5 replies to this topic

[Sinan]

Hi everyone,

I am trying to build a variometer using the Mod-1009 board for MS5611-01BA barometric pressure sensor from Embedded Adventures.

Unfortunately, I cannot read values from the i2c port. SDA is connected to Analog 4, SCLK to 5 and the VCC to 3.3v. I am using the latest framework (4.2).

I am OK with C# and .net but I am clueless in this world. Bellow is my code where the device.Execute always returns zero in the ReadFromDevice method.

using System;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;

namespace MS5611baro
{
  // Mod-1009 board for MS5611-01BA Barometric Pressure Sensor from
  // Embedded Adventures (http://www.embeddedadventures.com/barometric_pressure_sensor_module_mod-1009.html) 
  // MS5611 datasheet http://www.embeddedadventures.com/datasheets/ms5611.pdf
  // Mod-1009 description http://www.embeddedadventures.com/datasheets/MOD-1009_hw_v1.pdf
  // 
  // VCC  --> 3.3v
  // SDA  --> Analog 4
  // SCLK --> Analog 5
  // 
  // Pull up resistors: (from Mod-1009 description) The board comes with the pull-up resistors enabled. If you are
  //   connecting to an existing I2C buss that already has pull-up resistors, or you are using internal pull-ups in 
  //   your microcontroller, you can disable the pull-up resistors by cutting the PCB jumpers on the MOD-1009 board. 
  public class MS5611_MOD1009
  {
    private const byte _cmdReset = 0x1E;
    private const byte _cmdPromReadBase = 0xa0;
   
    private const ushort _i2cAddr = 0x76; //Embedded Adventures module CSB is VCC --> HIGH --> 0x76

    public UInt16[] CalibrationArray = new UInt16[6];
    public int LastTransactionCount = -1;

    private I2CDevice _device = new I2CDevice(new I2CDevice.Configuration(_i2cAddr, 10));

    /// <summary> Mod-1009 board for MS5611-01BA Barometric Pressure Sensor from Embedded Adventures</summary>
    public MS5611_MOD1009()
    {
      while (LastTransactionCount < 1)
      {
        WriteToDevice(_cmdReset, 100); // ResetSensor();       
      }
    }

    public bool WriteToDevice(byte command, int timeOut = 5)
    {
      I2CDevice.I2CWriteTransaction wt = I2CDevice.CreateWriteTransaction(new byte[] { command });
      LastTransactionCount = this._device.Execute(new I2CDevice.I2CTransaction[] { wt }, 3);
      return LastTransactionCount > 0;
    }

    public bool ReadFromDevice(byte[] readBuf, int timeOut = 100)
    {
      var rtArr = new I2CDevice.I2CReadTransaction[] { I2CDevice.CreateReadTransaction(readBuf) };
      LastTransactionCount = _device.Execute(rtArr, timeOut);  // --> returns allways zero
      return LastTransactionCount == readBuf.Length;
    }

    public void ReadCalibrationData()
    {
      for (byte i = 0; i < 6; i++)
      {
        CalibrationArray[i] = ReadSingleCalibrationValue((byte)(i + 1));
      }
    }

    private UInt16 ReadSingleCalibrationValue(byte valueToRead)
    {
      //  1 0 1 0 X X X 0  - The XXX part is used for the parameter index
      byte paramIndex = (byte)(_cmdPromReadBase + (valueToRead << 1));
      // This sets up the system into PROM read mode.
      if (WriteToDevice(paramIndex))       // --> returns true
      {
        byte[] readBuf = new byte[2];
        // This part gets the data from the system.
        if (ReadFromDevice(readBuf, 100)) // --> returns allways false, readBuf is empty {0, 0}
        {
          return (UInt16)(readBuf[0] << 8 | readBuf[1]);
        }
      }
      return 0;
    }
  }
}

using System;
using System.Threading;
using Microsoft.SPOT;

namespace MS5611baro
{
  public class Program
  {
    public static void Main()
    {
      var baro = new MS5611_MOD1009();
      baro.ReadCalibrationData();
    }
  }
}

Thanks for help,
Sinan

[Sinan]

Just discovered the I2CAdapter class by Guido (gbreder). It looks promissing.

