Help with hooking up steering wheel controls

bigbuffs · 03-09-2008, 08:29 PM

OK so I have been planning on how I would integrate my SWC's for a long time and I did a lot of searching to figure out how to do this. Since I didn't know much about electrical stuff (I know a lot more now but still need a lot of help) I had to read things several times to get a good idea of what I was doing.

OK my original plan was to get a gameport and use God_of_CPU's method but I couldn't get the port to work at all. But, It seems like some people have wired right into a USB controllers analog stick and used that method.

Since I have a spare controller I hope to use this method but I need some help on understanding how to do this.

I have a 2000 grand prix and it uses 1 wire coming from the SWC buttons. There are eight buttons total. When no buttons are pressed the voltage reads 0 but on press of any button the voltage goes to about 14.

Now when I measure current (the A setting on my multimeter I think is Amps which I believe to be current) each button press ranges in value.

SEEK UP=4.61
SEEK DOWN=3.34
PRESET=1.05
AM/FM=2.15
VOL UP=11.18
VOL DOWN=9.09
PLAY=7.45
MUTE=5.97

Can anyone help me figure out what this stuff means and how I can integrate it. Thanks

Curiosity · 03-09-2008, 10:15 PM

That doesn't look like amps. Don't switch to amps until you understand it. It's basically like replacing a wire with a meter to measure current. Over 10 amps will blow the meter or it's fuse if it has one.

First you should figure out where the power is coming from. Disconnect the radio and see if that does it. With a gamepad/joystick, you'll need to drop the volts to 2.5 or with fusion brain, 5.0 which is much easier, so the unregulated 14+ is a little harder to work with. If you can remove that and replace it with the 5.0 from the gamepad it will be as easy as adding a couple resistors. Otherwise it's less safe. God_of_CPU uses a diode to block it and reverse the current but I think you need both wires to work with.

bigbuffs · 03-09-2008, 11:41 PM

Well I'm not 100% sure I know what each setting is on my multimeter but it looks just like this one. It is set to voltage and thats what measured 14 each time I pressed a button. Then I just went around the wheel on the multimeter and tested the wire for any reading changes. The 20m under the A- setting gave me the seperate readings for each button press. I believe that setting measures current.

The radio is already disconnected. I tried putting a diode on the wire but that stopped me from getting any readings all together.

2k1Toaster · 03-10-2008, 12:08 AM

This might be just what you are looking for: http://www.mp3car.com/vbulletin/docu...-controls.html

Curiosity · 03-10-2008, 12:08 AM

Yes, that would be milliamps. Don't use it. Just use the 20V setting. Do you have the black lead of the meter connected to the car's ground? Do you have any resistors laying around?

bigbuffs · 03-10-2008, 12:28 AM

Quote: Originally Posted by 2k1Toaster

This might be just what you are looking for: http://www.mp3car.com/vbulletin/docu...-controls.html

Ya I saw that thread but it's not quite what I'm looking for. I don't have the FB, I'm trying to run my SWC's through a USB controller if this is possible anyway.

I think I used the cig lighter ground when I tested it. I do have some resistors I think they are 470 ohms

2k1Toaster · 03-10-2008, 12:40 AM

Well for measuring the voltage accurately, and getting a 0-5v scaling voltage, it is what you need. What you use to get it into the computer is up to you, but the getting it ready part is the same.

Curiosity · 03-10-2008, 02:34 AM

Yep. FB would be easier too.

