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docs: Measuring_Resonances.md improved information on I2C accelerometers and AVR support (#6132) 

More information on I2C accelerometers.

Added in table of MCUs with 400kbit/s I2C support

Signed-off-by: Matthew Swabey <matthew@swabey.org>
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@ -1,35 +1,60 @@
# Measuring Resonances # Measuring Resonances
Klipper has built-in support for ADXL345 accelerometer, which can be used to Klipper has built-in support for the ADXL345 and MPU-9250 compatible
measure resonance frequencies of the printer for different axes, and auto-tune accelerometers which can be used to measure resonance frequencies of the printer
[input shapers](Resonance_Compensation.md) to compensate for resonances. for different axes, and auto-tune [input shapers](Resonance_Compensation.md) to
Note that using ADXL345 requires some soldering and crimping. ADXL345 can be compensate for resonances. Note that using accelerometers requires some
connected to a Raspberry Pi directly, or to an SPI interface of an MCU soldering and crimping. The ADXL345 can be connected to the SPI interface of a
board (it needs to be reasonably fast). Raspberry Pi or MCU board (it needs to be reasonably fast). The MPU family can
be connected to the I2C interface of a Raspberry Pi directly, or to an I2C
interface of an MCU board that supports 400kbit/s *fast mode* in Klipper.
When sourcing ADXL345, be aware that there is a variety of different PCB When sourcing accelerometers, be aware that there are a variety of different PCB
board designs and different clones of them. Make sure that the board supports board designs and different clones of them. If it is going to be connected to a
SPI mode (small number of boards appear to be hard-configured for I2C by 5V printer MCU ensure it has a voltage regulator and level shifters.
pulling SDO to GND), and, if it is going to be connected to a 5V printer MCU,
that it has a voltage regulator and a level shifter.
For ADXL345s, make sure that the board supports SPI mode (a small number of
boards appear to be hard-configured for I2C by pulling SDO to GND).
For MPU-9250/MPU-9255/MPU-6515/MPU-6050/MPU-6500s there are also a variety of
board designs and clones with different I2C pull-up resistors which will need
supplementing.
## MCUs with Klipper I2C *fast-mode* Support
| MCU Family | MCU(s) Tested | MCU(s) with Support |
|:--:|:--|:--|
| Raspberry Pi | 3B+, Pico | 3A, 3A+, 3B, 4 |
| AVR ATmega | ATmega328p | ATmega32u4, ATmega128, ATmega168, ATmega328, ATmega644p, ATmega1280, ATmega1284, ATmega2560 |
| AVR AT90 | - | AT90usb646, AT90usb1286 |
## Installation instructions ## Installation instructions
### Wiring ### Wiring
An ethernet cable with shielded twisted pairs (cat5e or better) is recommended An ethernet cable with shielded twisted pairs (cat5e or better) is recommended
for signal integrity over a long distance. If you still experience signal integrity for signal integrity over a long distance. If you still experience signal
issues (SPI/I2C errors), shorten the cable. integrity issues (SPI/I2C errors):
Connect ethernet cable shielding to the controller board/RPI ground. * Double check the wiring with a digital multimeter for:
* Correct connections when turned off (continuity)
* Correct power and ground voltages
* I2C only:
* Check the SCL and SDA lines' resistances to 3.3V are in the range of 900
ohms to 1.8K
* For full technical details consult [chapter 7 of the I2C-bus specification
and user manual UM10204](https://www.pololu.com/file/0J435/UM10204.pdf)
for *fast-mode*
* Shorten the cable
Connect ethernet cable shielding only to the MCU board/Pi ground.
***Double-check your wiring before powering up to prevent ***Double-check your wiring before powering up to prevent
damaging your MCU/Raspberry Pi or the accelerometer.*** damaging your MCU/Raspberry Pi or the accelerometer.***
#### SPI Accelerometers ### SPI Accelerometers
Suggested twisted pair order: Suggested twisted pair order for three twisted pairs:
