A simple Light to Frequency Converter

Introduction.

Here is the circuit diagram of a effective light to frequency converter circuit that can be used for variety of applications such as light intensity measurement,fun etc.

The circuit is based on TLC555, the CMOS version of famous timer IC NE 555. A photo diode is used for sensing the light intensity.The timer IC is wired in astable mode.The leakage current of the reverse biased photo diode is proportional to the light intensity falling on it.This leakage current charges the capacitance C1.When the capacitor voltage reaches 2/3 of the supply voltage the out put (pin 3) goes low.As a result the capacitor discharges through photo diode .When the capacitor voltage reaches 1/3 the supply voltage the out put (pin 3) of IC goes high.This cycling continues and we get a frequency at pin 3  proportional to the light intensity falling on the photo diode.

Light to Frequency Converter Circuit Diagram & Parts List.

Light to Frequency Converter Circuit Diagram

 Notes.

§  With the given components the frequency  varies from 1KHZ @ complete darkness to  24 Khz @  bright sunlight.The frequency range can be changed by using different values for C1.

§  Use any general purpose photo diode for D1.

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Audio Distortion Meter

Description

Here is a simple 1KHz audio distortion meter that can measure the Total Harmonic Distortion (THD) on any load at any out put power.Here you have the option to select 2,4,8 or 16 Ohm loads. The circuit works by filtering the 1 kHz fundamental signal using a notch filter comprising of L1,C2,C1,R1. With a little time and calculation you can get the correct THD of your amplifier in such a simple way.

Audio Distortion Meter Circuit Diagram with Parts List .

Audio Distortion Meter Circuit Diagram

Notes

§  Inductor L1 is a UTC VC 15 variable inductor.If this is not available try with any kind of variable inductor you have.

§  Load resistors R1 to R4 must be rated at least twice the power you are going to deal.

§  Meter M1 shall be a general purpose AC voltmeter with range determined by the maximum possible output voltage of the Amplifier under test.

§  Feed the input of your amplifier a 1KHz signal from a signal generator.If you don’t have a signal generator make a 1 kHz Colpitts oscillator for the purpose.

§  Connect the out put of Amp to points P1 and P2 of the circuit.

§  First select the required load resistance using S1 .

§  Slide the switch S2 to CAL position (to left as in circuit) .

§  Note the reading on the AC meter as V cal.

§  Now slide S2 to THD position (right) .

§  Adjust L1 and R5 to get the minimum meter reading and note that reading as V min.

§  Now THD(%) = ( V min / V cal ) *100.

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Audio level meter circuit

Description

A simple and low cost audio level meter circuit that can be used to measure the audio level of your sound source.This circuit is a valuable tool for those who are interested in audio circuits.

The circuit is designed with a flat frequency response in the range of  20Hz to  50Khz. Input sensitivity is 100mV for a FSD on a 100uA ammeter.The circuit is build based on on two common emitter amplifiers, the first stage has a preset resistor R3 (1K) which may be adjusted for a FSD. The last stage is biased to operate at about 1/2  the supply voltage for maximum AC voltage deflection. C2&C2  (10 uF) acts as a filters through which audio frequencies  are passed .  The full wave bridge rectifier converts the signal to a varying dc voltage. The meter will show this voltage as the output reading which is proportional to the input voltage level.

Audio Level Meter Circuit Diagram with Parts List

Notes.

§  The meter reading is instantaneous and it will not provide you with a peak to peak reading.

§  To calibrate the meter, provide a  1Khz 100mV sine wave at the input and  adjust R3 to get a full scale reading on the meter.

§  Use a well regulated & filtered 12 V supply for powering the circuit.

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Audio Wattmeter Circuit

Description

This is an easy trick to measure the output of an amplifier.Here resistor R2 acts as the load for for the amp and it should be able to withstand twice the maximum power of the amp you are going to measure.The meter scale must be calibrated and with a little effort you can get good results.

Audio Watt meter Circuit Diagram with Parts List.

Audio Wattmeter Circuit Diagram

Notes

§  If 1A bridge is not available , make one with four 1N 4007  Diodes.

§  The resistor R2 must be twice the power of amp you are going to measure.

§  To calibrate  the device, Connect the output of amplifier to to port 1.Also connect a AC voltmeter to port1.

§  Set R1 fully off.That means full counter clockwise direction if wired conventionally.

§  Adjust the output of amp to read 20Volt rms on voltmeter.This is the equivalent of 50W on 8 Ohm  load.

§  Adjust R1 for a full scale deflection on meter M1. Now fix the wiper of preset R1 using some super glue.

