak), the output at point A will be high. Once the input crosses this threshold level, the output will be around 0V. Capacitor C4 determines the ‘on’/‘off’ muting delay. Higher the value of this capacitor, greater will be the muting delay period.

Slight circuit modification will be needed if this circuit is used with STK series amplifiers, such as STK 4141, 4142, 4152, and 4191, because they need negative polarity voltage for muting. The additional circuit to be connected at point A in that case is shown in Fig. 2.

Digital Fan Regulator Circuit

2014-01-12T20:47:00.000+05:30

The circuit presented here is that of a digital fan regulator, variable to provide five speed levels as catered for in ordinary fan regulators. The circuit of ceiling fan controller makes use of easily available components. An optional 7-segment display with its associated electronic circuitry has been provided to display your choice of fan speed.

The heart of the circuit is a modulo-6 binary counter, built around IC2 and IC3 (IC 7476) which are dual JK flip-flops. The counter counts up in a straight binary progression from 000 to 101 (i.e. from 0 to 5) upon each successive clock edge and is reset to 000 upon next clock. The count sequence of the counter has been summarized in Table I. Each flip-flop is configured to toggle when the clock goes from high to low.

Circuit diagram of Digital Fan Regulator : Click on image to enlarge

Let us begin with the assumption that the counter reads 000 at power on. The monoshot built around IC1 (NE 555) provides necessary pulses to trigger the counter upon every depression of switch S1. Upon the arrival of first clock edge, the counter advances to 001. The outputs of the counter go to IC4 (IC 74138), which is a 3-line to 8-line decoder. When IC4 receives the input address 001, its output Q1 goes low, while other outputs Q0 and Q2 through Q7 stay high. The output Q1, after inversion, drives transistor T1, which actuates relay RL1. Now power is delivered to the fan through the N/O contact RL1/1 of relay RL1 and the tapped resistor RT. For the tapped resistor RT, one can use the resistance found in conventional fan regulators with rotary speed regulation.

The outputs of the counter also go to IC6 (IC 7447), a BCD to 7-segment code converter, which, in turn, drives a 7-segment LED display. When switch S1 is depressed once again, the counter advances to count 010. Now, the output Q2 of IC4 goes low, while Q0, Q1 and Q3 through Q7 go high or remain high. This forces transistor T2 to saturation and actuates relay RL2. The display indicates the counter output in a 7-segment fashion.

The counter proceeds through its normal count sequence upon every depression of switch S1 up to the count 101. When switch S1 is depressed once again, normally the counter should read 110. But the two most significant bits of the counter force the output of NAND gate (IC7) to go low to reset the counter to 000. The counter now begins to count through its normal sequence all over again, upon every key depression.

The circuit does not provide the facility to memorise its previous setting once it is powered off or when there is a mains failure.

Water Tank Level Meter

2014-01-12T20:46:00.001+05:30

The water-tank level meter described here is very simple circuit diagram and useful for monitoring the water level in an overhead tank (OHT). The water level at 30cm intervals is monitored and continuously indicated by LEDs arranged in a meter-format. When all the LEDs are ‘off’, it indicates that the OHT is empty. When the water level reaches the top limit, the whole LED-meter begins to flash. The height at which the level-sensing electrodes are fitted is adjustable. Thus, the minimum and maximum level settings may be varied as desired. The range of the meter can also be enlarged to cater to any level. No special or critical components are used. CMOS ICs are used tolimit the idle current to a minimum level.

Circuit diagram of Water Tank Level Meter : Click on image to enlarge

Even when all the LEDs are ‘on’, i.e. water reaches the top level, the demand on the power supply is reasonably low. Further, the extremely high input resistance of the Schmitt inverter gates reduces the input current and thus minimises the erosion of electrodes. The principal part of the device is its water-level sensor assembly. By using easily available material, it can be fabricated to meet one’s own specific requirements.
The common ground reference electrode ‘X’ is an aluminium conduit of 15mm outer diameter and 3-metre length, to cater to a 3-metre deep overhead tank. Insulating spacer rings ‘Y’ (10mm length, 15mm dia.) are fabricated from electrical wiring conduits of 15mm inner diameter. These are pushed tightly over the aluminum conduit at preferred places, say 30cm apart. If the pieces are too tight, they can be heated in boiling water for softening and then pushed over ‘X’.

The sensor electrodes ‘Z’ are made out of copper or brass strips (6mm wide and 1mm thick) which are shaped into rings that can tightly slip over the ‘Y’ pieces. The ends of these strips are folded firmly and formed into solder tags S1 to S10 and SG. The wall-mounting brackets, made of aluminium die-cast, are screwed directly on ‘X’ at two suitable places. The sensor cable ‘WC’ wires are soldered to solder tags, and some epoxy cement is applied around the joints and tags to avoid corrosion by water. The common ground reference wire ‘SG’ is taken from tag ‘T’. The cable’s individual wires from S1 to S10 and SG are cut and matched in length for a neat layout. The other ends of the cable are connected to the PCB terminal points S1 to S10 and SG respectively. No separate ground is needed.

