A panel voltmeter ammeter very cheap, can be designed using this electronic scheme that uses CMOS electronic components.
This ammeter voltmeter panel can display multiple analog inputs simultaneously (on separate displays), although using a single ADC.
IC4, the multiplexer control circuit, IC4 receives the output clock signal MSD (most significant digit) of the analog-digital converter IC1 by IC5c. Once the MSD output signal that has been converted into and directed to output, the counter is incremented, and another analog input is selected to be applied to analog-digital converter. The scheme is designed so a single switch and a single decoder BCD / 7 segment (IC2 and IC3) are activated in a certain time.
Counter is incremented when the exit into fighting disables 7-segment decoder properly. The next increment, Q4 counter resets and the cycle repeats again.
Input voltage range is from 0 to 0.999 V reference voltage and all inputs is the input pin L0of IC1's.