[mythtv-users] I know this isn't a hardware forum, but...

[Stephen Worthington]

On Sat, 29 Jun 2019 01:17:52 -0400, you wrote:

>I was wondering if anyone has tried to connect the GPIO pins of a Rpi
>to the IR receiver input on a IR repeater?  The pinout for the receiver
>port has +12V, signal and GND.  The GPIO ports on the Rpi are +3.3V.
>
>I figure this should involve connecting an NPN transistor in the
>circuit so that the GPIO pin can switch the transistor to send +12V to
>the signal pin but I cannot find an example of such a circuit with two
>separate GND (IR repeater and Rpi).  Can I just tie the GND pins
>together and have the GPIO, +12V and GND tie to the transistor pins (B,
>C, E respectively with signal also tied to C)?  Would I need more than
>just the transistor and a resistor or two (1K?? on the GPIO and maybe
>100?? on +12v)?
>
>My goal is to have the Rpi emulate an Alexa device (using fauxmo) and
>send fake IR signals (using LIRC?) to the repeater to control my
>devices (STB, BD, etc.) through voice control.  Best idea I could come
>up with for STBs that don't support Alexa.
>
>TIA!

I think in theory you are right that you can just use a transistor to
do the job, but normally if you are doing a level shift these days,
you use a level shifter chip.  There are plenty out there to choose
from.

https://www.raspberrypi-spy.co.uk/2018/09/using-a-level-shifter-with-the-raspberry-pi-gpio/

But if you get the hardware working, what software are you going to
use?  You would need to write a driver for your hardware.

The simple way to do this would be to plug in a USB 2 IR
transmitter/receiver.  If you get one with Linux drivers, then it all
should just work.  One that is MCE compatible and does both RC-6 and
RC-5 protocols would cover the largest number of remotes if you want a
remote input as well, and they often have a transmitter option (make
sure to choose one that says it does).