Regards,
Sinan

[Sinan]

Hi,

I have completely refactored my code around the I2CAdapter class. Although the code looks much better now, it still doesn't work. All read actions return 0 bytes.

using System;
using System.Threading;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;
using Netduino.Extender.TransferAdapters;  

namespace MS5611baro
{
  public class Program
  {
    private const ushort _i2cAddr =0x76; //  Embedded Adventures module CSB is VCC --> HIGH --> 0x76
    static I2CDevice.Configuration _config;
    // From: Guido (gbreder)
    // http://forums.netduino.com/index.php?/topic/3471-netduino-firmware-v420-rc4-netduino-netduino-plus/page__hl__createreadtransaction__st__80
    static I2CAdapter _adapter;

    public static void Main()
    {
      _config = new I2CDevice.Configuration(_i2cAddr, 10);
      _adapter = I2CAdapter.Instance;
      ResetMS5611();
      UInt16[] calibrationArray = ReadCalibrationParameters();
      while (true)
      {
        int tempRaw = ReadIntFrom24bit(0x58);     // Command to convert temp D2 (OSR=4096)
        int pressureRaw = ReadIntFrom24bit(0x48); // Command to convert pressure D1 (OSR=4096)
      }
    }

    private static int ReadBytes(byte[] buf)
    {
      return _adapter.ReadBytes(_config, buf);
      // return _adapter.ReadInternalAddressBytes(_config, buf, _i2cAddr, 1);
    }

    static int WriteByte(byte B)
    {
      return _adapter.WriteBytes(_config, new byte[] { b });
      // return _adapter.WriteInternalAddressBytes(_config, new byte[] { b }, _i2cAddr, 1);
    }

    private static void ResetMS5611()
    {
      WriteByte(0x1E); // Reset command
      Thread.Sleep(100);
    }

    private static UInt16[] ReadCalibrationParameters()
    {
      UInt16[] calibrationArray = new UInt16[6];
      byte[] readBuf = new byte[2];
      for (int i = 0; i < 6; i++)
      {
        byte paramIndex = (byte)(0xA0 + ((i + 1) << 1)); // 1010XXX0 - The XXX part for the parameter index        
        WriteByte(paramIndex);                           // This sets up the system into PROM read mode.
        ReadBytes(readBuf);
        calibrationArray[i] = (UInt16)(readBuf[0] << 8 | readBuf[1]);
      }
      return calibrationArray;
    }

    private static int ReadIntFrom24bit(byte command)
    {
      WriteByte(command); 
      Thread.Sleep(10);
      WriteByte(0);  // Send read ADC command
      byte[] buf24 = new byte[3];
      ReadBytes(buf24);
      int result = (buf24[0] * 65536) + (buf24[1] * 256) + buf24[2];
      return result;
    }
  }
}

I have double checked all connections and read lots of documentation. I don’t know where to go from here.

Kind regards, Sinan

[Sinan]

Problem solved by applying 1.8K pull-up resistors. I first replaced the built in 10K resistors by 2.2K resistors but it didn’t worked. Also experimented with couple of other resistors without any luck. At the end, I have used the 10K and the 2.2K resistors in parallel (=1.8K) and finally tada… Cheers, Sinan

[Sinan]

I keep replying my own post, but one more update…

After reading this article and some more experiments, I have discovered that most trouble is caused by the type and/or the length of the cables on my breadboard. The SDA/CLK cables where 20cm long and I don’t know how thick they were. The connections where all OK. Anyway, everything started to work flawlessly after replacing these cables with very short (2 cm) ones. The pull-up resistor values are also less critical now, I can use the device with various resistors from 1k to 10k.
I suppose that this problem is caused due to wrong capacitance of the signal bus. Learning a lot these days.

Cheers, Sinan

[Coder Myers]

Thanks for this post, I believe I'm having the same issue with various other sensors.