The electronics portion is simple and straightforward. A long piece of veroboard can hold all the parts including the power supply section. For easy installation, the LEDs can be set at the track side of the board, in a single line, so that they may be pushed through the cutouts in the front panel of the enclosure from inside. The water level at 30cm intervals is monitored by corresponding sensors, causing the input to the concerned inverters (normally pulled ‘high’ via resistors R1 through R10) to go ‘low’, as soon as water reaches the respective sensors.

On initial switching ‘on’ of the power supply, when the tank is empty, all the electrodes are open. As a result, all the inverter inputs are ‘high’ (via the pull-up resistors R1 to R10) and their outputs are all ‘low’. Thus, all the LEDs are ‘off ’. As soon as the water starts filling the tank, the rising water level grounds the first sensor. The logic 1 output of first inverter gate N1 causes conduction of transistor T2 to extend ground to one side of resistors R14 through R23 via emitter-collector path of transistor T2. The LED D1 is thus lit up.

Similarly, other LEDs turn ‘on’ successively as the water level rises. As soon as the water in OHT reaches the top level, the output of gate N10 goes to logic 1 and causes flashing-type LED D11 to start flashing. At the same time, transistor T1 conducts and cuts off alternately, in synchronism with LED D11’s flash rate, to ground the base of transistor T2 during conduction of transistor T1. As a result, transistor T2 also starts cutting ‘off’ during conduction of transistor T1, to make the LED meter (comprising LEDs D1 through D10) flash and thus warn that the water has reached the top level. When the water level goes down, the reverse happens and each LED is turned ‘off’ successively.

The novel feature of this circuit is that whenever the water level is below the first sensor, all the LEDs are ‘off’ and the quiescent current is very low. Thus, a power ‘on’/‘off’ switch is not so essential. Even when the LED-meter is fully on, the current drawn from the power supply is not more than 120 mA. A heat-sink may, however, be used for transistor T2, if the tank is expected to remain full most of the time. A power supply unit providing unregulated 6V DC to 15V DC at 300mA current is adequate.

Caution: A point to be noted is that water tends to stick to the narrow space at the sensor-spacer junction and can cause a false reading on the LED-meter. This can be avoided if the spacers are made wider than 10 mm

Powerful Pest Repeller Circuit

2014-01-12T20:46:00.000+05:30

Most of the electronic pest repeller circuits have a major drawback of low power output hence their effectiveness suffers. The ultrasonic pest repeller circuit described here generates powerful ultrasonic signals therefore efficient to repel pests like mosquitoes. In addition to the ultrasonic frequency oscillator, we use a separate push-pull power amplifier and transformer to boost ultrasonic signals.

Circuit diagram of Powerful Pest Repeller: Click on image to enlarge

Ultrasonic frequency oscillator is built around IC CD4047. This IC provides complementary outputs. These complementary outputs are amplified by transistors T1 and T2 (BD139) to drive transistorised push-pull power amplifier stage comprising power transistors T3 and T4 (2N3055).

A tweeter is used to produce utrasonic frequency sound to repel pests. The power amplifier output is connected to the tweeter through transformer X1. Transformer X1 is wound over ferrite core (UU or CC core). Primary winding consists of 150 turns of 28 SWG while secondary winding comprises 40 turns of 24 SWG wire. Adjust potentiometer VR1 for maximum effectiveness.

Tips to Extend Life Of Solar SMF Battery

2014-01-05T21:04:00.000+05:30

Off-grid photo voltaic solar power equipment require a battery to store the energy accumulated during sunny hours for use at night. In most applications lead acid batteries are proffered as these are maintenance-free and do not emitany harmful gas while charging.

When fresh charging fails due to successive cloudy days, you may end up discharging your solar smf battery deeply and thus drastically reducing its life. This can be avoided if the battery has automatic protection agains deep discharge.

The life of a lead acid battery depends on, and is directly related to how deeply the battery is discharged. For instance, a 12V, 40ah battery can ideally store 12*40=480 Wh of energy, but to avoid damaging the battery or drastically reducing its life, you should not extract all its stored energy.

When the battery is discharged, its terminal voltage starts falling. You should stop discharging the battery when the terminal voltage reaches 10.5V minimum. The battery will certainly be damaged irreversibly if it is discharged any further.

Some batteries come with automatic protection against deep discharging. In these batteries discharging beyond a limit is prevented unless battery is recharged. This feature is especially useful for solar use at home since home users cannot detect whether they are discharging the SMF battery too deeply.

