I finally finished this project of an external display for racechrono using two 3.5 inch screens and an ESP32.
I find the interface of racechrono hard to read at a glance when driving, even with a customized layout, so I made my own instead of complaining.https://github.com/APatenaude/rc-diy-remote-display-esp32
It turned out better than I expected and being able to test using asseto corsa is the one thing that made this possible.
There is one problem I encountered with the speed reported by the monitoring api.
I have to apply a ~3.6 multiplier to the values returned for both speed and delta speed for them to match my actual speed.
For the equation "channel(device(gps), speed)*10", I need to apply a 0.36 multiplier and for "channel(device(gps), delta_speed)*100" I need to apply a 0.036 multiplier. The exact value seems to be around 3.62 to 3.65, hard to tell with all the rounding that might be going on.
This is true both when testing with asseto corsa and when testing with my custom gps. I tried to reset the app thinking it might be a setting I'm missing but that doesn't seem to be the case. Note that the speed displayed in racechrono is correct, just the value returned by the monitoring api is wrong.