Adafruit LED Matrix Driver


#1

I’m looking for a 128 LED matrix driver and came across the following by Adafruit:

Pimoroni only stock the latter, but as far as I tell these are identical, and seem to work from 3V to 5V depending on what LEDs you have attached. (I’m going to homebrew my own ‘matrix’).

Anyone know if that’s the case?

I notice the same chip is used in:

But I suspect Pimoroni have level shifted the I2C - which I’d probably end up doing for safety.

Cheers,
Tom


#2

Just saw this new product on Adafruit, https://www.adafruit.com/product/3211 Adafruit RGB Matrix Bonnet for Raspberry Pi. Onboard level shifters, power protection etc. Not in stock yet though.


#3

I did see the older version of that product in my travels, but both come with the caveat:

Please note: this Bonnet is only for use with HUB75 type RGB matrices. Not for use with NeoPixel, DotStar, or other ‘addressable’ LEDs.

Which makes me think my homebrew ‘matrix’ might not be suitable.


#4

Ah, Ok, only took a quick look, missed that part. I haven’t tackled a project like that my self. Was looking at the new products and remembered reading your post.


#5

My understanding (albeit limited being a software engineer) is that the driver puts out constant(ish) current at 25mA - so as long as the LEDs in my matrix are happy with that and wired correctly, then I should be fine.


#6

The only LED matrix’s I’ve used are the one on my Sense Hat and BBC Micros Bit. The hardware is all done for me, just have to code up my Python file. Only other stuff I’ve played with is Neo Pixel on my BBC Micro Bit. A Micro Pixel Edge board. Same deal only had to mess with the coding side of things. Did have to be careful of the brightness / current draw on the Micro Bit though. On battery its fine, when powered by USB you have watch it though, it’s onboard 3V regulator is limited in the current it can supply. It’s really only meant for powering it while programing it… Neo Pixels can draw quit a bit of current when on a high brightness.


#7

Yeah, I’m going for something a little bit more bespoke and I’m in the process of designing my own modular LED PCBs - fun stuff.


#8

Sounds interesting, I hope it all works out OK for you. No magic blue smoke etc.


#9

It’s mainly trying to design a set of PCBs such that they take advantage of the cost & quantity of PCBs you get from places like OSHPark. Interesting challenge in itself.

It’s a board that I could design as a whole, but given the size it’d be expensive, I’d end up with 3 of them (more than I want) and I’d get hit for customs charges.

If I make it modular, I can cut the cost by about a third, end up with just one board (once they’re joined) and avoid import charges in one fell swoop!


#10

Back to the HT16K33, different question this time. The datasheet specifies two different typical row source currents depending on different conditions (VDD-2V & VDD-3V). I presume the 2V or 3V depends on the LED?

I don’t suppose anyone at Pimoroni might be able to help me understand how the source current is actually determined. Do I just hook up my LEDs and hope for the best?