Firmware Design: Low Current LED Tricks

A project log for CoinOp Badge

Hardware badge inspired by my favorite Coin-Op video game

mike-szczysMike Szczys 07/07/2018 at 18:080 Comments

I have 22 LEDs on this board and they're powered by a CR2032 coin cell. The more current you try to pull out if this cell, the higher the internal resistance and the shorter the expected capacity.

This is a conference badge so I only really need the batteries to last about 72 hours. But even that means I can go around buring all the LEDs at once. So how do you light them all up if you can't run them all at once? By scanning the display!

I have already implemented a 1/6 duty cycle at 1kHz and I'm pulling about 28mA with all LEDs "on". Now I'm looking toward a wider design that let's me dim the LEDs as needed. Above are my sketches on this.

My solder stencil should arrive Wednesday or Thursday so I'm not doing any more assembly until then. I'll try to get all of the above implemented by then and do some battery life testing.