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Two potentiometers seemingly connected together by their wipers!

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heliosphan:
Hi All,

I'd appreciate some advice for connecting up a set of pedals from a PC steering wheel controller to an Arduino.

So the wheel is an old Logitech Formula Force GP USB device, and it has a set of pedals that connect to the wheel via a cable with an RJ11 connector (4 pins) on the end.

I've confirmed this connection from the pedals is not USB, in fact it's just to a couple of potentiometers inside the pedals, one for brake, one for accelerator.

The wheel connects to the PC via USB and I've confirmed each of the pedals has its own independent 'analog' value when configured to do so.

I've taken the pedals apart to look at the wiring, so I assumed that one wire will be +3.3v or +5v, one will be ground, one will be the brake pot wiper, and the other will be the accel pot wiper. Maaan was I wrong!

There are Red, White, Green and Yellow wires. Each pot left and right sides have their own wires on the cable, brake I think has Red and White, accel is Green and Yellow.

The pots middle connections (I'm assuming the wipers) are both on black wires, and actually connected to each other! I've measured as near enough zero ohms across them.

Somehow the wheel is able to grab an individual pot value from each pedal, and I've no idea how.

I've wired up an Arduino and I can easily get either the brake or accelerator working by connecting up three wires, generally speaking you connect up red and white to + and -, then either green or yellow to the analog in. For the other pot, wire up green and yellow to + and -, then either red or white to the analog in. This works fine but as soon as I try and get both working, I'm having issues.

I tried using digital ins and outs to sink and source each side of the circuit to read that side, and flip between the brake and accelerator by 'energising' each side in synchro with the analog read, no joy but I didn't use any transistors to do so, which I suspect I should, but I'm not sure how to go about doing it.

Nowhere else on the Internet can I find anybody discussing connecting pots together at their wipers and using the other pins to get all the info they need, it's pretty unique from what I can tell.

I'd appreciate some basic circuit designs that'll make this work.

Thanks!

ledtester:

--- Quote ---The pots middle connections (I'm assuming the wipers)

--- End quote ---

I would verify your assumptions. Desolder the wires to the pots if you need to.

Then draw up a schematic - that will make it a lot easier to communicate what is going on and what you're doing.

tunk:
Maybe you could open the wheel itself and see how it's connected to an ADC/MCU?

heliosphan:
Thanks, yes but I don't want to alter the pedals in any way, if I can figure out the existing method of reading them, I can plug it into my Arduino for rudders for my flight sim, then switch it back to the steering wheel for a racing game. I could use it with the steering wheel and only use the pedals, in fact I'm currently doing this, but its a bit of a faff with lots of cables and big boxes.

Fortunately though, there's a simple connector type they use inside that plugs into each pot. I've disconnected them from both pots then continuity tested them all, including the link between the two wiper connections. These are now just wiring, so I'm 99% certain the wires are where I said they go, but as for the three pins on the pots, now that's where I'm not sure the middle pin really means the wiper - I'm not sure.

Sure I can see that visualising the problem is difficult, sorry I can't provide photos as its a sealed unit and I've put it all back together again now for good. I don't want to crack it all open again with it's hundred screws, and the pots themselves are quite small and fragile and they're mounted to the casing in a terribly weak manner!

All I need is for somebody to go about explaining how I can read analog values from two pots using only connections to the + and - sides of both pots, with the 'wipers' interconnected, if that makes any sense. It should be possible as the wheel does it.

Thanks.

heliosphan:
Actually I came up with a very small schematic, pretty sure this is how its wired up -


--- End quote ---


Pins 1, 2, 3 and 4 go up the wire to the RJ11 connector. Thats it inside the pedal box.

So if anybody can figure out a decent method of being able to read both Pot values from an Arduino, provide a very basic schematic (I should be able to sort out the code) I'll owe you a beer.

Thanks!

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