EVolocity 3 Axis G-Meter

A telemetry system could be used to monitor the progress of your electric vehicle and provide feedback to the team & driver about how efficiently/fast it is being driven. As part of a telemetry system lateral, longitudinal, and vertical acceleration could be monitored using a cheap ADXL345 mems accelerometer

Netduino based 3D GMeter

Netduino based 3D G-Meter

Bill of Materials for my engineering proof of concept (Prices as at May 2015)

The sample code reads the acceleration data from the ADXL345 using a driver originally created by Love Electronics. It then displays the magnitude of the scaled acceleration on 3 x LED Bars using code written by Famoury Toure

OutputPort Xcin = new OutputPort(Pins.GPIO_PIN_D0, false);
OutputPort Xdin = new OutputPort(Pins.GPIO_PIN_D1, false);
OutputPort Ycin = new OutputPort(Pins.GPIO_PIN_D3, false);
OutputPort Ydin = new OutputPort(Pins.GPIO_PIN_D4, false);
OutputPort Zcin = new OutputPort(Pins.GPIO_PIN_D5, false);
OutputPort Zdin = new OutputPort(Pins.GPIO_PIN_D6, false);

GroveLedBarGraph Xbar = new GroveLedBarGraph(Xcin, Xdin);
GroveLedBarGraph Ybar = new GroveLedBarGraph(Ycin, Ydin);
GroveLedBarGraph Zbar = new GroveLedBarGraph(Zcin, Zdin);

using (OutputPort i2cPort = new OutputPort(Pins.GPIO_PIN_SDA, true))
{
   i2cPort.Write(false);
}

ADXL345 accel = new ADXL345(0x53);
accel.EnsureConnected();
accel.Range = 2;
accel.FullResolution = true;
accel.EnableMeasurements();
accel.SetDataRate(0x0F);

while (true)
{
   accel.ReadAllAxis();

   uint xValue = (uint)(((accel.ScaledXAxisG / 1.0 ) + 1.0) * 5.0) ;
   uint xbar = 1;
   xbar = xbar << (int)xValue;
   Xbar.setLED(xbar);

   uint yValue = (uint)(((accel.ScaledYAxisG / 1.0) + 1.0) * 5.0);
   uint ybar = 1;
   ybar = ybar << (int)yValue;
   Ybar.setLED(ybar);

   uint zValue = (uint)((-(accel.ScaledZAxisG / 1.0) + 2.0) * 5.0);
   uint zbar = 1;
   zbar = zbar << (int)zValue;
   Zbar.setLED(zbar);

   Thread.Sleep(20);
   }
}

EV Telemetry Demo

At EV Camp in June 2014 I talked about real-time telemetry for the electric carts. This is a demo of how this could be done using a couple of Netduinos, nRF24L01 modules and some other hardware

Telemetry Demo

Accelerometer and Throttle Position Telemetry

Bill of materials (Prices as at July 2014)

  • 2 x Netduino Plus 2 USD60,NZD108 or Netduino 2 USD33,NZD60
  • 2 x Embedded Coolness nRF24L01shields V1.1b + high power modules AUD17.85
  • 2 x Grove Base Shields V2 USD8.90
  • 1 x Grove ADX345 Accelerometer USD9.90
  • 1 x Grove Rotary Angle Sensor USD2.90
  • 1 x Grove 16×2 LCD USD13.90 (Using earlier serial display in pictures)

The mobile device configures the Gralin nRF24L01 library, initialises the Love Electronics ADXL345 Accelerometer library, and creates two timers, one for the throttle position the other for the accelerometer.

_module.OnTransmitFailed += OnSendFailure;
_module.OnTransmitSuccess += OnSendSuccess;
_module.Initialize(SPI.SPI_module.SPI1, Pins.GPIO_PIN_D7, Pins.GPIO_PIN_D3, Pins.GPIO_PIN_D2);
_module.Configure(myAddress, channel);
_module.Enable();

accel.EnsureConnected();
accel.Range = 2;
accel.FullResolution = true;
accel.EnableMeasurements();
accel.SetDataRate(0x0F);

Timer throttlePositionUpdates = new Timer(throttleTimerProc, null, 500, 500);
Timer accelerometerUpdates = new Timer(AccelerometerTimerProc, null, 500, 500);

Thread.Sleep( Timeout.Infinite ) ;

The Accelerometer timer reads the x, y & z accelerations then sends the data as an ASCII string (rather than Unicode) to save space (maximum message length is 32 bytes)

private void AccelerometerTimerProc(object state)
{
accel.ReadAllAxis();
Debug.Print("A- X = " + accel.ScaledXAxisG.ToString("F2") + " Y = " + accel.ScaledYAxisG.ToString("F2") + " Z = " + accel.ScaledZAxisG.ToString("F2"));

_module.SendTo(baseStationAddress, Encoding.UTF8.GetBytes("A " + accel.ScaledXAxisG.ToString("F1") + " " + accel.ScaledYAxisG.ToString("F1") + " " + accel.ScaledZAxisG.ToString("F1")));
}

The base station works in a similar way, configuring the nRF24L01 library then displaying the received messages on the LCD Display.

MPU 6050 Quadcopter IMU has arrived

The  3 x MPU 6050 breakout boards (GY521) I ordered on Alibaba arrived from China yesterday. I’m looking at using a device which has both an accelerometer & gyroscope in one package rather than an IMU assembled from several discrete devices to make the software simpler (only one I2C bus address).

To make the Microsoft I2C implementation work with multiple discrete devices usually requires a layer of abstraction like commonly used AbstractI2CDevice class which I was wanting to avoid in this project.

The test rig for my light weight high performance driver, a netduino 2 plus & breakout board.

Image

If I need a compass to make the Quadcopter controller work I’ll upgrade to an MPU 9150.

I2C read rates on Netduino Plus vs Netduino plus 2

As part of my quadcopter project I purchased a Netduino Plus 2 for the flight controller. The increased performance 48MHz vs. 168MHz CPU and other improvements looked like it could make it possible to implement most or all of the control algorithms in C#.

So I could compare the performance of the I2C interfaces I setup two test rigs which polled an ADXL345 Accelerometer (using the Love Electronics sample code) 10,000 times for X,Y & Z acceleration values.

NetduinoPlusAccelerometer

The different I2C pins on the Netduino plus 2 required some jumper cables

Netduino2PlusAccelerometer

Both devices were running NetMF 4.2 and I monitored the output of the test harness using MF Deploy.

Netduino Plus

22.2797,22.3126,22.3313,22.3129,22.3590,22.3689,22.3497,22.3049,22.3649,22.3836

Average 22.3 seconds roughly 450/sec

Netduino Plus 2

6.8312,6.8059,6.8003,6.8051,6.8319,6.7999,6.8104,6.8194,6.8233,6.8096

Average 6.8 seconds roughly 1470/sec