With tonight's checkin, you can use a potentiometer on a Pi to control the speed of an engine/train. As the Raspberry Pi is a digital device, and by their nature, potentiometers (rheostats) are analog devices, you need to purchase a some additional hardware to make this all work. Specifically, you need a MCP3008 analog to digital chip (available at Amazon at 2 for $14) to convert the analog output of the pot to a digital value the Pi can work with. The chip allows up to 8 pots to be connected to it at a time, BTW.
Below is a picture of my Pi and a development breadboard, which makes prototyping much simpler. The interesting bits are the little black chip (circled in red below), and the pot (the thing to the lower left of the black chip). The chip is the MCP3008. It takes the analog value from the pot (a voltage from 0 to 3.3), and maps it into a float value between 0.0 and 1.0. This value is then scaled from 0 to 199 (for TMCC2/Legacy engines) or 0 to 31 (for TMCC1 engines).
Here's the Python code to make this work (controls the speed of a TMCC1 engine with the ID of #1:
GpioHandler.when_pot(TMCC1EngineCommandDef.ABSOLUTE_SPEED, 1)
Of course, you can also use this command in client-server mode:
GpioHandler.when_pot(TMCC1EngineCommandDef.ABSOLUTE_SPEED, 1, server='192.168.3.35')
This code sends the speed changing commands to a TrainController server running on 192.168.3.35.
-- Dave
