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Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

May 25th, 2010

LED Based Car Battery Voltmeter

Circuit Description

Here is a simple car battery voltmeter circuit using LEDs that can be easily installed in cars. This circuit consists of four LEDs and a quad operational amplifier IC LM 324 as its main part. This circuit is meant for displaying the output voltage of the car battery in a LED dot display format.

The four operational amplifiers in IC LM 324 is used here as comparators. The inverting input pins (pins 2, 6, 9, 13) are kept at reference voltages 5.6V, 5.2V, 4.8V, and 4.4V respectively by using zener diode D1and resistors R3, R4, R5, and R6 as shown in the circuit diagram. The battery voltage is given to the non inverting inputs of comparators through voltage divider network consisting of resistors R1 and R7. According to the level of voltage the output of comparators go high and hence the corresponding LEDs will glow.

Circuit Diagram

LED Based Car Battery Voltmeter

LED Based Car Battery Voltmeter

Notes

  • Use a good quality PCB to assemble this circuit.
  • Use common power supply for 4 op amps in IC LM 324.
  • Adjust potentiometer R6 and make sure that required voltages are available at the inverting pins.
  • Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit.
May 25th, 2010

Simple Metal Detector Circuit

Circuit Description

The circuit diagram of cost effective metal detector has been published here. This circuit and an old pocket radio constitute a simple metal detector device. This circuit is a Colpits oscillator circuit is operating at medium frequency band. The radio and the circuit are placed close to each other. Radio is tuned to the same frequency of the circuit. At this condition there will be no sound from radio since their frequencies are matched and cancel each other. This is the final arrangement of metal detector.

If a metal object is placed near this circuit, the inductance of the coil changes. By the effect of this, frequency of oscillation of oscillator changes and a mismatch in frequency occurs between the circuit and radio. This change inductance is utilized here to detect metals. When mismatch occurs, radio produces hissing sound and metal is detected.

Circuit Diagram

Simple Metal Detector Circuit

Simple Metal Detector Circuit

Notes

  • To make L1 make 60 turns of 36SWG enameled Copper wire on a 1 cm PVC tube.
  • Powering the circuit using an adapter rather than a battery induces noise. It is better to use battery for powering radio projects since it reduces noise.
  • Radio for metal detector can be an old pocket radio.
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