Pan-Tilt HAT regular LED PWM connection and current limit?


#1

Hello, I just purchased a Pan-Tilt HAT from Adafruit and I’ve been unable to find any information about how exactly a person is supposed to connect regular LEDs in order to get PWM brightness control working. Also, what is the current limit for regular LEDs?

I’m not expecting my shipment for a couple of days, so I’m just making guesses based on pictures. There doesn’t appear to be anything on the HAT itself capable of switching significant current (hundreds of mA), so perhaps the “Light Data” line is intended to connect to a FET that switches the LEDs? In which case, would the current limit just be whatever doesn’t adversely affect the RPi (trip fuse or brown it out)?

FYI, I’m planning on using a NoIR camera and want to provide IR illumination. I don’t yet know how many LEDs I need in order to get sufficient illumination.

Thanks for any help.


#2

You are correct in your assessment- and yes the documentation does fall somewhat short here, I should probably fix that since I wrote the firmware for Pan-Tilt HAT so long ago now that the specifics are starting to escape me!

The Data line is, indeed, intended to connect to a FET that actually switches the lights. This is in line with how you would use any other pin on the Pi directly, so tends to be compatible with most off-the-shelf light ring products for Pi Camera- not that there are many! (I actually designed it around the regular LED version of: http://cpc.farnell.com/cyntech/lisiparoiir-01/rpi-ir-board-for-pi-camera/dp/SC13919)

The controller is actually a PIC16F1503, which can source a maximum of 25mA.

The remaining 5v power/ground connections can then supply power to your light ring as long as it doesn’t demand more power than the Pi itself- and associated power supply- can provide.