Just putting a 470 ohm between the two inputs on the meter will allow you to see volts when pressing the buttons. Using the divider will drop the volts to a safe range for the FB or gamepad, but the gamepad will need an input of 2.5v when no buttons are pressed because it will calibrate a center position. For the FB it would only be like
SWC--/\/\/\--<input>--/\/\/\--Gnd

basmoq · 03-10-2008, 11:31 AM

ok, to simplify things for you a bit, what you need to do is disconnect the SWC from the car completely. It is a two wire system and is nothing more than a bunch of resistors in parallel with a momentary touch button breaking the lines between all but one resistor. when no buttons are pressed, you are going directly through one resistor. When you press a single button, you are allowing the current to go through two resistors in parallel. To calculate the resistance of each resistor in the circuit, you first disconnect the leads. Next make certain that your voltmeter has a good fresh battery and set the meter to reading resistance (Ohms). Typically you will be in the 200 to 2000 range, so start small and go up on the voltmeters dial as necessary. Now hook the red lead to one wire and the black lead to the other of the SWC. Now you are measuring the resistance of the "always on" resistor, write that value down, you'll need it soon. Next, you need to press each button and jot down the value for that button on a seperate sheet of paper because it is NOT the value of the resistor under the button you are pressing... To get the value of the resistor you are adding to the circuit (in parallel with the Always On resistor), you use a derivation of Ohm's Law, 1/Rtotal = 1/Ralwayson + 1/Rbutton. Now you should be able to do anything you want with the circuit, because you know what the resistances are, and can calculate what values you will get out given a specific voltage, again using Ohm's Law. If you would like to cheat and use a calculator, go to the PAC website, they manufacture SWC to HU controllers and have a nifty calculator on their webpage, along with diagrams and such. I'm in the process of replicating the factory SWC for my Subary Outback using the blank plastic piece where the buttons should be.

bigbuffs · 03-10-2008, 01:31 PM

I see what the setup for the fusion brain would be I think anyway. Would it be the same for hooking up to the controller (building a voltage divider just need to lower the voltage)?

Shouldn't the Voltage be different with each button press? I get the same reading every time for each of the eight buttons 14.2.

I don't think that I can get the SWC wire out of the car. I would have to rip apart the steering wheel I think and I'm not sure I want to do that and if it is really necessary.

I think I'll try to build a voltage divider with the resistors I have and see what type of measurements that gives me.

bigbuffs · 03-10-2008, 01:58 PM

OK so I think I'm getting somewhere now. I built the voltage divider and hooked it up and tested it and now I get variable voltage readings. I still get 0v when no button is pressed but now the readings are as follows

SEEK UP=1.34
SEEK DOWN=1.04
PRESET=0.37
AM/FM=0.71
VOL UP=2.45
VOL DOWN=2.17
PLAY=1.90
MUTE=1.63

These values are actually a little higher. I retested the voltage with the car running but still only 2 go above 2.5 volts so I think I can definitely work with this.

Curiosity · 03-10-2008, 02:39 PM

Well, I hope they don't vary by 0.3v or they will overlap each other's values. The reason you get 0v is because it's an open circuit when no buttons are pressed. You could hook it up to the fusion brain right now and have it working. Well done! The problem with the gamepad is that it needs 2.5v at startup. I really think you can get to the wires. They are usually under the steering column. It's 2 wires in a sleeve. Not the yellow one. That's the airbags. Don't want that going off.

I guess if you have to, a 2.2K resistor from the car battery to input, input to 470 to ground gives 2.5v from 14.2v, then pressing the buttons goes up, but what are the resistor values there? It's hard to guess at this stuff.

bigbuffs · 03-10-2008, 03:35 PM

I think I see what your saying. The axis on the controller needs to be at 2.5v when the controller is plugged in or started or whatever. And then the the voltage varies from 2.5v either plus or minus 2.5v depending on which way the analog stick is pressed.

Couldn't I just wire my input into the x or y axis on the analog stick? wouldn't that allow the controller to see 2.5v at start and then change depending on which button I press?

basmoq · 03-10-2008, 03:49 PM

I would highly recommend taking off the steering column shroud and just tapping the two wires at the roll connector, this way you are certain of all the resistor values, and have less parts involved (less parts = less chance things will go wrong). Also, try measuring those values when the car is running and see if they change when you hit the gas... I bet they will. It's always better to isolate the circuit and run it off your own power source from my experience. Just my opinion

bigbuffs · 03-10-2008, 03:54 PM

OK I think I'll remove the fuse for the airbag and then see what I find in the steering column.