Analog to Digital Converter

This 4-Bit Analog to Digital converter was done to challenge my analog and digital electronic design skills.

The input is a voltage from 0-9 V controlled with a voltage divider made using a potentiometer and a resistor.

When the switch is flipped it enables the 555 timer which pulses the clock input of the CD4520 CMOS Counter. The output of this counter is connected to a Digital to Analog converter built using transistors. The 555 timer will cause the counter to increase in value, driving the voltage of the DAC higher until it matches the input voltage. This causes the OpAmp to stop the timer. The value is displayed in binary on an LED Bar Graph.