Here is the circuit diagram of stereo digital volume control. This circuit could possibly be applied for upgrading your manual volume management within a stereo amplifier circuit. In this particular circuit, push-to-on switch S1 controls the forward (volume enhance) operation of the two channels while a identical switch S2 controls reverse (volume reduce) operation of the two channels. In this digital volume control circuit, the IC1 timer 555 is set up as an astable flip-flop to deliver low-frequency pulses to up/down clock input pins of pre-setable up/down counter 74LS193 (IC2) through push-to-on switches S1 and S2. To adjust the pulse width of pulses from IC1, you may possibly replace the timing resistor R1 by using a variable resistor. This is the figure of the circuit;
Operation of switch S1 (up) triggers the binary output to increment while operation of S2 (down) triggers the binary output to decrement. The highest count being 15 (all outputs logic 1) and lowest count being 0 (all outputs logic 0), it outcomes in highest and lowest volume respectively. The active high outputs A, B, C and D of the counter are utilized for controlling two quad bi-polar analogue switches in each of the two CD4066 ICs (IC3 and IC4). The two of the output bits, when high, short a part of the resistor network comprising series resistors R6 thru R9 for one channel and R10 thru R13 for the other channel, and thus manage the output of the audio signals being fed towards the inputs of stereo amplifier circuit module. Push-to-on switch S3 is utilized for resetting the output of counter to 0000, and thus turning the volume of both of those channels to the lowest level.
