VU Meter with LED
If you are making a stereo amplifier, or if you own one already, then do not hesitate to add this circuit. The entire circuit is wired around IC4017 whose clock input is tapped through transistor BC107. Basically, IC 4017 is a 1-of-10 decade counter or a decoder.
To suggest the design, this circuit fills the gap between a simple 1-transistor sound-to-light and a unit using filter and main LEDs. But two units must be added for stereo operation.
Circuit calibration is straight forward and should present no problem. The effect of sound reaching the input is to trigger IC to count one. This means that when the music gets louder, the LEDs move faster. If you wish to use fewer LEDs, a wire must link from the next LED and should go on to reset pin 15. Note that pin 12 doesnot have any connection. To tap the input to this circuit, it is advised to tap the output from the main speakers.
If the LEDs do not move rapidly according to the music pitch, adjust VR1. If two LEDs are in parallel, the second one can be pointed towards the viewer for added effect.
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 1 KΩ
R2 = 100 KΩ
R3 = 390 Ω
VR1 = 100 KΩ
C1, C2 = 10 µF/16V
C3 = 100 µF/16V
IC1 = 4017
T1 = BC107
LED1 – LED9