Seven segment display circuit with the 4511 decoder and the 4029 counter


These seven segment displays (I used to call them LED digits) are everywhere. Fortunately, they're very easy to drive. I had a MAN74A, which has two common cathodes, and seven input pins - one for each of the segments. The seven inputs are provided by a really smart IC called 4511, BCD (Binary Coded Decimal) decoder. The 4511 takes in a 4-bit BCD number and outputs on seven pins in such a way that the MAN74A will display the proper digit.

The 4-bit BCD number is provided by a 4029 chip, which is a binary/decade counter. What this means is that it counts up or down on four output pins, either between 0 and 15, or between 0 and 9 (which is used here), whenever there's a pulse on its clock input pin.

As expected, the clock pulses are provided by a 555 timer chip operating in astable mode.

In short, [555 generates clock pulses periodically] -> [4029 counts up and outputs a 4-bit BCD number] -> [4511 converts from BCD to MAN74A's input] -> [MAN74A's LED segments come on].

Circuit diagram



MAN74A reference diagram