Get feed rate from AGO and transform it into weedkiller sprayer computer compatible pulses

Hi, I need help getting the ground speed from AGOPENGPS and transforming it into pulses similar to those produced by the wheel sensor that many sprinklers incorporate. These sensors produce pulses at the same time that it detects the teeth of a pinion or perforated circular ring.

That is more difficult than it seams. Yes, there is a precise GNSS signal, but it comes with a delay. Out of this, you would have to extract the speed (Pythagoras is your friend…) and feed it into a PLL circuit in either hard- or software generating the signal. Possible for sure, but simple and not so interesting for a lot of people, because modern tracktors all provide this signal.

I was going to make a post about this also!

Currently the only reason I still have a Deere SF3000 on my tractor, is for its speed output for my sprayer rate controller, one pin on the starfire receivers is an emulated radar output (some tractors have the radar under the cab to read ground speed), its just a pulse that increases with speed…the SF3000 just emulates this using GPS instead of radar… Would be amazing if i could emulate this with AOG …either with a separate arduino or using the autosteer one with a spare output, or machine control… Could do away with the SF3000 all together then!

Any thoughts?

There was some discussion about this on the forum a while back. It’s not a PWM signal. It’s a square wave where the frequency is proportional to the speed. Most sprayer controllers can be calibrated to specify how many pulses there are per some distance. The trick is to get an arduino or similar microcrontroller to generate those pulses. Probably could use some interrupt-driven code to pulse a digital output pin. Some people have talked about using a “Tone” library.

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How delayed would the Arduino’s output be compared to actual radar speed? GPS->AoG->Arduino. Less then a second delay?

This emulated radar pulse normally comes from the GPS receiver. Shouldn’t you consider some add on card on your GNSS receiver board that converts VTG messages to radar pulses? I don’t think it is a task for AOG, none of the commercial “screens” do it as far as I know.

If it is a rare application, one could purchase a cheap stand-alone GPS receiver that comes with the speed pulse output. The speed signal would be accurate (from doppler) even if it was no RTK capable receiver.

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Well he’s already got his standalone GPS unit that’s currently providing speed. He’d like to do everything with one RTK receiver, which is a good idea. Serial output from the F9P can be sent to multiple devices (the TX line can simply go to two places if need be). I agree that a simple microcontroller parsing the VTG strings directly from the GPS and then generating the pulses is the way to go. AOG is not necessary to be involved with this. The microcontroller would be required anyway, and can parse VTG itself just as well.

Yes generating fake radar from GPS does lag compared to radar, and involving AOG would add more latency. Faking the radar signal from GPS is probably fast enough to work okay. A lot of spraying and fertilizer spreaders use GPS-generated fake radar and it seems to be okay.

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I have only ever used “fake” radar, generated from the SF3000 for my sprayer and works great… I agree seems somewhat silly having to go via AOG then arduino…but dont think the F9P has any way of doing this directly… Would just be super neat to have it all integrated, must be many others who have similer systems? Most sprayers etc these days have rate controllers right… ? So must be a fairly common issue …

As @torriem said I have had a working set-up this spring driving my fertiliser spreader.
Arduino read’s speed pgn converts that to a Tone then passes that through a logic/volt convertor, it’s all built on a pushfit prototype board at the moment…so not very good viewing!

And unfortunately I have lost the wee Arduino program I wrote…grr computer hard drives.
The current problem is the way the pgn is sent @BrianTee_Admin was going to look at creating a new pgn for a more accurate fake radar reading.

Has anyone got anywhere with the F9P on this matter?

So far i have been trying to get a speed from COG and SOG using NMEA RCM, and then trying to get some sort of output on the EXTINT pin or TIMEPULSE pin. I have also just tried sending a timepulse but so far that has only worked with a fixed pulse and not one that works with the speed.

if the way to go is to add another card just to make an emulated radar and imuplse, what sort of card would i need to use to do this ?

so far I am having no luck, but I am also very much an amateur. Am i heading in the right sort of direction ? any help would be great !

Don’t think you can get a square wave out of the F9P. You’ll have to use an arduino or some other microcontroller to generate the pulses after parsing the serial NMEA strings from the F9P. As was said before, the arduino tone() command might work to generate the pulses, if the range of 32 to 65535 hz would work for your sprayer controller. Otherwise it would require some interrupt-driven programming to toggle the signal.

A third-party tone library has even more range: Arduino Playground - toneAC Library

Edit: also pretty sure most commercial systems use 5V on the radar pulse signal.

my understanding of the F9P is that a square wave is possible with the TIMEPULSE pin and the EXTINT pin. are these not useable for a synchronization signal for speed ?

referring to the ZED-F9P - Integration Manual figure 36 and figure 42.

EDIT: No it doesn’t look like it’s usable. It’s simply a 1 hz pulse from what I can see. Used for time keeping.

Or maybe such an alternative?

Well sure but he already has one of those. Well not quite, but the same effect. He’s got a Starfire 3000 that he only is using for speed. Would be nice to have something that works with the same F9P he’s using for guidance. Then he could ditch the Starfire 3000 (they are in demand right now if he wants to sell it) and just have one system. But you’re right. The standalone unit is cheap and easy if he didn’t already have the 3000.

To be fair id be open to any cheap solution, I doesn’t NEED to be tied to the AOG setup, although does seem a shame to have to mount another antenna just for speed, but if its cheap, anything is better than the SF3000, sadly I cant sell it as need it on our combine (OEM greenstar system on it) but either way it would save having to constantly move it between combine and tractor in the summer! And save having it on the tractor all the time risking it being stolen (very hot topic for crime these days around here!)

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i have seen a couple posts about impulses per 100m and was wandering if anyone could help me. i am using a ublox ZED F9P and it is currently working well with RTK, but i would like to synchronise it to my spreader with a speed reading from the gps. any help on this would be great !

#edit by admin, I moved your posts to this topic

Were discussing this in another thread the other day, an emulated radar output / speed pulse would be super super useful for rate controllers etc…

I am late to the discussion, but I would like to add I’m in a similar situation. Looking to get precise vehicle speed somewhere, preferably from Agopengps or from the F9P itself. An ESP32 would grab the speed and control the hopper of a seed drill.

Is all you need is a 1PPS square wave? A one half second duty cycle?