Does the Unicorn Hat require an external power supply?


#1

Hello, My question is does the Unicorn Hat require an external power supply to run? I have a 5V DC with 2.1 A output adapter connected to the Raspberry Pi. Is that enough or does it need more of a power output to run?


#2

it takes power from the GPIO header on the Pi. You’ll be fine with a 2A PSU.


#3

Are you sure?

20mA per LED colour gives me 60mA per LED. 64x60mA equals more than 3.6A


#4

Yes, I’m sure… you don’t want to run the LEDs full beam. In fact the last soul who tried that ended up with a bunch of components desoldering themselves from the board ;-)


#5

IMO this limitation should be mentioned/described somewhere (especially since heat dissipation is an issue as well). Probably not a critical issue for the reason you gave but still something to keep in mind.


#6

The most recent library limits the brightness to 50%, so unless you modify it then there’s simply no risk of running into either power or heat dissipation issue.

Of course this is a cap in the software we provide, if writing your own then you’d have to consider what is sane or not sane to do.


#7

Hi RogueM,
I’ve noticed my LEDs are nowhere near as bright as they used to be before an update. How do I go about modifying the library so I can get back to the original brightness?
Thank you!


#8

First of all, verify that your scripts don’t include a brightness setting… if so remove it or raise it (max value 1.0).

If that’s still not enough for you then have a look at the brightness method in unicornhat.py, it should be self-explanatory… however there is a reason we now reign the brightness back, use common sense, i.e don’t look to the LEDs directly, use a diffuser, etc… eye injuries is not a matter to take lightly!


#9

Thanks RogueM! I edited the unicornhat.py as you suggested–it now works like it used to.