The charge-discharge cycle life of a sealed lead-acid battery is also directly related to its repetitive discharge rate. In solar applications, the battery is charged onceevery sunny day. So one day is one charge discharge cycle and the battery will provide good service for:

200 to 220 days (one year) with 100 percent depth of discharge (full discharge)
400 to 450 days (two years) with 50 percent depth of discharge (partial discharge)
1000 days (four years) with 30 percent depth of of discharge (shallow discharge)
1500 days (six years) with 15 percent depth of of discharge (rated discharge)

There are SMF batteries available for solar use which come with integral protection to assure four to five years of minimum battery life.

Bass And Treble Circuit Using Transistor

2014-01-05T21:03:00.002+05:30

This circuit diagram for bass and treble control is effective and using low cost components.

Modern audio frequency amplifiers provide flat frequency response over the whole audio range from 16 Hz to 20 kHz. To get faithful reproduction of sound we need depth of sound, which is provided by bass (low notes). Hence low-frequency notes should be amplified more than the high-frequency notes (treble). To cater to the individual taste, and also to offset the effect of noise present with the signal, provision of bass and treble controls is made. The combined control is referred to as tone control.

Circuit diagram of Bass And Treble Using Transistor: Click on image to enlarge

The circuit for bass and treble control shown in the figure is quite simple and cost-effective. This circuit is designed to be adopted for any stereo system. Here, the power supply is 12-volt DC, which may be tapped from the power supply of stereo system itself. For the sake of clarity, the figure here shows only one channel (the circuit for the other channel being identical). The input for the circuit is taken from the output of preamplifier stage for the left as well as right channel of the stereo system.

Potentiometer VR1 (10-kilo-ohm) in series with capacitor C4 forms the treble control. When the slider of potentiometer VR1 is at the lower end, minimum treble signal develops across the load. The lowest point is referred to as treble cut. As the slider is moved upward, more and more treble signal is picked up. The highest point is referred to as treble boost.

Bass would be cut if capacitive reactance in series with the signal increases. Thus, when the slider of potentiometer VR2 is at the upper end, capacitor C1 is shorted and the signal goes directly to the next stage, bypassing capacitor C1. Hence, bass has nil attenuation, and it is called bass boost. When the slider is at
the lowest end, capacitor C1 is effectively in parallel with potentiometer VR2. In this position, bass will have maximum attenuation, producing bass cut. Bass boost and bass cut are effective by ±15 dB at 16 Hz, compared to the output at 1 kHz. Treble boost and treble cut are also effective by the same amount at 20kHz, compared to the value at 10 kHz.

After assembling the circuit, we may check the performance of the bass and treble sections as follows:

1. Set the slider of the potentiometers at their mid-positions.
2. Turn-on the stereo system.
3. Set the volume control of stereo system at mid-level.

4. Set the slider at the position of optimum sound effect.

This circuit can be easily assembled using a general-purpose PCB.

Digital Water Level Indicator

2014-01-05T21:03:00.001+05:30

This digital water level meter circuit indicates up to 65 discrete water levels in the overhead tank (OHT). This
helps to know the quantity of water in the OHT quite precisely. The circuit is specially suited for use in apartments, hostels, hotels, etc, where many taps are connected to one OHT. In such cases, if someone for gets to close the tap, this circuit would alert the operator well in time.

IC's Used:

IC1 & IC2 : CD4033B
IC3 & IC4 : NE555

Normally, for multi water level readings, one has to use complicated circuits employing multi-core wires from the OHT to the circuit. This circuit does away with such an arrangement and uses just a 2-core cable to monitor various water levels. Fig. 2. shows various water levels and the corresponding readings on 7-sement displays.

Circuit diagram of Digital Water Level Meter: Click on image to enlarge

IC1 and IC2 shown in Fig.1 are CD4033 (decade up counter cum 7-segment decoder) which form a two-digit frequency counter. The CK pin 1 and CE pin 2 of IC1 are used in such a way that the counter advances when pin 1 is held high and pin 2 undergoes a high-to-low transition.

For water level reading, this frequency counter needs two types of inputs. One of the these is a continuous 30Hz clock (approx.), which is applied to pin 2 of IC1. The other is a timing pulse, which is applied to pin 1 of IC1. It comprises a positive pulse of variable duration (0.5 second to 3 seconds, depending upon the water level in the tank) followed by 4-second low level. Thus, during positive duration of timing pulse at pin 1 of IC1, the frequency counter is allowed to count the number of negative going pulses which are continuously available at its pin 2. At the same time the pnp transistor T1 remains cut-off ndue to the positive voltage at its base, and so the displays (DIS.1 and DIS.2) remain off. However, at the end of positive pulse at pin 1 of IC1 (and base of transistor T1), the frequency counter is latched. During the following 4-second low level period,
transistor T1 conducts and displays DIS.1 and DIS.2 show the current count. At beginning of the next positive timing pulse the frequency counter resets (as the reset pin 15 of IC1 and IC2 receives a differentiated positive going pulse via capacitor C1) and starts counting afresh.

