Position counter cannot deal with initial negative rotation

Hi everyone

I'm using an optical encoder to keep track of how much my stepper motor has rotated, however I am encountering a problem which I think has a simple solution but I haven't been able to figure it out or find anything online.

My quadrature encoder is connected to a NI 6229-USB DAQ unit and by using the code below, I am able to read data from the encoder.

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s = daq.createSession('ni');

ch = s.addCounterInputChannel ('Dev3', 'ctr0', 'Position');

ch.EncoderType = 'X4'

ch =

Data acquisition counter input position channel 'ctr0' on device 'Dev3':

    EncoderType: X4
   ZResetEnable: 0
    ZResetValue: 0
ZResetCondition: BothHigh
      TerminalA: 'PFI8'
      TerminalB: 'PFI10'
      TerminalZ: 'PFI9'
           Name: ''
             ID: 'ctr0'
         Device: [1x1 daq.ni.DeviceInfo]
MeasurementType: 'Position'

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When I tell my motor to turn in its positive direction (in this case clockwise), the encoder works fine and I get the right angle by using:

 (s.inputSingleScan/(4*1024))*360

where "s.inputSingleScan" gives me the count. The encoder also works if I then tell the motor to in its negative direction, for example if I initialise the session and tell the motor to go to 10degrees and then 5degrees, I get the right value. However, if I initialise the code and I tell the motor to go in the negative direction first, I get nonsensical values i.e. if I tell it to go from 0 to -5 degrees I get an angle of 4x10^6... Any ideas why this is happening?

Answer 1

[Jovan]

Found a previous post with the same problem:

http://www.mathworks.co.uk/matlabcentral/answers/24350-daq-toolbox-counter-input-integer-overflow-problem

The issue is to do with the formatting of the numbers from the DAQ unit, hence they need to be converted. I have found this to work for me:

indx = double(typecast(uint32(s.inputSingleScan),'int32'));

encoder_angle = (indx/4096)*360;