ISO iso 11786 Extreme low speed.

Discussion in 'Precision Farming & GPS' started by strobaal, May 17, 2019 at 2:40 PM.

  1. strobaal

    strobaal New Member


    I am trying to readout the tractor speed with the ISO 11786 port (7 pin connector) in the roof of the tractor with a microcontroller.
    I will get results on the display but only if the tractor drive faster than 1km/h. For my purpose i need to read out the speed from 100 meter/hour and faster. Because we are harvesting cauliflower with this tractor.

    Does someone now of this is possible? Or do I have to find another way to meassure the tractor speed.
  2. Think you’re going to struggle, especially at 100m per hour. Have you put a scope on the output? What micro-controller and how or what are you triggering from, eg edge detect or frequency count?

    Why not use GPS and just use an NMEA feed?
  3. Wombat

    Wombat Member

    East yorks
    At 100m/h they will be into the inaccuracies of GPS positioning
  4. You’d want to be on RTK correction. Then there’s no problem.
  5. strobaal

    strobaal New Member

    I am using an arduino nano to readout the frequency with a frequency measuring libary. According to iso 11786 point 5.2.3 there is nothing told about speed below 1km/h. So maybe it is impossible to do it on this way.
    But there is isobus available on the tractor (Fendt 313 vario s4, and Fendt 724) So now i want to try to read out the 9-pin incab isobus connector with my arduino.
    But first find some information about pinout and that kind of stuff. I hope this is going to work.
    There is no Gps available on the tractor so also that solution is not possible.

    5.2.1 The signal shall be a square wave with a duty cycle between 20 % and 80 %, and with rise and fall times less than 1 ms.
    5.2.2 The signal level of the square wave “mark” (high) shall be greater than 6,3 V and the “space” (low) shall be less than 1,5 V. The output source impedance at “space” (low) shall be 100 7 – 10 7. The load impedance shall be greater than 3 k7.
    5.2.3 At speeds greater than 1 km/h, the speed shall be represented by 130 pulses/m – 5 % (130 Hz/m/s – 5 %) in a standard calibration test.

    Attached Files:

  6. I think from that you can take away that the reading from the 7-pin socket will be unreliable below 1 kph. The only true way to see, is to stick a scope on it and look at the waveform and see how it behaves as you vary the speed down to 0.1 kph.

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