Thus, this digital water level meter shows water level reading for four-second duration and then goes off for a variable period of 0.5 second to 3 seconds. Thereafter the cycle repeats. This type of display technique is very useful, because if there is ripple in water, we shall otherwise observe rapid fluctuations in level readings, and shall not get a correct idea of the actual water level.

Timer IC4 is used as a free-running astable multivibrator which generates continuous 30Hz clock pulses with 52 % duty cycle. The output of IC4 is available at its pin 3, which is connected to pin 2 of IC1.

The other timer, IC3, is used as timing pulse generator wherein we have independent control over high and low duration (duty cycle) of the timing pulses available at its output pin 3. The different duration of high and
low periods of the timing pulses are achieved because the charging and discharging paths for the timing capacitor C2 differ. The charging path of capacitor C2 consists of resistor R19, diode D1, and potmeters VR1 for OHT (or VR2 for sump tank, depending upon the position of slide switch S1) and VR3. However, the discharge path of capacitor C2 is via diode D2 and variable resistor VR4. By adjusting preset VR4, the low-duration pulse period (4 seconds) can be set. The low-pulse duration should invariably be greater than 3 seconds. Potmeter VR1 (or VR2) , a l inear wirewound pot, is fitted in such a way in the overhead tank (or sump tank) that when water level is minimum, the value of VR1 = 2 kilo-ohm. When water level in the tank is maximum, the in-circuit value of potmeter VR1 increases to 340-kilo-ohm (approximately). This is achieved by one third movement of pot shaft. The change in resistance of VR1 results in the change in charging period of capacitor C2. Thus, depending upon the level of water in the tank, the in-circuit value of VR1 (or VR2) resistance changes the charging time of capacitor C2 and so also the duration of positive pulse period of IC3 from 0.5 second to 3 seconds. Adjustment of presets for achieving the desired accuracy of count can be ac-
complished, without using any frequency counter, by using the following procedure (which was adopted by the author during calibration of his prototype):

First adjust the values: VR1 (or VR2) = 2 kilo-ohm, VR3 = 64 kilo-ohm, VR4 = 90 kilo-ohm, VR5 = 23.5 kilo-ohm.
Now switch on the circuit. The 7 segment DIS.1 and DIS.2 blink. If necessary, adjust VR3 such that the display goes ‘on’ for 4-second period.
If display readout is 15, increase value of pot VR1 from 2-kilo-ohm to 340 kilo-ohm. Now, the display should show 90. If there is a difference in the displayed count, slightly adjust presets VR5 and VR3 in such a way that when VR1 is 2-kilo-ohm the display readout is 15, and when VR1 is 340-kilo-ohm the display readout is 90.
If 15- to 90-count display is achieved with less than one-third movement of pot shaft, increase the value of VR5 slightly. If 15- to 90-count display is not achieved with one-third movement of pot shaft, decrease value of VR5.

If you need this digital water level meter to monitor the levels of water in the overhead as well as the sump tanks, it can be done by moving DPDT slide switch to down (DN) position. The indication of the position selected is provided by different colour LEDs (refer Figs 1 and 2) or by using a single bi-colour LED. To monitor water level in more than two tanks, one may use a similar arrangement in conjunction with a rotary switch. For timing capacitors C2 and C4 use tantalum capacitors for better stability.

Automatic Bathroom Light

2013-12-27T10:06:00.000+05:30

This is a circuit of automatic bathroom light which can be used to automate the working of a bathroom light. It is designed for a bathroom fitted with an automatic door-closer, where the manual verification of light status is difficult. The circuit also indicates whether the bathroom is occupied or not. The circuit uses only two ICs and can be operated from a 5V supply. As it does not use any mechanical contacts it gives a reliable performance.

One infrared LED (D1) and one infrared detector diode (D2) form the sensor part of the circuit. Both the infrared LED and the detector diode are fitted on the frame of the door with a small separation between them as shown in Fig. 1. The radiation from IR LED is blocked by a small opaque strip (fitted on the door) when the door is closed. Detector diode D2 has a resistance in the range of meg-ohms when it is not activated by IR rays. When the door is opened, the strip moves along with it. Radiation from the IR LED turns on the IR detector diode and the voltage across it drops to a low level.

Comparator LM358 IC2(a) compares the voltage across the photo detector against a reference potential set by preset VR1. The preset is so adjusted as to provide an optimum threshold voltage so that output of IC2(a) is high when the door is closed and low when the door is open. Capacitor C1 is connected at the output to filter out unwanted transitions in output voltage generated at the time of opening or closing of the door. Thus, at point A, a low-to-high going voltage transition is available for every closing of the door after opening it. (See waveform A in Fig.2.)

The second comparator IC2(b) does the reverse of IC2(a), as the input terminals are reversed. At point B, a low level is available when the door is closed and it switches to a high level when the door is opened. (See wave form B in Fig. 2.) Thus, a low to-high going voltage transition is available at point B for every opening of the door, from the closed position. Capacitor C2 is connected at the output to filter out unwanted transitions in the output voltage generated at the time of closing or opening of the door.

