ISO iso 11786 Extreme low speed.

[strobaal]

Hello,

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.

 

[Pheasant Surprise]

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?

 

[Wombat]

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?

At 100m/h they will be into the inaccuracies of GPS positioning

 

[Pheasant Surprise]

At 100m/h they will be into the inaccuracies of GPS positioning

You’d want to be on RTK correction. Then there’s no problem.

 

[strobaal]

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?

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.

 

[Pheasant Surprise]

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.

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.