If you're using the Sonic Pad or Klipper you may be able to define a code macros named T0, T1, T2, and T3 with something like an M117 command (just display a message to the console). Then it would just treat the Tx commands as a macro that just prints a message.

I'll give that a shot. Thank you!

I can confirm that the relay listed above works perfectly with the programming header (PA13) pin on the Ender 3 S1 main board and the 3d Chameleon! Now to get my GCode setup to print with it!

Perfect! That give me some direction to safely experiment. Thank you!

Just adding some data to this thread for others. For the Ender 3 S1 / S1 Pro, it looks like the following pins might work. I'm still trying to understand if I need to use a relay to isolate the printer from the 3dChameleon or something simliar. I'm also concerned will the voltages match between the two. Based on the klipper config that's included with the Sonic Pad, PA15 is the unused z end stop signal pin. Based on this website (https://support.th3dstudio.com/helpcenter/ezneo-creality-v2451_301-ender-3-s1-board-setup/) PA13 and PA14 might be available on a programming header (see link for location).

Josh- Did you happen to get your Ender 3 S1 with Klipper working with the I/O pin? Did you use a relay or anything to connect the 3dChameleon to the printer's mainboard? What I/O pin did you use? I just ordered a 3dChameleon for my Ender 3 S1 with Sonic Pad and was hoping to use an I/O pin right away instead of the switch. --Ben