Circuit diagram of Automatic Bathroom Light : Click on image to enlarge

IC 7474, a rising-edge-sensitive dual-D flip-flop, is used in the circuit to memorise the occupancy status of the bathroom. IC1(a) memorises the state of the door and acts as an occupancy indicator while IC2(b) is used to control the relay to turn on and turn off the bathroom light. Q output pin 8 of IC1(b) is tied to D
input pin 2 of IC1(a) whereas Q output pin 5 of IC1(a) is tied to D input pin 12 of IC1(b).

At the time of switching on power for the first time, the resistor-capacitor combination R3-C3 clears the two flip-flops. As a result Q outputs of both IC1(a) and IC1(b) are low, and the low level at the output of IC1(b) activates a relay to turn on the bathroom light. This operation is independent of the door status (open/closed).

The occupancy indicator red LED (D3) is off at this point of time, indicating that the room is vacant. When a person enters the bathroom, the door is opened and closed, which provides clock signals for IC1(b) (first) and IC1(a). The low level at point C (pin 5) is clocked in by IC1(b), at the time of opening the door, keeping the light status unchanged. The high level point D (pin 8) is clocked in by IC1(a), turning on the occupancy indicator LED (D3) on at the time of closing of the door. (See waveform C in Fig. 2.) When the person exits the bathroom, the door is opened again. The output of IC1(b) switches to high level, turning off
the bathroom light. (See waveform D in Fig. 2.) The closing of the door by the door-closer produces a low-to-high transition at the clock input (pin 3) of IC1(a). This clocks in the low level at Q output of IC1(b) point D to Q output of IC1(a) point C, thereby turning off the occupancy indicator.

PC Based Wireless Stepper Motor control Circuit

2013-12-27T10:04:00.001+05:30

Stepper motors find lots of applications in process control, machine tools and robotics. Especially in robotics and process control, bit is necessary to control the stepper motor from a remote place. Here you will get the transmitter and receiver circuit diagrams and Full source code for the application program.

Here we describe how to wirelessly control a stepper motor from a remote place by using RF modules. For this wireless stepper-motor control system, you need to design and develop the required hardware and software. The parallel port of the PC is used to control the direction of the stepper motor at the transmitter side. RF interface is used instead of IR to overcome all the drawbacks of the IR interface. The PC signals are transmitted from the RF transmitter and received by the RF receiver.

Working Of the Wireless Stepper Motor controller

Block Diagram :

Figure 1.block diagram for PC-based wireless control of a stepper motor.

Fig. 1 shows the block diagram for PC-based wireless control of a stepper motor. The signals from the parallel port of the PC are interfaced to the RF transmitter through an encoder. The encoder continuously reads the status of the relay switches, passes the data to the RF transmitter and the transmiter transmits the data. At the receiving end, the RF receiver receives this data and gives it to the decoder. The decoder converts the single-bit data into four-bit data and presents to the stepper-motor driver. Now, the driver per-

forms the corresponding action, i.e., it rotates the stepper motor clockwise or anticlockwise.

Remote control: For remote control, we have used the Holtek encoder-decoder pair of HT12E and HT12D. Both of these are 18-pin DIP ICs.

Operation of Holtek HT12E and HT12D : HT12E and HT12D are CMOS ICs with a working voltage r a n g e o f 2.4V to 12V.

Encoder HT12E has eight address and another four address/data lines. The data set on these twelve lines (address and address/data lines) is serially transmitted when transmit-enable pin TE is taken low. The data output appears serially on DOUT pin. It is transmitted four times in succession. The data consists of differing
lengths of positive-going pulses for ‘1’ and ‘0,’ the pulse width for ‘0’ being twice the width of the pulse
for ‘1.’ The frequency of these pulses may lie between 1.5 and 7kHz depending on the resistance value between OSC1 and OSC2 pins. The internal oscillator frequency of decoder HT12D is 50 times the oscillator frequency of encoder HT12E. The values of timing resistors connected between OSC1 and OSC2 pins of HT12E and HT12D, for the given supply voltages, can be found out from the graphs given in the datasheets of the respective chips. The resistance values used in the circuits are chosen here for approximately 3kHz frequency of the encoder (HT12E) at Vcc of 9V and 150 kHz of the decoder (HT12D) at Vcc of 5V.

The HT12D receives the data from the HT12E on its DIN pin serially. If the address part of the data received
matches the levels on A0 through A7 pins four times in succession, the valid transmission pin (VT) is taken high. The data on pins AD8 through AD11 of the HT12E appear on pins D8 through D11 of the HT12D. Thus the device acts as a receiver of 4-bit data (16 possible codes) with 8-bit addressing (256 possible channels).

Once the frequency of the pair is aligned, then on ground of any data pin of the encoder, LED1 of the decoder should glow. You can also check the transfer of data on pins AD8 through AD11, which is latched to D8 through D11 pins of the decoder once TE pin is momentarily taken low by grounding it through diodes D1 through D4.

