README.md

# TMC2209 Xiao RP2040 stepper

This is a stepper controller based on a xiao RP2040 communicating with a TMC2209 driver. One interesting application is using Stallguard for sensorless homing:

![](video/homing.mp4)

## Design

Jake designed this board in EAGLE with the following in mind:

- The TMC2209 has an internal regulator that needs to be bypassed when feeding it only 5V. A resistor of 10R must be added for this.
- TX and RX pins are connected with a 10k resistor, with RX going to the PDN_UART pin of the TMC

The following schematic is designed for a SAMD21 Xiao board, the GPIO numbers are slightly different for a RP2040 variant:

![](images/schematic-d21.png)

Here is the completed board. This early prototype uses 4 layers to have a ground plane, VCC plane and signals in between:

![](images/routed.png)

The correct pinout for a RP2040 Xiao is:

| **Signal** | **GPIO** |
|------------|----------|
| DIAG       | P07      |
| ENN        | P06      |
| DIR        | P27      |
| STEP       | P28      |
| TX         | P0       |
| RX         | P29      |

Note that P29 is not the [standard RX pin](https://wiki.seeedstudio.com/XIAO-RP2040/) for `Serial1` on the Xiao. This can be changed with `Serial1.setRX(29)` in `init()`.

## Soldering

We soldered the prototypes using stencils + solder paste and reflow, but I had inconsistent communication to the TMC. This might have happened after incorrect settings on the VCC jumpers.

I decided to remove the driver with a hot air gun so I could inspect the solder underneath it:

![](images/solder.jpg)

After aligning a new chip, I manually reflow it with the hot air gun.

![](images/solder_done.jpg)

The final PCB is mounted on the back of a NEMA17 using long M3 screws. Note the VCC jumpers at the bottom.

![](images/pcb.jpg)

## Code

The library [TMCStepper](https://github.com/teemuatlut/TMCStepper) provides a good interface for reading/writing the registers of the TMC. Here's a code snippet for setting up and reading the Stallguard values:

```c++
#include <TMCStepper.h>

#define PIN_DIAG           7 // diagnostic
#define PIN_EN             6 // Enable (inverted)
#define PIN_DIR           27 // direction
#define PIN_STEP          28 // Step
#define PIN_RX            29 // RX
#define PIN_TX             0 // TX
#define SERIAL_PORT Serial1  // Serial1
#define DRIVER_ADDRESS 0b00  // MS1 and MS2 = address
#define STALL_VALUE      50  // [0...255]

#define MICROSTEPS       16

#define R_SENSE 0.1f // 100 mOhm

TMC2209Stepper driver(&SERIAL_PORT, R_SENSE, DRIVER_ADDRESS);


void setup() {
  SERIAL_PORT.setTX(PIN_TX);
  SERIAL_PORT.setRX(PIN_RX);
  SERIAL_PORT.begin(115200);

  pinMode(PIN_DIAG, INPUT);
  pinMode(PIN_EN, OUTPUT);
  pinMode(PIN_STEP, OUTPUT);
  pinMode(PIN_DIR, OUTPUT);

  driver.begin();
  driver.toff(4);
  driver.blank_time(24);
  driver.rms_current(250); // in mA
  driver.microsteps(MICROSTEPS);
  driver.TCOOLTHRS(0xFFFFF); // 20bit max
  driver.semin(5);
  driver.semax(2);
  driver.sedn(0b01);
  driver.SGTHRS(STALL_VALUE); // Stallguard < threshold -> DIAG pin goes up
}

void loop() {
    // make motor turn, needed for valid Stallguard readings
    [...]

    // 9-bit Stallguard reading
    int value = driver.SG_RESULT();
}
```

## Result

![](video/homing.mp4)