From 27dab0ee517a6ab8197faa19e12c2911f67b712c Mon Sep 17 00:00:00 2001
From: "Dr. Matthew Swabey" <matthew@swabey.org>
Date: Fri, 7 Apr 2023 11:45:54 -0400
Subject: [PATCH] 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>
---
docs/Measuring_Resonances.md | 199 ++++++++++++++++++++++++++++-------
1 file changed, 161 insertions(+), 38 deletions(-)
diff --git a/docs/Measuring_Resonances.md b/docs/Measuring_Resonances.md
index d09c30543..91d538a4e 100644
--- a/docs/Measuring_Resonances.md
+++ b/docs/Measuring_Resonances.md
@@ -1,35 +1,60 @@
# Measuring Resonances
-Klipper has built-in support for ADXL345 accelerometer, which can be used to
-measure resonance frequencies of the printer for different axes, and auto-tune
-[input shapers](Resonance_Compensation.md) to compensate for resonances.
-Note that using ADXL345 requires some soldering and crimping. ADXL345 can be
-connected to a Raspberry Pi directly, or to an SPI interface of an MCU
-board (it needs to be reasonably fast).
+Klipper has built-in support for the ADXL345 and MPU-9250 compatible
+accelerometers which can be used to measure resonance frequencies of the printer
+for different axes, and auto-tune [input shapers](Resonance_Compensation.md) to
+compensate for resonances. Note that using accelerometers requires some
+soldering and crimping. The ADXL345 can be connected to the SPI interface of a
+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
-board designs and different clones of them. Make sure that the board supports
-SPI mode (small number of boards appear to be hard-configured for I2C by
-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.
+When sourcing accelerometers, be aware that there are a variety of different PCB
+board designs and different clones of them. If it is going to be connected to a
+5V printer MCU ensure it has a voltage regulator and level shifters.
+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
### Wiring
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
-issues (SPI/I2C errors), shorten the cable.
+for signal integrity over a long distance. If you still experience signal
+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
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
@@ -37,12 +62,15 @@ GND+MISO
SCLK+CS
```
-##### ADXL345
+Note that unlike a cable shield, GND must be connected at both ends.
+
+#### ADXL345
###### Direct to Raspberry Pi
-**Note: Many MCUs will work with an ADXL345 in SPI mode(eg Pi Pico), wiring and
-configuration will vary according to your specific board and available pins.**
+**Note: Many MCUs will work with an ADXL345 in SPI mode (e.g. Pi Pico), wiring
+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
connection, which is suggested by ADXL345 documentation, has too low throughput
@@ -86,20 +114,56 @@ Wiring diagrams for some of the ADXL345 boards:
-#### 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:
+
+
+
+### I2C Accelerometers
+
+Suggested twisted pair order for three pairs (preferred):
+
+```
+3.3V+GND
+SDA+GND
+SCL+GND
+```
+
+or for two pairs:
```
3.3V+SDA
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.
-These accelerometers have been tested to work over I2C on the RPi or RP2040(pico)
-at 400kbaud.
+#### MPU-9250/MPU-9255/MPU-6515/MPU-6050/MPU-6500
+
+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:
@@ -110,18 +174,34 @@ Recommended connection scheme for I2C on the Raspberry Pi:
| SDA | 03 | GPIO02 (SDA1) |
| SCL | 05 | GPIO03 (SCL1) |
-
+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 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 |
| GND | 38 | Ground |
| SDA | 01 | GP0 (I2C0 SDA) |
| SCL | 02 | GP1 (I2C0 SCL) |
-
+The Pico does not include any built-in I2C pull-up resistors.
+
+
+
+##### 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
@@ -269,14 +349,14 @@ probe_points:
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:
```
[mcu pico]
-serial: /dev/serial/by-id/<your PICO's serial ID>
+serial: /dev/serial/by-id/<your Pico's serial ID>
[mpu9250]
i2c_mcu: pico
@@ -291,6 +371,24 @@ probe_points:
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.
## Measuring the resonances
@@ -319,8 +417,8 @@ problem with ADXL345,
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.
-**If you are using MPU-6000/9000 series accelerometer and it show up as `mpu-unknown`, use with
-caution! They are probably refurbished chips!**
+**If you are using a MPU-9250 compatible accelerometer and it shows up as
+`mpu-unknown`, use with caution! They are probably refurbished chips!**
Next, try running `MEASURE_AXES_NOISE` in Octoprint, you should get some
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 Y axis - to the bed (the usual bed slinger setup).
-However, you can also connect two accelerometers simultaneously, though they
-must be connected to different boards (say, to an RPi and printer MCU board), or
-to two different physical SPI interfaces on the same board (rarely available).
-Then they can be configured in the following manner:
+However, you can also connect two accelerometers simultaneously, though the
+ADXL345 must be connected to different boards (say, to an RPi and printer MCU
+board), or to two different physical SPI interfaces on the same board (rarely
+available). Then they can be configured in the following manner:
+
```
[adxl345 hotend]
# Assuming `hotend` chip is connected to an RPi
@@ -429,6 +528,30 @@ accel_chip_y: adxl345 bed
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`
will use the correct accelerometer for each axis.