TL;DR: LEDs when 'on' are great, however, they're too bright when they should be 'off'.
I'm trying to build a custom, large 7-segment LED display driven by a Raspberry Pi. I'm a coder so the bit twiddling is the easy bit (although I'm very willing to believe I've screwed that up too :)), electronics ... not so much.
I'll eventually be using 21 LEDs per segment of the digit, split into 3 strings of 7 LEDs, so I need about 24V DC to power the LEDs.
I thought of using an MIC5891 in each of the digits because it promises latching, easy serial input with 5V logic supply, chaining and 'will sustain at least 35V in the on-state'.
Here's what my test board looks like:
All 'off' and the LEDs are very dim (about 1V) but acceptable.
If any of the 'segments' are lit, the ones which should be off are showing and I can record about 6v across them, so they're pretty bright :(
Just for my sanity here's the 21 LED segment setup.
I wonder if there's a grounding issue here, I keep seeing mention of pull-down resistors but always in the context of inputs.
Any advice very welcome -- it's driving me nuts :(