This autoscaling vumeter circuit is very simple VU meter that uses only 16 LEDs and may indicate 74 signal levels making it very useful peak detector.
The input signal of this autoscaling vumeter circuit is amplified by A17 (10 -5 to 100 times, depending on setting of P2) and picked up by D18. Therefore, the voltage on C1 is equal to the redressed peak input signal. This voltage is applied to the noninverting input of comparators A1 + A16. To comparators A1 A8 is applied a fixed reference voltage, which is taken from the supply voltage through the voltage divider formed by resistors R1 and R8 P1.
Outputs of A1 + A8 + control LEDs D1 and D8 connected to inputs of IC1. This circuit is an 8-bit priority encoder that converts the digital code from D0 - D7 inputs in a 3 bit number Q0 + Q2. This binary number is used to control an double 8-channel multiplexer, IC2.
Because input multiplexing stages applies reference voltage of the first eight comparator reference level of the second set of eight comparators is automatically adapted to input signal level.
Depending on the input signal, some of the LEDs D1 - D8, or all, will lit. Side consists of D9 + D16 shares the next level of voltage (one-eighth scale) in eight sections. The advantage of this configuration is that the resolution is practically independent of the input signal and is maintained within acceptable even at low input levels.