DMM range and AC-DC mode Logic
This is the third circuit that you will need to build a Simple Benchtop DMM with no Microcontroller. Here the U1D and U1B 4093 acts like a de-bouncing circuit for the push keys. The 4029 counts up scrolling to binary values 00, 01, 10, 11 for the four ranges.
The binary value of 4029 is decoded to decimal by 4028 in order to light four LEDs which indicates the range or mode on the front panel. When any of these pushbuttons are pressed and held, the nand schmitt 4093 clocks to scroll the range continuously. The binary output of these counters control CMOS switches 4052 which are analog multiplexers.
The DPM or DVM gives a readout of an Analog Value or process. The Analog reading we obtain from a Circuit Measurement Jig represents some real world parameter.
In a multi-parameter instrument like DMM, the measurement jig functions and the analog signal routing is done by ganged range selection switches.
Read More here DMM range and AC-DC mode Logic