RF transmitter and receiver: RF transmitter and receiver modules from Alpus India, Mumbai, have been used for RF remote control. The RF transmitter TX-433 is AM/ASK type.

Fig 4: Circuit diagram of transmitter for wireless stepper motor control : Click on image to enlarge

Transmitter: Fig. 4 shows the circuit of the transmitter for wireless stepper motor control. The receiver address to be transmitted can be set with the help of 8-way DIP switch SW1. When any of the switch contacts is open the respective pin will be at logic 1, and when any of the switch contacts is closed the respective pin will be at logic 0. The data pins are pulled high via resistors R2 through R5. When pin 2 of the parallel port goes high, transistor T1 is driven into saturation and relay RL1 energises. Pin 10 (AD8) goes low through relay RL1 contacts and a ‘0’ is sent at that data position, while other data pins repre-sent logic-1 state. The logic circuitry at the receiver-decoder end decodes the data appropriately for controlling the
stepper motor.

Fig 7: Circuit diagram of receiver-cum-decoder for wireless stepper motor control. : Click on image to enlarge

Receiver and decoder : Fig. 7 shows the circuit of the receiver-cum-decoder for wireless stepper motor control. Assuming that identical address is selected on the encoder and decoder, when any of the data pins of the PC’s parallel port on the transmitter side is low, the corresponding data pin of the decoder will go low. The data outputs (D8 through D11) of HT12D are fed to inverters N1 through N4, which, in turn, are connected to driver ULN2003. The low output of ULN2003 drives the stepper motor. When any data is received, valid transmission (VT) pin goes high to drive transistor T5 into saturation and LED1 lights
up.

Software to control the stepper motor

The software program for the user interface to control the stepper motor is written in ‘C’ language. The signals are generated by the outport( ) function. The speed of rotation of the stepper motor can be varied by changing the argument of the delay( ) function. Direction of rotation (clockwise or anticlockwise) depends on the switch function.When the program (WSTEPPER.C) is loaded and run, the screen shows the welcome message. Pressing any key will lead to the main screen. The main screen displays three messages. Pressing ‘c’ key rotates the stepper motor in clockwise direction, while pressing ‘a’ key rotates the stepper motor in anti-clockwise direction. The program can be terminated by pressing ‘q’ key.

Click here to download the C program for controlling stepper motor.

PARTS LIST

Semiconductors:

IC1 - HT12E Holtek encoder
IC2 - 7806, 6V regulator
IC3 - HT12D Holtek decoder
IC4 - CD40106 hex inverter
IC5 - ULN2003 Darlington array
T1-T4 - BC547 npn transistor
T5 - BC548 npn transistor
D1-D4 - 1N4148 switching diode
D5-D10 - 1N4007 rectifier diode
TX1 - TX-433 RF transmitter
RX1 - RX-433 RF receiver
LED1 - 5mm LED

Resistors (all ¼-watt, ±5% carbon):

R1 - 1-mega-ohm
R2-R5 - 10-kilo-ohm
R6-R9 - 1.2-kilo-ohm
R10 - 1-kilo-ohm
R11 - 47-kilo-ohm
R12 - 3.9-kilo-ohm
R13 - 470-ohm

Capacitors:

C1, C3 - 100µF, 16V electrolytic
C2 - 0.1µF ceramic disk
C4 - 10µF, 16V electrolytic

Miscellaneous:

BATT.1 - 9V battery
BATT.2 - 6V, 4.5Ah battery
S1, S2 - On/off switch
DIP-SW1,
DIP-SW2 - 8-way DIP switch
- 25-pin D-type male
connector

Courtesy : Electronics For You : www.efymag.com

Seismic Sensor Circuit

2013-12-20T13:14:00.000+05:30

This circuit is a very sensitive seismic sensor that detects vibrations/sounds. It can detect seismic vibration or sounds caused by animals or humans. So it can be used to monitor protected areas to restrict entry of unwanted persons or animals.

Circuit Diagram Seismic Sensorof : Click to enlarge

This circuit is composed of readily available components and the design is very simple. A standard piezo sensor is used to detect vibrations/sounds due to pressure changes. The piezo element acts as a small capacitor having a capacitance of a few nanofarads. Like a capacitor, it can store charge when a potential is applied to its terminals. It discharges through VR1, when it is disturbed. In the circuit, IC TLO71 (IC1) is wired as a differential amplifier with both its inverting and non-inverting inputs tied to the negative rail through a resistive network comprising R1, R2 and R3.

At normal conditions, the difference in input voltages is zero so that the output is low. TLO71 is a low-noise JFET input op-amp with low input bias and offset current. TLO71 is a low-noise JFET input op-amp with low input bias and offset current. The BIFET technology provides fast slew rates. Capacitor C1 is provided in the circuit to keep the differential input of IC1 for better performance.