``` ```
GND+MISO GND+MISO
@ -37,12 +62,15 @@ GND+MISO
SCLK+CS SCLK+CS
``` ```
##### ADXL345 Note that unlike a cable shield, GND must be connected at both ends.
#### ADXL345
###### Direct to Raspberry Pi ###### Direct to Raspberry Pi
**Note: Many MCUs will work with an ADXL345 in SPI mode(eg Pi Pico), wiring and **Note: Many MCUs will work with an ADXL345 in SPI mode (e.g. Pi Pico), wiring
configuration will vary according to your specific board and available pins.** and configuration will vary according to your specific board and available
pins.**
You need to connect ADXL345 to your Raspberry Pi via SPI. Note that the I2C You need to connect ADXL345 to your Raspberry Pi via SPI. Note that the I2C
connection, which is suggested by ADXL345 documentation, has too low throughput connection, which is suggested by ADXL345 documentation, has too low throughput
@ -86,20 +114,56 @@ Wiring diagrams for some of the ADXL345 boards:
![ADXL345-Pico](img/adxl345-pico.png) ![ADXL345-Pico](img/adxl345-pico.png)
#### I2C Accelerometers ###### Using Raspberry Pi Pico
Suggested twisted pair order: You may connect the ADXL345 to your Raspberry Pi Pico and then connect the
Pico to your Raspberry Pi via USB. This makes it easy to reuse the
accelerometer on other Klipper devices, as you can connect via USB instead
of GPIO. The Pico does not have much processing power, so make sure it is
only running the accelerometer and not performing any other duties.
In order to avoid damage to your RPi make sure to connect the ADXL345 to 3.3V
only. Depending on the board's layout, a level shifter may be present, which
makes 5V dangerous for your RPi.
| ADXL345 pin | Pico pin | Pico pin name |
|:--:|:--:|:--:|
| 3V3 (or VCC) | 36 | 3.3V DC power |
| GND | 38 | Ground |
| CS | 2 | GP1 (SPI0_CSn) |
| SDO | 1 | GP0 (SPI0_RX) |
| SDA | 5 | GP3 (SPI0_TX) |
| SCL | 4 | GP2 (SPI0_SCK) |
Wiring diagrams for some of the ADXL345 boards:
![ADXL345-Pico](img/adxl345-pico.png)
### I2C Accelerometers
Suggested twisted pair order for three pairs (preferred):
```
3.3V+GND
SDA+GND
SCL+GND
```
or for two pairs:
``` ```
3.3V+SDA 3.3V+SDA
GND+SCL GND+SCL
``` ```
##### MPU-9250/MPU-9255/MPU-6515/MPU-6050/MPU-6500 Note that unlike a cable shield, any GND(s) should be connected at both ends.
Alternatives to the ADXL345 are MPU-9250/MPU-9255/MPU-6515/MPU-6050/MPU-6500. #### MPU-9250/MPU-9255/MPU-6515/MPU-6050/MPU-6500
These accelerometers have been tested to work over I2C on the RPi or RP2040(pico)
at 400kbaud. These accelerometers have been tested to work over I2C on the RPi, RP2040 (Pico)
and AVR at 400kbit/s (*fast mode*). Some MPU accelerometer modules include
pull-ups, but some are too large at 10K and must be changed or supplemented by
smaller parallel resistors.
Recommended connection scheme for I2C on the Raspberry Pi: Recommended connection scheme for I2C on the Raspberry Pi:
@ -110,18 +174,34 @@ Recommended connection scheme for I2C on the Raspberry Pi:
| SDA | 03 | GPIO02 (SDA1) | | SDA | 03 | GPIO02 (SDA1) |
| SCL | 05 | GPIO03 (SCL1) | | SCL | 05 | GPIO03 (SCL1) |
![MPU-9250 connected to RPI](img/mpu9250-PI-fritzing.png) The RPi has buit-in 1.8K pull-ups on both SCL and SDA.
Recommended connection scheme for I2C(i2c0a) on the RP2040: ![MPU-9250 connected to Pi](img/mpu9250-PI-fritzing.png)
| MPU-9250 pin | RP2040 pin | RPi pin name | Recommended connection scheme for I2C (i2c0a) on the RP2040:
| MPU-9250 pin | RP2040 pin | RP2040 pin name |
|:--:|:--:|:--:| |:--:|:--:|:--:|
| VCC | 39 | 3v3 | | VCC | 39 | 3v3 |
| GND | 38 | Ground | | GND | 38 | Ground |
| SDA | 01 | GP0 (I2C0 SDA) | | SDA | 01 | GP0 (I2C0 SDA) |
| SCL | 02 | GP1 (I2C0 SCL) | | SCL | 02 | GP1 (I2C0 SCL) |
![MPU-9250 connected to PICO](img/mpu9250-PICO-fritzing.png) The Pico does not include any built-in I2C pull-up resistors.
![MPU-9250 connected to Pico](img/mpu9250-PICO-fritzing.png)
##### Recommended connection scheme for I2C(TWI) on the AVR ATmega328P Arduino Nano:
| MPU-9250 pin | Atmega328P TQFP32 pin | Atmega328P pin name | Arduino Nano pin |
|:--:|:--:|:--:|:--:|
| VCC | 39 | - | - |
| GND | 38 | Ground | GND |
| SDA | 27 | SDA | A4 |
| SCL | 28 | SCL | A5 |
The Arduino Nano does not include any built-in pull-up resistors nor a 3.3V
power pin.
