Step 5 - Fixing the ALU and Building the Program Counter

A project log for SAP 1 Computer on Printed Circuit Boards

Inspired by the video series by Ben Eater, I am developing a set of printed circuit boards for the simple as possible computer.

tomtibbettstomtibbetts 04/07/2018 at 22:040 Comments

My latest video can now be found on YouTube: 

I have validated that the issues I was having with the zero detect circuit was caused by the logic levels being pulled down by the LEDS on the output of the ALU.  I went ahead and replaced the LEDs with a small circuit board populated by an ULN2803 darlington transistor array to drive the LEDs.  This solved that problem.

Otherwise, I have built the program counter and it works with no issues.  The circuit for it is below.