When the piezo element is disturbed (by even a slight movement), it discharges the stored charge. This alters the voltage level at the inputs of IC1 and the output momentarily swings high as indicated by green LED1. This high output is used to trigger switching transistor T1, which triggers monostable IC NE555. The timing period of IC2 is determined by R7 and C5. With the shown values, it will be around two minutes. The high output from IC2 activates T2 and the buzzer starts beeping along with red light indication from LED2.

Laser Switch With Timer

2013-12-16T23:32:00.000+05:30

This circuit is a laser controlled relay switch with timer that can be made using readily available components. This laser switch has the following advantages :

Timed operation - Turn on time of the switch can be controlled
Large current handling capability, can control a motor
Stand by and operating mode led indication
operating mode Piezo alert.

Circuit Diagram of Laser Switch With Timer: Click to enlarge

Here we can use a laser diode as a light transmitter or you can use any other laser pointer. In this laser switch the laser diode LED1 is protected by diode D1, and resistor R1 from over current flow.

Working Principle

When the laser beam produced by laser led falling on T1 photo-transistor, it conducts and reverse biases transistor T3 thereby making input of gate N1 of IC1. This makes stand by led driver T4 to conduct and the green led indicating stand by mode will glow continuously.

If anyone interrupts the flow of laser beam to T1, it stops conducting and T3 becomes forward bias and standby led will turn off (output of gate N1 will be low). Simultaneously, the low output of gate N1 makes the output of gate N2 high. This triggers triggers the monostable multivibrator employing gate N3 and N4 of the IC1. Resistor R8 and capacitor C1 determines the time period. This triggers the second monostable built around IC CD4538. As a result, relay RL1 get activated. This operating mode is indicated by LED3. Also piezo buzzer produces an alert that the relay is turned on.The transistor T5 is used to drive the relay and T6 is used to drive the intermittent piezobuzzer.

The turn on time of the laser switch can be controlled by the preset VR2. This controls the time period of second monostable.

Notes:

IC1 is a CD4001 (N1-N4) gates.
Circuit works off 12V dc supply
Regulator 7805 makes sure the proper working of CMOS IC's.

If you have any doubts, please mention it in the comments field.

Servo Motor Tester Circuit

2013-12-15T09:25:00.002+05:30

This circuit allows you to isolate the servo motor from the project circuit and feed it with pulses of varying width nd checking the angle that the servo motor turns to. the circuit is built using two NE555 IC's and a few discrete components. IC1 is set as an astable multivibrator with a time period of 20 ms. Every 20 ms, the astable provides a very sharp negative pulse to trigger IC2. Timer IC2 is configured as a monostable multivibrator that produces 1ms, 1.5ms and 2ms long pulses to rotate the servo motor (M1).

When pressing the switch S1, the astable multivibrator triggers the monostable to produce a pulse as per the position of switch S2. Switch S2 can select resistors R4, R5 and R6 together, and R7 to produce monostable pulse output of 1 ms, 1.5 ms and 2 ms, respectively. Preset VR1 is used to set the time period of IC1 to 20 ms.Using switch S2, select the monostable time period as 1 ms, 1.5 ms or 2 ms and press switch S1. The servo motor should rotate to extreme left, middle or extreme right, respectively.

Circuit diagram - servo motor tester.

Car Reverse Horn With Flasher

2013-12-15T09:25:00.000+05:30

This is a circuit of car reversing horn with normal auto lamp flasher that uses timer ICs NE556 and NE555. When the car is in reverse gear, the switch S1 which is the reverse gear switch of the car get shorted and the monostable timer give a high output. So the diode D1 and D2 goes for high for a time period R4C4.

Circuit Diagram of Car Reverse Horn With Flasher : Click to enlarge

Now the astable multivibrator starts oscillating which will drive the speaker through capacitor C6. When output of D1 and D2 goes low multivibrator is disabled to stop oscillating there by disabling sound through speaker.

The flasher circuit is very simple and composed of common 555 IC which drives a square wave. This drives the 12V, 10W auto bulb through transistor TIP31.

Note:

Assemble the circuit on a common PCB.

Connect point A & B to car reverse gear switch S1.

Portable Electric Lamp cum LED Flasher

2013-12-11T14:30:00.001+05:30

Here's the circuit of a portable type flasher uses 25W, 230V AC bulb and nine LEDs. The bulb and led's glows alternatively. The circuit includes a 555 timer based astable multivibrator which generates a square wave. This output drives the transistor bc547 to riger the gate of lamp controller triac.

Circuit Diagram of Portable Electric Lamp cum LED Flasher: Click to enlarge

The idea of flashing the led's and the lamp alternatively is very simple. When the transistor T1 conducts, the collector voltage drops so tuning off the leds. During this time triac BT136conducts and lamp glows. Similarly when T1 is off, led'd get forfard bias and lamp become off.

