Contents: [Dobrica Pavlinušić's random unstructured stuff]
• Dobrica Pavlinušić's random unstructured stuff (ADXL335) 
• Dobrica Pavlinušić's random unstructured stuff (MPU‑9250) 

This page tries to document my experiments using accelerometers
ADXL335
Board: GY‑61.
ADXL335 3‑axis Accelerometer
 On‑board 3.3V Voltage Regulator
 Analog voltage output centered at 1.65V
 Suitable for connection to 5V and 3.3V systems
Supply Voltage: 3V ‑ 5V
 Full scale range: +/‑3g
 Sensitivity: 300mV/g (Typ)
MPU‑9250
Board: Grove ‑ IMU 10DOF v1.1
https://wiki.seeedstudio.com/Grove‑IMU_10DOF/ 
Grove ‑ IMU 10DOF v1.1.pdf 

MPU‑9250 addr: 0x68
 BMP180 addr: 0x77
This board has 5V ‑> 3V3 level shifter but works with 3V3 as VCC
root@rpi4:~# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- 77

root@rpi4:~# modprobe configs
root@rpi4:~# zgrep INV /proc/config.gz
CONFIG_INV_MPU6050_IIO=m
CONFIG_INV_MPU6050_I2C=m
# CONFIG_INV_MPU6050_SPI is not set

root@rpi4:~# modprobe inv-mpu6050-i2c

root@rpi4:~# echo mpu9250 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
[Sat Jan  9 14:10:25 2021] inv-mpu6050-i2c 1-0068: mounting matrix not found: using identity...
[Sat Jan  9 14:10:25 2021] inv-mpu6050-i2c 1-0068: 1-0068 supply vddio not found, using dummy regulator
[Sat Jan  9 14:10:25 2021] inv-mpu6050-i2c 1-0068: trigger probe fail -22
[Sat Jan  9 14:10:25 2021] inv-mpu6050-i2c: probe of 1-0068 failed with error -22
[Sat Jan  9 14:10:25 2021] i2c i2c-1: new_device: Instantiated device mpu9250 at 0x68

root@rpi4:~# echo bmp180 0x77 > /sys/class/i2c-adapter/i2c-1/new_device
[Sat Jan  9 14:12:17 2021] i2c i2c-1: new_device: Instantiated device bmp180 at 0x77
[Sat Jan  9 14:12:17 2021] bmp280 1-0077: 1-0077 supply vddd not found, using dummy regulator
[Sat Jan  9 14:12:17 2021] bmp280 1-0077: 1-0077 supply vdda not found, using dummy regulator
[Sat Jan  9 14:12:17 2021] bmp280 1-0077: non-rising trigger given for EOC interrupt, trying to enforce it
[Sat Jan  9 14:12:17 2021] bmp280 1-0077: unable to request DRDY IRQ

root@rpi4:~# iio_info
Library version: 0.16 (git tag: v0.16)
Compiled with backends: local xml ip usb serial
IIO context created with local backend.
Backend version: 0.16 (git tag: v0.16)
Backend description string: Linux rpi4 5.4.79-v7l+ #1373 SMP Mon Nov 23 13:27:40 GMT 2020 armv7l
IIO context has 1 attributes:
        local,kernel: 5.4.79-v7l+
IIO context has 1 devices:
        iio:device0: bmp180
                2 channels found:
                        pressure:  (input)
                        3 channel-specific attributes found:
                                attr  0: input value: 100.646000000
                                attr  1: oversampling_ratio value: 8
                                attr  2: oversampling_ratio_available value: 1 2 4 8
                        temp:  (input)
                        3 channel-specific attributes found:
                                attr  0: input value: 24800
                                attr  1: oversampling_ratio value: 1
                                attr  2: oversampling_ratio_available value: 1

Hm. bmp180 works, mpu9250 doesn't
It needs full device tree overlay https://github.com/dpavlin/linux‑gpio‑pinout/blob/master/device‑tree/grove‑imu10dof.dts