3 LED BATTERY MONITOR

1. This is the circuit diagram of a 3 LED bar graph type battery monitor circuit that is ideal for monitoring the voltage level of an automobile battery.
2. When battery voltage is 11.5V or less transistor Q1 will be On and the LED D1 will be glowing.
3.  When battery voltage is between 11.5 and 13.5V, the transistor Q2 will be On and the LED D2 will be glowing.
4.  When battery voltage is above 13.5V the transistor Q3 will be On and the LED D7 will be glowing.

NOTES:

• Assemble the circuit on a general purpose PCB.
• The battery to be monitored can be connected between the terminals namely A and B.
• It is always better to use LEDs of different colour.

12V-15A VOLTAGE REGULATOR CIRCUIT

1. Here is the circuit diagram of a powerful 12V regulator that can deliver up to 15 A of current.
2. The common voltage regulator IC 7812(IC1) is used to keep the voltage at steady 12V and three TIP 2599 power transistors in parallel are wired in series pass mode to boost the output current.
3. The 7812 can provide only up to 1A and rest of the current is supplied by the series pass transistors.
4. The 15A bridge B1 does the job of rectifying the stepped down AC input. The capacitor C1, C2 and C3 act as filters.
5. The 1A fuse F1 protects the IC1 from over current in case if the pass transistors fail. The 15A fuse F2 protects the entire circuit (especially the pass transistors) from over current.

NOTES:

• Assemble the circuit on a good quality PCB.
• The T1 can be a 230V AC primary, 18V secondary, 15A type transformer.
• The B1 can be a 15A bridge.
• If 15A Bridge is not available, make one using four RURG1520CC diodes.
• The IC1 and transistors must be mounted on heat sink.

CAR STEREO AMPLIFIER CIRCUIT

1. Here is the circuit of a car stereo amplifier based on TDA1553. TDA1553 is a monolithic Class-B audio amplifier which contains 2 x 22 watt amplifiers in bridge tied load configuration.
2. The amplifier operates from 12V DC and is developed intentionaly for car audio applications.
3. The IC also has a load of good features like short circuit protection, load dump protection, reverse polarity protection, loud speaker protection etc.
4. In the circuit , C5 and C4 are input decoupling capacitors while C3 sets the delay time for loud speaker protection.
5. C1 and C2 are power supply filter capacitors.

   
   

   
   

   
   

   
   

   NOTES:
   

   • Assemble the circuit on a good quality PCB.
   • Use 12V DC for powering the circuit.
   • The circuit can deliver 22W per channel into 4 ohm speakers.
   • Fit the IC with a proper heat sink.

   
   

AUDIO LEVEL METER CIRCUIT

1. 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.
2. The circuit is designed with a flat frequency response in the range of  20Hz to  50Khz.
3. nput 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.
4. 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
5. The meter will show this voltage as the output reading which is proportional to the input voltage level.

   
   

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.

LED RAMPING CIRCUIT

1. In this circuit the intensity of LED will vary in a ramping fashion. 
2. The circuit consists of three ICs: Two 555 timer ICs and one LM393 op-amp.
3. IC1 and IC2 are wired as oscillators to produce 10 KHz and 1 Hz frequencies respectively.
4. These two frequencies are given to the inputs of the op-amp LM393.LM393 is wired as a comparator and its output will be a PWM signal
5. This PWM signals controls the FET Q1 to drive the LED. The LED will rise from OFF state to full brightness slowly and then slowly fades to OFF state and this operation repeats.
6. The resistor R4 controls current through the LED.

   
   

NOTES:

• Assemble the circuit on a general purpose PCB.
• The ICs must be mounted on holders.
• The power supply for this circuit can be anything between 3 to 12V.
• I recommend 6V for this circuit.
• The effect can be varied by changing the values of C1, C2, R1 or R2.