Section control on old Hardi sprayer

I thought that I had clear picture about this but I’m getting confused now.

I put a list on things that I think that I need to order:

1 x Relay board, 8 channel? Or is 4 channel really enough?
1 x on off switch to cut off power from relays
4 x on off on switches for sections to manually use them
2 x on off on switch for pressure control and main valve
1 x arduino nano
1 x LM2596
1 x 5 fuse box to protect valves

4 relay board is enough but better take 8 so if relay fails you can change section to working one. More importantly you may find AOG section control 0 tolerance for border over spray annoying that it shuts down entire section for 1cm over the border spray, so you have option to upgrade sprayer to 6 sections, to have last nozzles from either side be separate sections so it only shuts down one nozzle when you are little bit over field border.

You need to have 4PDT switch to cut power to relays as @Larsvest suggested to prevent backfeed and prevent possibility to have both motor directions accidentally powered if you forget to turn off manual switches.

So every section switch needs to be 4PDT and wired separately to cut off power from relays?

No 4P means 4 positions so it will cut power to 4 relays from one switch. Or you can have 4 on off for evry relay 12v+ cheaper option less convinient.

You can also make those two extra sections(eg. 20 cm) in AOG but without connecting them in real life. Sprayer still spray 24 m (or what you have) even when AOG shut off outer 20 cm

Ok I see. So one 4PDT switch to cut power from relays so switching from auto to manual. Then just DPTP switches for every section.

Thats good way to do cm of border overspray if you drive fast and manually you can doble it if you add those 2 true sections. Especially good on trapezoid / curved field borders.

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There are Arduino codes and circuits on GitHub.
These circuits provide stand alone functionality and section control by AgOpenGPS. I’m using this for 5 years now.
There is feedback to AgOpenGPS in Auto and manual mode.
So simply take this.
You can realise it on a simple home made pcb or buy one. (Prototypes available)

Link to GitHub:

Video about function (2 years old but still the same) with my control box for a 1994 Rau D2:

example for 4 sections vineyard sprayer with motor pressure adustment

For this you need
Main switch: (on)-0-(on)
Pressure switch: (on)-0-(on)
auto/man: on-off
sections: on-off
relays for 2 wire motors: DPDT for 3 wire: SPST or SPDP


I now studied the original control box with voltage meter and there is only 2 wires per motor. So when you click the switch ground and 12v switch places. Doesn’t this make it so that it is not possible to use this configuration with only 4 relays?

Yes for 2 wires you need to have 8 to switch 12v+/ground.

hello @MTZ8302

I really like the secion control you build. I’ve been reading your github but i do have a question before I might build one myself too.
I have a V4 micro PCB and use a UDP network in my tractor for all the different PCB’s, I know you have a version with the ESP32 with Wifi but is there also a possibility to use an ethernet cable? for example with a nano and an ethernet shield connected to it? Or will there not be enough pins to connect the sectioncontrol and the ethernet to?

Hi EFlonk,

the number of pins needed depends on your sprayer: how many sections, rate control (manual, by +/- motor, via flowmeter), maybe boom control.
The ESP32 code supports Ethernet (not tested with actual libs) with a W5500 chip. I use this version:

If you have some more time, some guys from the developer group are about to draw a PCB. I made one for vineyard purpose (2 sections, 2 fluids, 2 pressure controls manual +/-). Feel free to build a PCB by yourself. I also did this with a prototyping board Arduino UNO format, that I put on top of an ESP32 in UNO shape.

WiFi works good, if you have a direct access to the PCs Ethernet port. Routers cause delay. My setup is like this at the moment: PC - ESP32 w5500 - WiFi (same ESP32) - section control. See:

I’ve built a couple of versions of the hardi control box. The motors are just 2 wire and I use a dpdt relay to switch the signal between high and low on each wire. For the master on-off when using agopengps i use diodes on each section connected to the master relay so once any section is on master will be turned on and when last section is off master is turned off. Some hardi sprayers don’t have master on/off only section control.

Good evening, thank you.
I started with the GPS autosteer, I got that working and the “normal” section control is finished too. So i’m looking for my next step up.

our sprayer is 7 sections with a +/- motor, I’ve already made a seperate boom control, but that could be integrated into one PCB.

I’m curious about the PCB thats being developed, altho it might be a cool thing to do myself too, and to learn something about designing a PCB. the section control you showed in your YT video’s was that still a breadboard kinds setup? no PCB made for that?

Have u built sc for hardi hc5500 with 5 sections?

you also have this solution…

i built one for 6 recently but you have to be careful does it have rate control?

It does but we don’t use this function… I have read from CERA forum that the other functions will freak out if u use external SC, because it dosen’t see sections turing off.

yes i ran into that problem - I have a hc5500 i want to reverse engineer when i get time. It looks like your switch box needs to send section data back to the hc5500 computer(jobcom?) over the 25pin data connector. it looks like there is a wire for each section. If you are not using rate control no issue - my solution is to build a pass through box so a hardi male and female connector with a set of relays between - no switches need - use the original switches on the hc5500 to control on off but let aog force on. Forgive my drawing but hopefully gives you the idea

Do you have a link to this information on the cerea forum? I have a Hardi with HC5500 and need section control.

I thought it was ok to just use relay switching, since it’s a calibrated reflow system and the flow is the same regardless of the section being on or off?

My HC5500 actually has Jobcom which allows serial control from my Trimble monitor. I have worked a bit to reverse engineer the protocol, and am fairly confident that I can do it, but I lost momentum on the project. I’ve been using the sprayer for a couple days by flipping switches and I really miss section control. I want to do something quickly, I thought relays would be easier.