The flashing rate can be controlled by potentiometer VR1. Assemble the circuit on a common PCB and enclose within a suitable plastic cabinet. Also take care to avoid electic shock.

Simple Duophone System

2013-12-11T14:30:00.000+05:30

Here a simple circuit diagram of duophone that allows you to access two telephone line through a single telephone set. The conversation through each line will entirely private when the conference switch in the dual phone is off. So this duophone circuit has a unique feature of talking to two people simultaneously what is called three-party telephone conversation/conference facility.

Circuit Diagram of Simple Duophone System : Right Click >> View Image to view full size

The complete idea and description of this dual telephone circuit can be available by downloading this PDF document.

Pyroelectric Fire Alarm

2013-12-07T22:31:00.000+05:30

Ordinary fire alarm circuits uses diode sensors to detect fire presence. But a pyroelectric fire alarm circuit described here is an ultra-sensitive fire sensor that uses direct piezoelectric property of an ordinary piezo element to detect fire.

Circuit Diagram of : Right Click >> View Image to view full size

Sensing capability of the circuit.

The circuit of fire alarm given here is very sensitive as it uses Pyroelectric Fire Sensor . It gives a warning alarm if the room temperature increases more than 10°C which cannot be provided using a diode sensor.

The entire circuit has two sections power supply section and sensor section.
Power supply with battery backup: This section consists of a0-12V, 1A step-down transformer with a standard full-wave rectifier formed by D1 through D4 and filter capacitor C1. A battery back up is also provided in case a power failure. the diode D5 and D6 plays an important role of working the power supply as a mini ups.

Sensor side circuit: CA3130 IC based sensitive signal amplifier gives a high output when temperature near the piezo element increases. As the amplifier is a CMOS operational amplifier with gate protected p-channel MOSFETs in the inputs, it gives a quick change in the output if there is any change in the non inverting input (pin3) according to the referance voltage set by the preset VR1. When the output of the amplifier going high, it turn on the transistor T1- BC547. This makes the reset pin 12 of IC2 CD4060 to ground. From this time onwards the IC2 starts oscillating according to the oscillating components C3 and R6. Now the output Q3 of CD4060 connected to red LED2 starts flashing after a few moments. If heat near the piezo persists, Q7 (pin 14) output of IC2 becomes high after one minute, and the alarm starts beeping.

The additional advantage of this piezoelectric fire alarm circuit is that it can be connected to a solenoid pump using a relay and transistor. If a fire is detected, the solenoid pump connected to fire sensing system will spray the fire-ceasing foam or water to the possible sites of fire.

Note:

Assemble the circuit on a general purpose PCB and enclose it in a suitable case.
Connect the piezoelectric sensor (peizo element) using a thin insulated wire.
Glue the peizo element to a small piece of thin aluminum sheet to increase sensitivity.

FM Booster Circuit to Receive Far Away FM Stations

2013-12-07T22:30:00.000+05:30

This is a low cost FM booster circuit to receive far away fm stations clearly on your radio in your local area. The circuit diagram of FM booster consist of a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570.

Circuit Diagram of FM Booster : Right Click >> View Image to view full size

The output of the circuit should be directly connected to your FM receiver. Assemble the circuit on a good quality PCB and adjust the trimmers to get maxim gain.

Input Coil L1

Input coil L1 consists of four turns of 20SWG enameled copper wire (slightly space wound) over 5mm diameter former. The pin configuration of the transistor can also found on the circuit diagram.

Solar Charger Circuit For Lead acid, Ni-Cd And Li-ion Battery

2013-12-07T22:29:00.000+05:30

The solar panel based charger described here is capable of charging Lead acid, Ni-Cd And Lithium-ion batteries. This circuit diagram is designed for a solar panel which is capable of delivering 5W power. The solar panel outputs 16.5V. It can deliver a current of 300-350 mA.lead acid, Ni-Cd and Li-ion. The lead-acid batteries are commonly used in emergency lamps and UPS.

Circuit Diagram of Solar Charger : Right Click >> View Image to view full size

Working Of The Circuit

The output of the solar panel is fed through polarity protector diode 1N5402 (D1). The battery charging current can be monitored via ammeter connected in series between diode D1 and the fuse. Diode D2 is used for protection against reverse polarity in case of wrong connection of the lead-acid battery.

The circuit can charge the following type batteries with rated voltages.

A. Lead acid 12 volt battery

B. Ni-Cd 1.2V - four cell

C. Li-ON 3.6 volt Battery.

To charge a lead acid battery, shift switch S1 to ‘on’ position and use connector ‘A.’ To charge Ni-Cd cells, put switches S1 and S3 to ON position and use connector B. Note that IC 7806 act as a constant current source. Resistor R2 limits the charging current.

To cahrge LI-ON battery, shift switches S1 and S2 to ON position and use connector C. Regulator IC 7805 (IC2) provides 5V for charging the Li-ion battery.