Circuit controls brightness of multiple displays

Posted on Sep 12, 2012

I recently needed to control nine seven-segment displays for a microcontroller`s serial port. The complication I faced was the need to provide a continuous brightness adjustment for all the digitsfrom 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 displaysan 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. Besides, I`d used up all the I/O pins

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