Potentiometer Fun (electronics gurus please help)

[asoap]

I'm trying to build my first machine, and I'm trying to figure out the easiest/cheapest way of hooking up my analog controls.  I went out on the weekend and picked up a Logitech Rumble pad that has 5 analog axis on it.   I took it all apart and the pots have all 3 leads connected.  I'm not by any means an electonics expert, and all of the diagrams i've seen for wiring had only 2 of the three leads hooked up.  So I did some research and found out that with 3 wires hooked up the pots are no longer variable resistors, but dividing the voltage.  Ok.. that's cool.  Then I tried to check the resistance with the controller plugged in, and testing between the outer leads, and I got 60k ohm.  

I was told before that all pots for joysticks are 100k ohm, so did I do something wrong, is it actually a 60k ohm pot?  Could it be different beause this is a USB gamepad?  

So now I'm trying to figure out if I can hook up the pot from a happ steering wheel to the gamepads circuit board.  I'm assuming that if it is a 60k ohm pot on the game pad, that I would need one similar to put into the steering wheel.  Does anybody know of a pot like this or where to get one?

Thanx for the help.

[Minwah]

I am not familiar with the gamepad you have, nor do I know why all 3 terminals are hooked up (although I seem to remember this is the case in a SW yoke too)...

Anyhow, I have just hooked up a 100k pot directly to my gameport for use as a paddle / 270degree steering wheel (kindof).  In order to check what resistance the pot is, you need to test the resistance between the centre in and one of the others.  With the pot fully 'closed'/off it should read close to zero, and the other way should read ?? what ever depending on the pot.  Having said that I just put a multimeter to the two outer pins on my a pot and it gave roughly the same reading.  I guess this makes sense...

Read here, this site is very helpful

http://www.gunpowder.freeserve.co.uk/wheels/potworks.htm

I guess with that said, it sounds like you have 60k pots.  I think this is because your pad probably has circuitry to make it work with the 60k pot - the pot only has to be 100k if hooked DIRECTLY to a gameport.

So I think you have a few options to hook your Happ wheel up:

a) Use one of the pads 60k pots (extend it on wires) on your Happ wheel,

b) Assuming the Happ wheel has 5k pots, you could hack it to a dual strike (see 1Up's SW yoke hack),

c) Put a 100k pot on your wheel, and connect it to your gameport (you can get a USB adaptor if USB is essential)

I personally think c) is probably the easiest/cheapest, but then you already have a pad to butcher so it's up to you...

Please someone correct me if I'm wrong on the above stuff...

Good luck!

[asoap]

From what I've been researching. With the three leads connected the pot no longer changes the resistance, it changes the voltage.

Using the diagram from: http://www.gunpowder.freeserve.co.uk/wheels/potworks.htm

Lead - A would be hooked up to +5 V, and Lead - C would be hooked up to -5 V.  Then if you checked with a voltmeter between Leads-A&B the voltage changes, as the pot is rotated.

Someone told me that I could hookup the +5 and -5 volts right to the 5ohm pot from the happ control, and it would give the same voltage reading.  The only difference is that it would it would draw more current, and I don't know if that is a good idea considering that the game pad gets juice right from the computer.  


So I want to see if what I've been told is true or not.  If what I actually have is a 60 ohm pot, I don't know if hooking it up with 3 wires would change the resistance between the outer leads? Different people have told me that I have a 60 ohm pot, and others say I got a 100 ohm pot.

The reason that I'm using USB is so that I have a lot of analog input, just incase I want to add more analog controls later down the road.

There is no way that I can use the 60k pots (i that's what they are) from the game pad on the happ controlls considering that they are plastic and extremely small.  

I'm pretty sure that I can replace the pots in the happ controls with new ones.  It's just a matter of finding them, (I'm assuming I could one that would fit at a wholesale electronics place).  I just need to know what I'm looking for.

[neuromancer]

Gamepads aren't joysticks. Well sure they are, but what you read about Joysticks having 100k pots, was only talking about joysticks that hook up to the gameport.

A usb controller can have anything in it. The only way to be sure You're getting accurate resistance readings on the pot is going to be to remove it from the board it's soldered to.

That bit about dividing voltage sounds wrong. Suppose the +5/-5 scenario. With the shaft centered, there is 0 volts on B.

If you turn the shaft all the way left, then the voltage from the left side will pass through, but the voltage from the other side will drop according to ohms law. If you have a 1ohm pot, it won't drop very much at all, and you'll still get 0 volts, but a 10 Megaohm pot will greatly reduce it and you will get almost full voltage.

My theory is you will need to closely match the values of the pots on the board, which you will only be certain of by removing and measuring them.

Bob

[Dave_K.]

Neuromancer is right on.  You can' t take accurate resistance measurments while the pot is wired in the circuit (especially when its in series with other potentiometers).

[asoap]

Neuromancer is right on.  You can' t take accurate resistance measurments while the pot is wired in the circuit (especially when its in series with other potentiometers).

When I get home, I'll disconnect it and try again.  And by measuring between the first and last lead, i'll get the resistance, right?

Anyway, the pots are not hooked up in series.  

The game pad has two analog sticks like a play station pad.  The 4 pots hooked up to the sticks are connected to a single board.  That board has 6 wires going to it.  The first wire connects to the first lead of all the pots.  The next 4 wires connect to each middle lead on each pot.  Then the last wire connects to all of the 3rd leads on each pot.

[Minwah]

So disconnect one of the pots and measure its resistance...then try and find a suitable alternative (with the same resistance) from somewhere like Radio Shack I guess or Maplin, RS, Tandy if you're in the UK.

Then you just need to extend the wires from the pad to reach your wheel, and install the pot on the wheel...

[mrhowell]

All this talk about pot is making me hungry.  Where's the Oreos?

[asoap]

Ok.  About this voltage thing and the pots.  I have the controller plugged in right now.  I checked for the voltage between the 1st and 3rd leads, and I got 5v.  Then I checked between the 1st and 2nd leads and got 2.5 V.  I then rotated the pot to one end and got 0.2V.  I rotated the pot to the other end and got 4.8 V.  

[neuromancer]

So based on your description of the wiring, if you unplug it, then all 4 pots will measure 60k ohm between pins 1 & 3. That being the case, then whatever hack you want to make, you need to have a pot of about 60k. It can be a little more or less, since you have calibration software built into the driver.

How much more or less will probably depend on the other circuitry on the board and the drivers.

Bob

[Lilwolf]

btw, original arcade joysticks use 5k pots...

so does the 1up starwars hack.  (using microsofts dual strike controller)...

VERY EASY!

[Xphile]

btw, original arcade joysticks use 5k pots...

so does the 1up starwars hack.  (using microsofts dual strike controller)...

VERY EASY!

logitech wingman extreme also use 5k pots..:-)

although it has one for each axis plus an extra one wired in there (uses a external thumb roller type thing for adjustment on the third pot..)...

hmm..would that extra one be for adjusting sensitivity?  that would explain why I get very little movement in my (arcade cab)space harrier flight stick..
I hacked it using the two axis pots only, and while it shows movement on the calibration screen in the joystick control panel applet, it  doesn't show anywhere near full movement to the edges of the calibration box..:-(

any ideas?