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If you spin another hardware revision it would be nice if the IR Tx could be moved to a PWM capable pin. Pin 12 (BCM GPIO 18) is one of the few ports that support hardware PWM, so just switching the RX and TX pins would do, and would be pretty easy as their traces run very close to each other on the board, and would be easy to manually reroute.

It would be awesome to compile some case recommendations for this hat.

Is the location of the IRRX a challenge for full-size Pi cases? Has anyone found a case that is easily moddable to acommodate the LEDs and I2C sensors? Perhaps someone has a custom 3D-printed case that fits this well?

Please do share!

I ran into in an issue with the uart passthrough from the hat. When RX on the hat is left disconnected, and UART support is enabled, there is some interference that is getting passed through as key presses. I originally discovered this using the ubuntu pi distribution, when it wouldn't boot because uboot autoboot was getting interruped by these "key presses". Either connecting the rx pin, or disabling uart support in config.txt are work arounds. To reproduce, enable_uart=1 in config.txt and connect only the tx pin and the gnd to a usb ttl serial adapter.

I'm interested in this hat, but I haven't been able to locate information on the typical range you can expect to get from it. Do you have any guide numbers for it? Thanks

I was trying to figure out what the current through the IR LEDs is, and I think that there might be a missing current limiting resistor (or two).

If I assume that the IR led is being driven at 38kHz at 50% duty, then pulse width is around 13us. The TSAL6400 datasheet indicates that limits would be ~220mA, and maybe ~1.5V? The BC817 has a Vcesat of 0.7V, so that's still ~1.3V (5V - 2*1.5V - 0.7V) unaccounted for. Working backwards ((5V - 0.7V)/2) if the LEDs were driving at 2.15V, that would draw about 900mA, which is also concerning because peak forward current is rated at 200mA (for tp/T=0.5).

Of course LED current should also be limited by the transistor (and it's hFE), but I also get stuck trying to work out what Ic for BC817 would be, because I can't figure out Ib: Vbe is typically 1.2V, but the GPIO will try and drive the pin at 3.3V, so there's approximately 2V unaccounted for there. The default pad drive current is 8mA, but that's not a limit, only a "guarantee" to drive at 3.0V if current is less than configured drive (https://www.raspberrypi.org/documentation/computers/raspberry-pi.html#voltage-specifications). It's not clear what the pad max current is, but the table lists 17mA at 2.3V, so (with an hFE of 40) Ic could be as high as 680mA.

In the worse case maybe the 5V rail is being pulled to ~3.7V while the LED is on, and the power supply is the limit? That would mean max current of ~1A, and maybe nothing on the 3.3V supply cares because 3.7V might still be enough to supply the 3.3V regulator? I don't have a scope to be able to check anything, and I don't think a multimeter will be sufficient because of the low pulse duration (and I don't want to just enable the pin to measure the steady state "on" values, because they're likely to be way over spec).

Maybe you could put references to datasheets or explicitly list their licenses if any

it could be missleading to have them in main project licensed under CC

BTW, some might not be relevant too, ie:
https://github.com/AnaviTech/anavi-infrared/blob/master/docs/25R0623.pdf