Now reduce the voltage across the port 1 by reducing the output power of amplifier under test  according to the table given below and mark the readings on the meter scale.The device is ready to measure.

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Lamp Flasher Circuit using NE 555

Description

This is the circuit diagram of lamp flasher operated from mains. By this you can flash up to 200 Watt lamps at rates determined by you. IC NE555 is wired as an astable multivibrator for producing the pulses for flashing the lamp. The flashing rate can be set by the value of resistors R2 & R3.

Diodes D1 & D2 provides a half wave rectified regulated supply for the IC. Transistor T1 is used to drive triac and triac BT136 for driving the load. Resistor R4 limits the base current of Q1.

Flashing Circuit Diagram & Parts List

Notes

§  Assemble the circuit on a good quality PCB or common board.

§  Connect a 100K pot instead of R2 if you need frequent changes in rate.

§  Many parts of the circuit are live with potential shock hazards. So please be careful.

§  As usual use an IC holder for mounting the IC.

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Hi Fi Amplifier Circuit – 2X12 Watts

Description.

Here is the circuit of a 2X12 watt Hi Fi amplifier circuit using IC TDA 2616 from Phillips. A quiet simple and robust circuit using very less components. This makes the circuit ideal for a portable power amplifier. The circuit delivers 12 Watts power on 8 Ohm speaker for each channel at +/- 12 V dual supply.

The TDA2616 is a stereo power amplifier IC comes in a 9-lead single-in-line (SIL9) plastic power package (SOT131). This IC is  specially designed for mains fed amplifier circuits, such as stereo radio, tape  and television .The IC has good gain balance of both channels and Hi-fi in accordance with IEC 268 and DIN 45500 standards. Also the IC TDA 2616 has special inbuilt circuit for the suppression of noise signals at the inputs, during switch-on and switch-off. This prevents click sounds during power on and power off.

Hi Fi Amplifier Circuit Diagram with Parts List.

Hi Fi Amplifier Circuit Diagram

Notes.

§  All capacitors except C10 & C9 are ceramic.

§  All capacitors must be rated 50V.

§  Use a well regulated and filtered +/- 12 V dual power supply that is able to provide at least 2 A continuous current.

 TDA 2616 PIN Diagram and Configuration

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High & Low voltage cut-off with delay& alarm

Description.

This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used to make a automatic voltage stabilizer.

When the mains voltage is in the normal level, the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts. At this condition transistor T1 will not conduct. The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting. The relay will be activated and the green LED will be glowing.

When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of D4 is greater than 5.6 V. At the same time transistor T2 will be non conducting which results in the deactivation of relay to cut the mains supply from load. When the mains voltage is less than the set limit transistors T1 & T2 becomes non conducting making the relay to de-activate and cut the load from mains.

The timer NE555 is wired as a monostable multivibrator with a pulse width of 10ms.When the power comes back after a cut off a negative voltage is obtained at the trigger pin which triggers the IC NE555. The transistor T3 gets forward biased and it drives the buzzer to produce a beep as an indication of power resumption. Also the transistor T1 is made on which in turn makes T2 off. As a result the relay will remain de- activate for 10ms and this provides the sufficient delay and the equipment is protected from surge voltages.

Circuit diagram with Parts list. Click to enlarge.

Notes.

§  To calibrate the circuit a autotransformer is needed. Connect the output of autotransformer to the transformer primary.

§  Set the voltage to 260V and adjust VR1 to make the relay deactivated.

§  Now set the autotransformer to 160V and adjust VR2 so that the relay is de-energized.

§  VR3 can be used to vary the volume of buzzer.

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InfraRed (IR) Sensor/Detector Circuit

Description.

The circuit shows that the output of IC1 555 IC, which is designed for a duty cycle of 0.8mSec,with a frequency of 120Hz and 300 mA peak current, is used to drive the infrared LED,D1.From the connection it is clear that the diodes D1 and D2 are on the same line, just a few centimeters apart, on the breadboard. Thus diode D2 receives the infra-red output from the diode D1.The diode signal, which is given to the inverting terminal of the op-amp IC LM 358 gets amplified and its peak is detected by diode D4 and capacitor C4.The forward voltage produced by diode D4 is compensated by diode D3 with R5 and R6.According to the distance between the infra-red transmitter and receiver, a proportional DC voltage is fed to the inverting input of IC2.According to the output of the comparator the LED is turned ON and OFF and this is detected by the transistor Q1.Thus the relay is driven according to the output of Q1.The comparator output is set according to the value of the pot.

This circuit is mainly used for liquid level detection or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. The biggest advantage of this circuit is that there is no physical contact with the liquid whose level is to be measured. The range is set by adjusting the pot. Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device’s sensitivity.

