I'm trying to make an interface that controls the right thumbstick on an XBOX controller. I'm pretty sure they are analog and not PWM so now i need to figure out how to either get the PC to output true analog voltage or get a micro controller like my duemillanove to do it. I don't want to go out buying electrical components to make a home made circuit. there should be an off the shelf solution.
yea, i measured it. 1.75 is center 2.20 is one extreme and i can't remember the other. can a digital pot be computer controlled (or controlled by a micro controller) off the shelf?
if its an XBOX 1 controller its around 5k
Yes. You will need to know what resistance the thumb controller is, so you can get a digital pot of approximately the same value.
I need to disassemble the controller to make this mod no matter what. I have no idea how to find the resistance of the thumb stick though. it gets a max of 3v of power from 2 AA batteries and 1.75v is center. do you know the resistance based off of that info?
Using a diode, capacitor and resistor sure seems easier to me than ordering a digital pot and waiting for it to ship to you. You can probably do it with $3 of components from Radio Shack.
that sounds good too. i don't think radio shack has capacitors or diodes anymore though. what should I look for specifically?
This 5K, 256 POS, SPI controlled digital pot looks like it's what I should use: http://parts.digikey.com/1/parts/483863-ic-pot-dgtl-5k-256pos-sot23-8-ad5160brjz5-r2.html
Here's a arduino tutorial for one similar: http://www.arduino.cc/en/Tutorial/SPIDigitalPot
the values for this pot are going to be changing very rapidly and very often. is the SPI interface still a good way to go?
Uh oh, it looks like it might be 10K according to this: http://www.sparkfun.com/commerce/product_info.php?products_id=9032
so then this would be what to get: http://netsemi.com/p-246496-digital-potentiometer-ics-256-step-spi-10kohm.aspx
there is not only 1 type of thumbstick in the world, yes playstations 1 & 2 use10k pots, the microsoft XB1 controllers use 5k (I have one sitting on my bench right now from a 100% microsoft controller)
then to put a twist in all this my logitech XB1 controller uses 100k, SO go get a multimeter and measure it cause if its 3rd party it could be anything, afterall they are just connected to a microcontroller inside the controller (fact on the microsoft design controller its a very small ATmega chip)
that sucks that everyone knows the resistance levels for everything except the XBOX360 POT. I'm pretty sure it is 10K since the guy in one of the tutorials replaced his with the 10K pot from sparkfun.
if you can measure voltage ... why cant you measure the resistance?
(and "some guy" did it does not mean it was correct)
i don't know how. i see it on the multimeter. i guess i put it on 20K since that is the closest setting to 10K but then what? do you measure it the same way you would voltage? or so you do it with the board powered off where by it uses the multimeter power? who knows...
i guess i put it on 20K since that is the closest setting to 10K
yes
you do it with the board powered off where by it uses the multimeter power?
yes
there are 3 pins put a probe on the outer 2
If I was messing with it I would go with Richards suggestion, the pot is just acting as a voltage divider, you can take a pwm signal, run it though a low pass filter made out of a couple passive parts (that yes radio shack sells at your local mall) and just stick it where the middle pin is and the controller would be none the wiser
ok so where do the 2 leads go? in the attached picture mark 1 and to are the pot leads. if i had to guess the red lead on the voltmeter would go on either 1 or 2 and the other lead from the voltmeter would go on ground.. or maybe positive? 
read my last post I edited it
If I was messing with it I would go with Richards suggestion, the pot is just acting as a voltage divider, you can take a pwm signal, run it though a low pass filter made out of a couple passive parts (that yes radio shack sells at your local mall) and just stick it where the middle pin is and the controller would be none the wiser
OK, i can do that if you can give me much more specific instructions. in the pic at the bottom, labels 1 and 2 are where the voltage changes as you move the stick. If you could draw out a wiring diagram with the parts labeled I should be good to go.
ok I measured resistance. see the pic below and let me know what specific diode, capacitor and resistor I need to get.
yes, those pins are directly connected to the pot. the pot is on the other side in the same spot. I was reading about a low pass filter and it was mentioned that the response is slow. that is very bad. the response to the computer input needs to be very fast. at least 30Hz.
I was reading about a low pass filter and it was mentioned that the response is slow.
Just think about that statement.
If you have a low pass filter that cuts off at 30Hz then the response can't be slower than 30Hz can it?
i don't need it to be smooth at all. just fast. it can't be noisy though. the computer is going to be rapidly adjusting the aim for the controller at no faster than 30fps (Hz) so smoothness doesn't really matter.
as an example, it would send 2.20v and then 1/30th of a second later it may send .80v. it needs to be able to adjust that fast.
[edit]Then you probably need an external DAC (digital to analog converter) chip. Like one of these...
http://www.goldmine-elec-products.com/prodinfo.asp?number=A10715
http://www.goldmine-elec-products.com/prodinfo.asp?number=A10711
Note that the "multiplying" DAC may be able to be designed into the circuit directly in place of the original pot. The speed requirement turned this into a more complex project. [/edit]
that sounds better. it is controlled using TTL which is good. the idea of replacing the original pot with this also makes sense. how do I wire it up though. can you sketch out a quick wiring diagram where the controller's 3v supply powers the chip?