Created by
Created March 25, 2012
Last modified May 15, 2012
Tags 311   7-segment-display   7414   7447   7490   de-bounce   digital   led   phototransitor   schmitt-trigger  


A possibly complete light sensitive counting circuit with 3 digits making use of 311, 7414, 7490, and 7447 ICs and 7-segment displays.


This is a light sensitive counting circuit but may not be complete/functional.

This circuit is based upon the work by Richard & Sam as posted in their Youtube video in 2011 at

I want to build this circuit to track the number of times a train (and its cars) traverses a particular segment of track on my model railroad. Things I need to determine are resistor and capacitor values, whether 5v is suitable, or if 12v or greater is necessary, whether I have power applied properly (supply and ground).

I've recently made changes to the displays, realizing that I should be using common anode displays. Also learned about de-bouncing switches and have applied a capacitor and a schmitt trigger. I believe I'm far enough along to try to assemble this on a breadboard to see what I can get to work. Please leave your comments below if you have any insight on what may or may not work here.


Revision 8: Sent common on the 7 segment displays to ground/negative

Revision 9: I've added more connections to the 7490s: QD to 7447, QA to Input 2, Resets to Ground/Negative

by lucasmoten
March 25, 2012

The alternate, single digit variety I have working. I still need to update this diagram, but until then you might want to check out

by lucasmoten
May 15, 2012

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