I'm making an ultra-low powered arduino vibration sensor. My sensor is the MPU6050 on a GY521 breakout board.
I've managed to get the MPU6050 into it's lowest power mode which is waking every 1.25Hz and reading the accel only. According to the datasheet this should be 10µA.
However when the arduino is reading data from the MPU, it draws 1.74mA! And even when it is not reading data it is drawing 0.14mA!
Does anyone know why it draws more power when the I2C bus is active?
My sketch is below. You can see how the arduino sleeps for 8 seconds every 7 seconds. During the sleep, the current consumption of the MPU is 0.14mA, and when not in sleep it is 1.74mA.
My current meter is between the MPU VCC pin and the 3.3V Pro mini pin.
This is the serial monitor output showing that the MPU is on low current mode:
Enter AT commands:
Initializing I2C devices...
Testing device connections...
MPU6050 connection successful
3a/g: -756 -68 15100 0 0 0
a/g: -804 -76 15012 0 0 0
a/g: -680 -32 15100 0 0 0
sleeping now
a/g: -780 -44 15024 0 0 0
a/g: -712 32 15248 0 0 0
a/g: -756 -28 15092 0 0 0
a/g: -796 -60 15032 0 0 0
sleeping now
// I2C device class (I2Cdev) demonstration Arduino sketch for MPU6050 class
// 10/7/2011 by Jeff Rowberg <jeff@rowberg.net>
// Updates should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
//
// Changelog:
// 2013-05-08 - added multiple output formats
// - added seamless Fastwire support
// 2011-10-07 - initial release
// I2Cdev and MPU6050 must be installed as libraries, or else the .cpp/.h files
// for both classes must be in the include path of your project
#include "I2Cdev.h"
#include "MPU6050.h"
#include "LowPower.h"
#include <SoftwareSerial.h>
SoftwareSerial BTSerial(12, 11); // RX | TX
// Arduino Wire library is required if I2Cdev I2CDEV_ARDUINO_WIRE implementation
// is used in I2Cdev.h
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
#include "Wire.h"
#endif
// class default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for InvenSense evaluation board)
// AD0 high = 0x69
MPU6050 accelgyro;
//MPU6050 accelgyro(0x69); // <-- use for AD0 high
int16_t ax, ay, az;
int16_t gx, gy, gz;
long sendcurrmillis;
long sendprevmillis;
int sendinterval = 7000;
long dispcurrmillis;
long dispprevmillis;
int dispinterval = 2000;
uint8_t WakeFreq;
// uncomment "OUTPUT_READABLE_ACCELGYRO" if you want to see a tab-separated
// list of the accel X/Y/Z and then gyro X/Y/Z values in decimal. Easy to read,
// not so easy to parse, and slow(er) over UART.
#define OUTPUT_READABLE_ACCELGYRO
// uncomment "OUTPUT_BINARY_ACCELGYRO" to send all 6 axes of data as 16-bit
// binary, one right after the other. This is very fast (as fast as possible
// without compression or data loss), and easy to parse, but impossible to read
// for a human.
//#define OUTPUT_BINARY_ACCELGYRO
#define LED_PIN 13
bool blinkState = false;
void setup() {
// join I2C bus (I2Cdev library doesn't do this automatically)
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
Wire.begin();
#elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
Fastwire::setup(400, true);
#endif
// initialize serial communication
// (38400 chosen because it works as well at 8MHz as it does at 16MHz, but
// it's really up to you depending on your project)
Serial.begin(9600);
Serial.println("Enter AT commands:");
BTSerial.begin(9600); // HC-05 default speed
// initialize device
Serial.println("Initializing I2C devices...");
accelgyro.initialize();
// verify connection
Serial.println("Testing device connections...");
Serial.println(accelgyro.testConnection() ? "MPU6050 connection successful" : "MPU6050 connection failed");
// use the code below to change accel/gyro offset values
/*
Serial.println("Updating internal sensor offsets...");
// -76 -2359 1688 0 0 0
Serial.print(accelgyro.getXAccelOffset()); Serial.print("\t"); // -76
Serial.print(accelgyro.getYAccelOffset()); Serial.print("\t"); // -2359
Serial.print(accelgyro.getZAccelOffset()); Serial.print("\t"); // 1688
Serial.print(accelgyro.getXGyroOffset()); Serial.print("\t"); // 0
Serial.print(accelgyro.getYGyroOffset()); Serial.print("\t"); // 0
Serial.print(accelgyro.getZGyroOffset()); Serial.print("\t"); // 0
Serial.print("\n");
accelgyro.setXGyroOffset(220);
accelgyro.setYGyroOffset(76);
accelgyro.setZGyroOffset(-85);
Serial.print(accelgyro.getXAccelOffset()); Serial.print("\t"); // -76
Serial.print(accelgyro.getYAccelOffset()); Serial.print("\t"); // -2359
Serial.print(accelgyro.getZAccelOffset()); Serial.print("\t"); // 1688
Serial.print(accelgyro.getXGyroOffset()); Serial.print("\t"); // 0
Serial.print(accelgyro.getYGyroOffset()); Serial.print("\t"); // 0
Serial.print(accelgyro.getZGyroOffset()); Serial.print("\t"); // 0
Serial.print("\n");
*/
// configure Arduino LED for
pinMode(LED_PIN, OUTPUT);
accelgyro.setWakeFrequency(3); //this sets the wakeup frequency of the accel. 0 = 1.25 HZ, 1 = 2.5hz, 2 = 5hz, 3 = 10hz
accelgyro.setWakeCycleEnabled(1); //this puts the mpu6050 into the wake cycle mode, where it sleeps, and then wakes, reads accel (maybe more) and puts in i2c buffer to be read.
WakeFreq = accelgyro.getWakeFrequency(); //this returns the wakeup frequency that the accel is set to. 0 = 12
Serial.print(WakeFreq);
BTSerial.write("AT+SLEEP");
}
void loop() {
// read raw accel/gyro measurements from device
accelgyro.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);
sendcurrmillis = millis();
if(sendcurrmillis - sendprevmillis > sendinterval)
{
entersleep();
sendprevmillis = millis();
}
dispcurrmillis = millis();
if(dispcurrmillis - dispprevmillis > dispinterval)
{
Serial.print("a/g:\t");
Serial.print(ax); Serial.print("\t");
Serial.print(ay); Serial.print("\t");
Serial.print(az); Serial.print("\t");
Serial.print(gx); Serial.print("\t");
Serial.print(gy); Serial.print("\t");
Serial.println(gz);
dispprevmillis = millis();
}
// these methods (and a few others) are also available
//accelgyro.getAcceleration(&ax, &ay, &az);
//accelgyro.getRotation(&gx, &gy, &gz);
}
void entersleep() {
Serial.println("sleeping now");
Serial.flush();
LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
//delay(2000);
}
void BTthroughput()
{
// Keep reading from HC-05 and send to Arduino Serial Monitor
if (BTSerial.available())
Serial.write(BTSerial.read());
// Keep reading from Arduino Serial Monitor and send to HC-05
if (Serial.available())
BTSerial.write(Serial.read());
}
void BTsendrecv()
{
// Keep reading from HC-05 and send to Arduino Serial Monitor
if (BTSerial.available())
Serial.write(BTSerial.read());
// Keep reading from Arduino Serial Monitor and send to HC-05
if (Serial.available())
BTSerial.write(Serial.read());
}
Why is the I2C data transfer using so much power? Does anyone know?
Here's my wiring diagram: