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Author Topic: Question about pedal pinouts.  (Read 1040 times)

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Howard_Casto

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Question about pedal pinouts.
« on: July 19, 2019, 02:17:07 am »
Ok So I've been tearing down my new wheel set to document stuff for mods.  I looked up the pinout/color code for thrustmaster pedals and found this:

https://www.iaag66.com/forum/viewtopic.php?f=46&t=2519

Looks pretty straight-forward, but when I open up my TWO pedal set to my surprise, all the wires are there.  On the brake and gas 5v and gnd are connected to the pot pins 1 and 3 respectively with their particular sense wires going to pin 2, but the clutch wire is actually in there and on the ground pin (pin 3) of the gas pedal.  Am I correct in thinking that they just grounded it out so that it wouldn't be floating and causing interference?  So in theory couldn't I add a removable third pedal by de-soldering the clutch pin and soldering it along with 5v and ground to a stereo jack, with ground also connected to the "no plug" pin of the clutch so that it grounds out when the stereo cable is disconnected?  I hope that makes sense. 

On a side note I wonder if my local Radio Shack has 12k pots or if they are useless as usual. 

baritonomarchetto

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Re: Question about pedal pinouts.
« Reply #1 on: July 19, 2019, 08:56:48 am »
I have not an answer to your main question (is the clutch a pot? Doesnt make sense to me), but I think you can use 10K pots in place of those 12K being supposed to be a simple voltage divider. If that is the case, even 5K pots could work.

Howard_Casto

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Re: Question about pedal pinouts.
« Reply #2 on: July 19, 2019, 01:09:41 pm »
Yes, like most cheaper pedals a potentiometer is used to read each pedal... 12k for thrustmaster pedals.  Yes they are being used as a voltage divider, so 5v and gnd are on the outermost pins with the sense line on the middle pin.  The clutch sense line is connected directly to the outermost (gnd) pin of the gas pedal, essentially grounding it.  I'm assuming that is because an unconnected sense wire could potentially give all kinds of weird readings, but I'm not %100 sure. 

I mean I can try things to see how it works but I haven't even had a proper race with this wheel yet.... seems a shame to void the warranty already.  ;)  The plan is to modify a telephone jack to make a passthrough.  That offset on the retention clip of the cable is a pain, but a little dremeling of the phone jack should fix that.  Finding rj12 (6 wire) parts is a pain as well.  I can get them but I'm going to pay a decent amount for them.  I think it'd be cheaper to buy a bunch of regular telephone jacks and cannibalize them for pins to make 6 wire sockets. 

I think you are right about the pot values, but if I understand how a voltage divider works wouldn't I lose resolution by using a smaller value pot?  I've got some 100k (yes you read that right) pots from those n64 pedals but I thought the range is so different that I might get erratic results. 

baritonomarchetto

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Re: Question about pedal pinouts.
« Reply #3 on: July 19, 2019, 02:22:45 pm »
The clutch was the gear shifter in my head, that's why it made no sense to me :D
100K value is common in gamepads. If you will have erratic results depends on the microcontroller. Worth a 3 pin soldering work to test it, in my opinion being that you cannot kill it ;).
Sense pin to ground could be correct if used like a simple variable resistor, not voltage divider (I mean: the clutch will always read low...)
« Last Edit: July 19, 2019, 02:26:15 pm by baritonomarchetto »

PL1

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Re: Question about pedal pinouts.
« Reply #4 on: July 19, 2019, 09:58:37 pm »
Yes, like most cheaper pedals a potentiometer is used to read each pedal... 12k for thrustmaster pedals.  Yes they are being used as a voltage divider, so 5v and gnd are on the outermost pins with the sense line on the middle pin.  The clutch sense line is connected directly to the outermost (gnd) pin of the gas pedal, essentially grounding it.  I'm assuming that is because an unconnected sense wire could potentially give all kinds of weird readings, but I'm not %100 sure. 
Can confirm that leaving an analog input floating (no wiper or ground connected) will usually cause jittering/jumping output values especially if the input port has several inches of wire connected to it.

The wire acts as an antenna.

I think you are right about the pot values, but if I understand how a voltage divider works wouldn't I lose resolution by using a smaller value pot?  I've got some 100k (yes you read that right) pots from those n64 pedals but I thought the range is so different that I might get erratic results.
Technically, there is no "resolution" to a potentiometer -- the output is an analog voltage.
- Corrosion or minor imperfections in the resistive element can cause unexpected variations in resistance ==> jumps in voltage.
- For example, an imperfection causing an unexpected 100 Ohm change will be more noticable on a 5k pot (2% jump) than on a 100k pot. (0.1% jump)

The important question here is whether or not the A/D converter circuit will work with the lower current flow.
-   12k pot draws 0.42mA  ( Amps = 5V /   12,000 ohms)
- 100k pot draws 0.05mA  ( Amps = 5V / 100,000 ohms)


Scott

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Re: Question about pedal pinouts.
« Reply #5 on: July 19, 2019, 11:16:04 pm »
Ok that makes sense, thanks.  I've probably got something of a more reasonable resistance range around here somewhere, but I might just try it to see how it does.  I need to dig up my phone equipment and start making jacks.   

PL1

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Re: Question about pedal pinouts.
« Reply #6 on: July 19, 2019, 11:50:38 pm »
I might just try it to see how it does.
Can't hurt.   ;D

I need to dig up my phone equipment and start making jacks.
Did you search for "6P6C" cables/converters/couplers/jacks?

Cables:
https://www.amazon.com/Robolt-Cable-Modular-Straight-Wiring/dp/B07SLNHHC4/

Converters:
https://www.amazon.com/Telephone-Ethernet-Adapter-Converter-Socket-2/dp/B076MF4F55/


Scott

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Re: Question about pedal pinouts.
« Reply #7 on: July 19, 2019, 11:58:04 pm »
Believe it or not I've probably got some rj12 stuff around here somewhere... being an IT guy nets you some fairly useless stuff... until it isn't useless that is.  My local Lowes has stuff that'll work, but it's a bit overkill rj25... and because it's Lowes the stuff is needlessly expensive. 

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Re: Question about pedal pinouts.
« Reply #8 on: July 20, 2019, 12:39:11 am »
Believe it or not I've probably got some rj12 stuff around here somewhere...
Good.  Sounded like you were going to convert some RJ11 (6 position 4 conductor) jacks/plugs to RJ12 (6 position 6 conductor) by adding two wires.   :lol   :banghead:


Scott

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Re: Question about pedal pinouts.
« Reply #9 on: July 20, 2019, 02:33:26 am »
Hey don't knock it... I've done it before.  I just remembered that I probably have what I need anyway so I won't need to resort to that.  It's less of a saving money thing and more of a I don't want to wait for parts to come in thing. 

Howard_Casto

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Re: Question about pedal pinouts.
« Reply #10 on: July 20, 2019, 11:53:58 pm »
So a word to the wise... I found out the hard way that the pots on these particular pedals tend to spin backwards off their gears when you re-assemble your pedals.  I spent two hours trying to figure out how the hell I broke my pedals by testing my add-on clutch.  100k pots don't work btw and judging by my toner it looks like what little cable I have left has rotted.  Guess it's amazon time.  :(

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Re: Question about pedal pinouts.
« Reply #11 on: August 23, 2019, 12:06:35 pm »
Uh... typical pots are bi-directional.  Meaning... there is no  "Backwards".

 When installing Any pot... you have to make sure it is according to how it is used.

 In an Afterburner analog throttle... the pot needs to be centered by hand, and them placed in the gearing, on that centered position.
If its a little off... its not an issue.  But if you have the pot all the way to an endpoint position... and moved the stick in the direction
that was already maxed out on the pots travel... its going to break the pot.

 In a typical Gas pedal,  the pot often is placed at a the zero point, or close to it.  This could be at either end, depending on how the pot is
mounted,  and how the gearing is utilized to change the direction...  as well as if you wired the pot correctly, or if you wired it in reverse.

 In most arcade games, you go to the test menu, and find the pot value that it expects by turning it, and then lock it down in that
position.  Many games do not mind some default-value shifting... and either have an Automatic calibration system built into the code...
or they include a Calibration option in the test menu  (sometimes both apply).

 With Spy Hunter, that pedal was a much more critical.  If you did have the pedal in the right starting value... the car would tend to be rolling
when your foot was off the gas.  (or, it would travel at warp speed... as it looped the values around).   Actually.. by adding a little to the start
value... it allows for a higher top-speed in-game, and makes the game more fair, and fun. (Most games do not behave that way... as there is
set max speed, programmed into the game... even if the analog value was high than expected)

 Pot mounts tend to have an adjustment screw, and sliding / rotating system, to allow for easy adjustments.  Still... you have to at least
get the thing close to the correct position... as the adjustment only moves a short amount of travel.

 Use a marker to draw a line on the gear at its home position.  And or, spin to each endpoint, and make markings.  And or... use a multimeter
to get the values...etc.