DM105 Rotary¶

This module connects two knobs, four buttons, and an OLED display to the LIN bus.

Prototype¶

The initial protoype was built on a breadboard, using an STM32C011 board from WeAct Studio, a combined rotary encoder + 2 buttons + 128x64 OLED board, and one more separate rotary encoder. All parts came from AliExpress.

This 20-pin µC has just enough pins to connect each of the two encoders to its own hardware timer. The timers are configured in "Quadrature Encoder" mode: they'll automatically handle the incoming pulses without losing track and without any CPU involvement.

A knob counts 20 pulses per revolution: only the lower 6 bits of the timer counts are used.

Each knob can be pressed as "button" and there are two more buttons, labeled "CONFIRM" and "BACK". So that's two 6-bit counts and 4 on/off buttons, for a total of 16 bits.

The plan is to have the top-left knob select a parameter and the right one its value.

LIN device¶

This module responds as slave ID 1 on the LIN bus. When queried, it sends 2 bytes:

• byte 1: right knob pressed (b7), confirm (b6), right knob position (b5..b0)
• byte 2: left knob pressed (b7), back (b6), left knob position (b5..b0)

Cable version¶

I'm constructing a more permanent setup. It includes a cable with a 2.5mm audio plug as power + LIN bus connection. This board is a bit large for an expansion base, but more importantly: when connected with a cable, these knobs can be placed where they're most convenient, away from all the breadboard jumpers.

Since LIN is indeed a bus, several such devices can be connected in parallel, as long as they each respond to a different ID.