Decibels Meter Circuit Using LM324


Posted on Feb 7, 2014

This decibels meter circuit responds for sound pressure levels from about 60-70 dB(Decibels). That sound is picked up by an 8 ohm speaker, amplified with a transistors stage and LM324 op-amp section. For audio signal input source, a dynamic microphone can be used but a small speaker was more sensitive. The remaining three sections of the IC LM324


Decibels Meter Circuit Using LM324
Click here to download the full size of the above Circuit.

quad op-amp are used as volts comparators and drive three indicator LEDs or incandescents which are spaced about 3dB apart. An additional transistor is needed for incandescent lights as shown with the lower lamp. I used 12 volt, 50mA lamps. Each light represents about a 3dB change in sound level so that when all 3 lights are on, the sound level is about 4 times greater than the level needed to light one lamp. The sensitivity can be adjusted with the 500K pot so that one lamp comes on with a reference sound level. The other two lamps will then indicate about a 2X and 4X increase in volume. In operation, with no input, the DC voltage at pins 1, 2 and 3 of the op-amp will be about 4 volts, and the voltage on the (+) inputs to the 3 comparators (pins 5, 10, 12) will be about a half volt less due to the 1N914 diode drop. The voltage on the (-) comparator inputs will be around 5. 1 and 6. 5 which is set by the 560 and 750 ohm resistors. When an audio signal is present, the 10uF capacitor connected to the diode will charge toward the peak audio level at the op-amp output at pin 1. As the volume increases, the DC voltage on the capacitor and also (+) comparator inputs will increase and the lamp will turn on when the (+) input goes above the (-) input. As the volume decreases, the capacitor discharges through the parallel 100K resistor and the lamps go out. You can change the response time with a larger or smaller capacitor. This...




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Logic Probe with PIC12F683
Sensitive Electrostatic detector
Simulated inductor
Input-buffered-mixer
Water Flow Gauge using Arduino
SDR Soundcard Tester
CD4013 Push Button CMOS Toggle Flip Flop
Simple Lightning Detector Circuit
games timer 4
UTP cabel tester
MC1411 series Darlington current internal structure of a drive circuit
Geiger–Müller meter circuit project



Top