3-bit ADC that counts up, passing binary values to a DAC (resistors), then compares the DAC's level to the input signal using an opamp. When the DAC level crosses the input level, the counter stops counting, and you can see the measured value on the 7-segment display.
The counter is reset at regular intervals so a new analog signal can be converted to a digital value. Obviously, the whole process of measurement takes a long time making this one of the slowest ADCs.
