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