Notes.

Use a good quality regulated power supply .The sensor diodes must not be subjected directly to other light sources.

Parts List.

1.       Resistance R1                       10K(4W)

2.      Resistance R2,R5,R6,R9     1K(4W)

3.      Resistance R3                       33R(4W)

4.      Resistance R4,R8                 1M(4W)

5.      Trimmer Cermet R7           10K

6.      Resistance R10                    22K(4W)

7.      Capacitance C1,C4              1 uF(63V)

8.      Capacitance C2                   47pF(63V)

9.      Capacitance C3,C5,C6      100uF(25V)

10.   Diode D1                             IR LED

11.    Diode D2                             IR Photo-Diode

12.   Diode D3,D4                       1N4148(75W/150mA)

13.   Diode D5                             LED

14.   Diode D6,D7                      1N 4002

15.   PNP Transistor Q1           BC 558(45V/800mA)

16.   Timer IC IC1                     NE 555

17.   IC 2                                     LM358

18.   IC 3                                     7812

19.   Relay                                  SPDT(2A/220V)

20.  J1                                        Two ways output socket

Infrared Sensor Circuit Diagram.

Check out our Industrial Circuits category for more circuit applications.

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Lead acid battery charger circuit

Description

Here is a lead acid battery charger circuit using IC LM 317.The IC here provides the correct charging voltage for the battery. A battery must be charged with 1/10 its Ah value. This charging circuit is designed based on this fact. The charging current for the battery is controlled by Q1, R1, R4 and R5. Potentiometer R5 can be used to set the charging current. As the battery gets charged the current through R1 increases .This changes the conduction of Q1.Since collector of Q1 is connected to adjust pin of IC LM 317 the voltage at the output of LM 317 increases. When battery is fully charged charger circuit reduces the charging current and this mode is called trickle charging mode.

Battery Charger Circuit Diagram with Parts List.

Lead Acid Battery Charger Circuit Diagram

Notes .

§  Connect a battery to the circuit in series with a ammeter. Now adjust R5 to get the required charging current. Charging current = (1/10)*Ah value of battery.

§  Input to the IC must be at least 18V for getting proper charging voltage at the output .Take a look at the data sheet of LM 317 for better understanding.

§  Fix LM317 with a heat sink.

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Light activated switch circuit

Description.

This is the circuit diagram of a light activated switch based on National Semiconductors comparator IC LM 311 and a LDR.

The circuit is based on a voltage comparator circuit wired around IC 1.The non inverting in put of IC1 is given with a reference voltage of 6V using resistors R3 and R4. The input to the inverting input will be the voltage across the LDR that is light dependent. At darkness the resistance of the LDR will be high and so do the voltage across it. At this condition the voltage at the inverting input will be higher than the reference at non inverting pin and the out put of the comparator will be low(~o V). When the LDR is illuminated, its resistance drops and so do the voltage across it. Now the voltage at inverting input will be lower than that at non inverting input and the out put of the comparator goes high (~12 V). This makes transistor Q1 on and it drives the relay. As a result we get a relay switching according to the intensity of the light falling on the LDR.

Light Activated Switch Circuit Diagram with Parts List .

Light Activated Switch Circuit Diagram

Notes.

§  Adjust POT R1 to set the desired light intensity for switching the relay. For this illuminate the LDR with the desire intensity light. The relay will be either on or off. Adjust POT R1 slowly so that the state of the relay changes. That’s it. Now the circuit is set for the given intensity of light.

§  Assemble the circuit on a good quality PCB or common board.

§  You can use either a 12 V battery or a well regulated & filtered 12V DC mains operated power supply.

§  The pin 5&6 (Balance & Balance/Strobe ) of IC LM311 are shorted to minimize the chance of oscillations.

§  The pin out of LM311 is also given together with the circuit diagram.

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Low cost fire alarm circuit.

Description.

When there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact.

Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC 128). So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie, light, bell, horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched.

Circuit diagram with Parts list.

Notes.

§  The Preset R1 can be used to desired temperature level for setting the alarm ON.

§  This is not a latching alarm, that is; when the temperature in the vicinity of the sensor decreases below the set point the alarm stops.

§  The circuit can be powered using a 9V battery or a 9V battery eliminator.

§  All capacitors are electrolytic and must be rated at least 10V.

§  The load can be connected through the C, NC, NO points of the relay according to your need.

The calibration can be done using a soldering iron, and a thermo meter. Switch ON the power supply. Keep the tip of soldering iron near to the Q1. Same time also keep the thermometer close to it. When the temperature reaches your desired value adjust R1 so that relay gets ON. Done!

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