### Mounting the accelerometer ### Mounting the accelerometer
@ -269,14 +349,14 @@ probe_points:
100, 100, 20 # an example 100, 100, 20 # an example
``` ```
#### Configure MPU-6000/9000 series With PICO #### Configure MPU-9520 Compatibles With Pico
PICO I2C is set to 400000 on default. Simply add the following to the Pico I2C is set to 400000 on default. Simply add the following to the
printer.cfg: printer.cfg:
``` ```
[mcu pico] [mcu pico]
serial: /dev/serial/by-id/<your PICO's serial ID> serial: /dev/serial/by-id/<your Pico's serial ID>
[mpu9250] [mpu9250]
i2c_mcu: pico i2c_mcu: pico
@ -291,6 +371,24 @@ probe_points:
pin: pico:gpio23 pin: pico:gpio23
``` ```
#### Configure MPU-9520 Compatibles with AVR
AVR I2C will be set to 400000 by the mpu9250 option. Simply add the following
to the printer.cfg:
```
[mcu nano]
serial: /dev/serial/by-id/<your nano's serial ID>
[mpu9250]
i2c_mcu: nano
[resonance_tester]
accel_chip: mpu9250
probe_points:
100, 100, 20 # an example
```
Restart Klipper via the `RESTART` command. Restart Klipper via the `RESTART` command.
## Measuring the resonances ## Measuring the resonances
@ -319,8 +417,8 @@ problem with ADXL345,
or the faulty sensor. Double-check the power, the wiring (that it matches or the faulty sensor. Double-check the power, the wiring (that it matches
the schematics, no wire is broken or loose, etc.), and soldering quality. the schematics, no wire is broken or loose, etc.), and soldering quality.
**If you are using MPU-6000/9000 series accelerometer and it show up as `mpu-unknown`, use with **If you are using a MPU-9250 compatible accelerometer and it shows up as
caution! They are probably refurbished chips!** `mpu-unknown`, use with caution! They are probably refurbished chips!**
Next, try running `MEASURE_AXES_NOISE` in Octoprint, you should get some Next, try running `MEASURE_AXES_NOISE` in Octoprint, you should get some
baseline numbers for the noise of accelerometer on the axes (should be baseline numbers for the noise of accelerometer on the axes (should be
@ -409,10 +507,11 @@ of the accelerometer between the measurements for X and Y axes: measure the
resonances of X axis with the accelerometer attached to the toolhead and the resonances of X axis with the accelerometer attached to the toolhead and the
resonances of Y axis - to the bed (the usual bed slinger setup). resonances of Y axis - to the bed (the usual bed slinger setup).
However, you can also connect two accelerometers simultaneously, though they However, you can also connect two accelerometers simultaneously, though the
must be connected to different boards (say, to an RPi and printer MCU board), or ADXL345 must be connected to different boards (say, to an RPi and printer MCU
to two different physical SPI interfaces on the same board (rarely available). board), or to two different physical SPI interfaces on the same board (rarely
Then they can be configured in the following manner: available). Then they can be configured in the following manner:
``` ```
[adxl345 hotend] [adxl345 hotend]
# Assuming `hotend` chip is connected to an RPi # Assuming `hotend` chip is connected to an RPi
@ -429,6 +528,30 @@ accel_chip_y: adxl345 bed
probe_points: ... probe_points: ...
``` ```
Two MPUs can share one I2C bus, but they **cannot** measure simultaneously as
the 400kbit/s I2C bus is not fast enough. One must have its AD0 pin pulled-down
to 0V (address 104) and the other its AD0 pin pulled-up to 3.3V (address 105):
```
[mpu9250 hotend]
i2c_mcu: rpi
i2c_bus: i2c.1
i2c_address: 104 # This MPU has pin AD0 pulled low
[mpu9250 bed]
i2c_mcu: rpi
i2c_bus: i2c.1
i2c_address: 105 # This MPU has pin AD0 pulled high
[resonance_tester]
# Assuming the typical setup of the bed slinger printer
accel_chip_x: mpu9250 hotend
accel_chip_y: mpu9250 bed
probe_points: ...
```
[Test with each MPU individually before connecting both to the bus for easy
debugging.]
Then the commands `TEST_RESONANCES AXIS=X` and `TEST_RESONANCES AXIS=Y` Then the commands `TEST_RESONANCES AXIS=X` and `TEST_RESONANCES AXIS=Y`
will use the correct accelerometer for each axis. will use the correct accelerometer for each axis.