Unicorn HAT extension for more LEDs


#1

I just bought a reel of WS2812 LEDs and I would like to use the Unicorn HAT to drive them, since it contains the 3.3 to 5V level converter and an EEPROM. There are connections on the board for Vcc,Din,Gnd. Are these at the start or end of the chain? If at the start, is there any way to turn off the HAT LEDs, even if it requires drilling through the board at an appropriate point? A circuit diagram would be helpful here.

Tony


#2

Hi Tony,

Those breakout pins on Unicorn HAT are a bit odd really. They let you feed in data from another source, so they would let you drive Unicorn HAT from an Arduino, for example.

Wrecking a Unicorn HAT to drive your WS2812s would seem a shame. A much simpler way would be to drive them directly off the Pi’s GPIO. You could even use the same data pin and then use our Unicorn HAT library to control them. You would, as you say, ideally need a logic level converter, but they’re only a couple of quid, so waaaaay cheaper than a Unicorn HAT. We suspect that they might run just fine at 3.3V though, so it’s worth trying that first.

Hope that helps :-)


#3

Hi Sandy

Thanks for the speedy reply. If I use a separate level converter, will I still have access to the libraries as for the Unicorn and same start up with the HAT EEPROM not present?
I did some reverse engineering on the HAT and see now that the breakout pin DIN is directly connected to GPIO18, pin 12, and the input of the SN74LV1T34 level converter IC. So with the HAT disconnected from the Pi, that pin is indeed an input to the board.

Tony


#4

the lack of EEPROM to your setup should have no adverse effect, it is merely used to default the layout to 8x8 (as opposed to 4x8 for the pHAT)… that is something that you will need to override or ignore for your own needs anyhow.