esp8266mpu9250toOSC

This repository contains code for sending data from an accelerometer sensor with a microcontroller to another device using OSC.

The microcontroller code is using the Arduino environment (see https://github.com/esp8266/Arduino). The receiving examples located in sc/ are written in SuperCollider.

Hardware

• Espressif ESP8266 microcontroller (e.g. Adafruit HUZZAH)
• InvenSense MPU-9250 (e.g. GY-9250 board)
• LiPo battery
• power switch
• (optionally) a pair of resistors to make a voltage divider for measuring battery voltage (maximum voltage of ESP8266's ADC is 1V)

MPU-9250 should be connected to the board using an I2C interface. Most pins can be used for this purpose (refer to ESP8266's documentation). Additionally, there should be one more connection to 9250's interrupt pin (this can be any pin except 16 and probably 0).

MPU-9250 can be powered directly from the battery, or from the HUZZAH's 3.3V regulator.

For programming and setting the microcontroller, one needs to use a serial interface (e.g. USB-serial)

Voltage measurement

In order to measure voltage with the HUZZAH board, it's necessary to create a voltage divider with two resistors, connecting VBat+ to the ADC input, e.g.

VBat+     GND
  \       /
1000kΩ  100kΩ
    \   /
     ADC

The values can be different, the point is that they need to bring the battery voltage (e.g. LiPo Battery might have around 4.2V when full) under the 1V max.

If the value of the resistors is different than here, it should be modified in the code (see below).

Firmware

Pin configuration

Pins for the I2C are set when initializing the Wire library, where you can adapt them as needed.

// initialize accelerometer device
Serial.println("Initializing I2C devices");
Wire.setClock(400000);//speed up I2C
Wire.begin(4, 2); //define which pins are used for I2C: Wire.begin(int sda, int scl)

Interrupt pin is set as a variable:

// Pin definitions
int intPin = 5;

Battery voltage

If necessary, resistor values for the voltage divider should be updated in the code:

//voltage measurement
float r1 = 100; //lower resistor value (kOhm)
float r2 = 1000; //higher resistor value (kOhm)

Flashing

Programing the microcontroller should be straightforward:

• Download board definition and required library (OSC) in Arduino
• Open the esp8266mpu9250kwiner.ino file
• Select the appropriate board and serial port
• Compile and upload
  • note that Adafruit HUZZAH needs to be put manually into the firmward upload mode by holding GPIO0 button down while powering on/resetting the board

Setup

After flashing the firmware, some settings need to be set in order for the system to be operational. Interaction with the microcontroller is facilitated through a serial connection at the baud rate of 115200 using ASCII characters.

Parameters that need to be set before using the microcontroller

• sensor name
• WiFi SSID
• WiFi password (if used)
• accelerometer and gyroscope calibration
• magnetometer calibration
• destination IP and port (this can also be set by sending an OSC message to the microcontroller, see SuperCollider example below)

Commands

In order to read the current value of a parameter, send <parameterName> <enter>. To set the parameter, send <parameterName> <values> <enter>.

This is the list of available commands:

command	values	description
?		print available commands (short)
??		print available commands with descritpions
name	<string>	name of the sensor (will also set the OSC path)
ssid	<string>	WiFi network name
pwd	<string>	WiFi network password (if used); set to "" to disable
calibrateAccGyro		start calibration process for Accelerometer and Gyro; also see below (*)
calibrateMag		start calibration process for Accelerometer and Gyro; also see below (*)
ip	e.g. 192.168.1.10	destination IP
port	e.g. 10000	destination port
myIP		get microcontroller's IP
myPort		get microcontroller's receiving port
format	space-delimited list of strings	message format; see formatInfo
formatInfo		list available format names
version		print version string
oscPath		print osc path
fallback	0 or 1	send sensor data over the serial port
status		get information on the current status

(*) NOTE: currently the microcontroller needs to be connected to the WiFi network in order for the callibration to work

Calibration

Make sure to be connected to the WiFi network first.

Accelerometer and Gyro calibration

Type calibrateAccGyro.

The accelerometer should be stable and perfectly flat.

Magnetometer calibration

Type calibrateMag.

The sensor should be rotated along all axis for about 15 seconds. Make sure to not be too close to strong magnetic fields.

Setting send format

OSC messages are sent with the path /acc/<accelerometerName>, followed by the defined sensor data.

Available data:

data	description
acc	accelerometer data (x, y, z), in G (gravity force)
gyro	gyroscope data (x, y, z)
accgyro	shorthand for accelerometer and gyroscope data (x, y, z, x, y, z)
yawpitchroll	yaw, pitch, roll
quaternion	quaternion data (w, x, y, z)
counter	counter from 0-255, increments with each message and wraps around, e.g. for detecting lost packets
b1, b2, b3,b4	button 1-4 data (value 0 or 1, send continuously)
realaccel	linear acceleration (untested)

To set the format, type format <name1> <name2> <name3> etc, e.g. format acc or format acc yawpitchroll.

Receiving data in SuperCollider

See sc/ folder for SuperCollider code.

sensor management.scd allows for setting all the devices on the network to send messages to SuperCollider.

orientation visualization.scd provides a simple visualization for the yawpitchroll data (use format acc yawpitchroll).

accelerometer and granulator.scd is a simple live sound example that uses accelerometer data.