Circuit controls brightness of multiple displays

摘要

I recently needed to control nine seven-segment displays for a micro-controller's serial port. The complication I faced was the need to provide a continuous brightness adjustment for all the digits-from completely dark to fully bright. I couldn't easily use the obvious solution of a string of 74HC595 serial-to-parallel converters driving the segments through series resistors, because I would have needed a variable power supply for the displays-an inefficient and inelegant approach. I considered using software to control the duty cycle of the displays' drive signal, but as a long-time analog-circuits guy, I felt honor-bound to find a way that wouldn't require writing any more code.