# Thread: Connecting resistive "steering wheel media buttons"

1. The FB is powered externally. This is by design as we realize most people are pushing their usb ports to the max in the car, and the last thing you want is a daisy chain of random USB hubs. So it accepts between 7/8 volts to about 15/16v. That voltage is what is sent out the digital output ports as well. So if you power it with the 12v rail of your PSU, then the output volage will be 12v from the digital output ports. If you power it via the car's unregulated 13.8v supply, then you will get 13.8v out of the digital output ports.

2. And to the OP, if yours puts out varying resistance compared to buttons, not voltage, you need 1 or 2 resistors as explained below. These values are from a 7th generation Honda Civic and will not be the same on your car. You need a multimeter that can measure ohms.

If when no buttons are pressed you get a reading, that should be the smallest resistive reading. This is 100ohms. Now that is the smallest value. Because of the nature of the voltage divider, and we are trying to go from a maximum of 13.8v to a maximum of 5v and that 100ohms is the R1 in the voltage divider, that means the second resistor R2 (That you need to buy) has to be roughly half of that so 50ohms.

If you push no buttons and get a reading, you only need 1 resistor as is the case with the 7th gen Honda Civic. If you dont get a reading, or the reading is low (like less than 100ohms) attach a resistor between the R1 and where the FB connects like the last image #3.

So when you have no buttons being pressed, you will get 4.597v registered on the Fusion Brain. Now there are quite a few buttons, but the highest value button is 3.7Kohms, or 3700 ohms. So now R1 is 3700 + 100 (the way the civic is designed. The 3700 is from a schematic. If measuring in the car, you will only see 3800, because the initial 100 is already added to that measurement). R2 is still 50ohms. So now you have this:

So when that 3700ohm button is pressed, the FB will measure 0.179 volts.

Now these voltages and ohm values are approximate. When you buy a resistor, they are labeled with tolerances. Usually 10%, 5%, 1%, or 0.1%. The higher the tolerance, the cheaper the part.

What that means is if you buy a 100 ohm resistor with a 5% tolerance, what you are buying is guarenteed to be between 95ohms and 105ohms. So any value of 95ohms, 96ohms, 97ohms, 98ohms, 99ohms, 100ohms, 101ohms, 102ohms, 103ohms, 104ohms, and 105ohms is acceptable (and of course there is the infinate number of decimal numbers inbetween like 100.4543ohms and so on).

If you buy a 100ohm resistor with a 0.1% tolerance, you are guarenteed to have a 99.99ohm resistor to a 100.01ohm resistor.

And if you cascade 2 resistors of 5% tolerance, you will be at worst off by 10% in your calculations if each were off by the maximum of 5% and so on.

But the beauty is the value wont change once you buy it. It will always be wrong by x% where x is between 0% (dead on from the factory, exactly as described), and Tolerance% (the worst they are allowed to sell at that tolerance).

So do the voltage divider calculation with your exact values as measured by a multimeter, and that will be what you use.

Make sense?

Image #3:

3. Originally Posted by 2k1Toaster
What resistances do you get?
Thanks for pics they help alot

Range Rover does it differently !?!
NOTE STEERING WHEEL IS CONNECTED TO GND
POLARITY REVERSED

Y = Steering Wheel Resistors
X = Output Voltage
Conected as above I get the following voltages (NOTE POLARITY IS IN REVERSE TO YOUR DIAGRAM)
Button UP / Y = 3 ohm / X = 4.26V
Button DOWN / Y = 400 ohm / X = 1.17V
Button MODE / Y = 5.1k ohm / X = 0.12V
Button VOLUME UP / Y = 9.8k ohm / X = 0.06V
Button VOLUME DOWN / Y = 25k ohm / X = 0.02V

You mentioned that the brain is already grounded, as the polarity is reversed on my system can I connect both + and - to brain so it works?
Or should I connect in a different way?

Range Rover Steering Wheel Circuit Diagram

4. Please connect the multimeter (-) to ground, multimeter (+) to between 50 ohm and 100 ohm, and re-record measurments.

5. Originally Posted by greenman100
Please connect the multimeter (-) to ground, multimeter (+) to between 50 ohm and 100 ohm, and re-record measurments.
Connected like this:

I get:

Y = Steering Wheel Resistors
X = Output Voltage

NO Button pressed X= 13.87V
Button UP / Y = 3 ohm / X = 9.47V
Button DOWN / Y = 400 ohm / X = 12.67V
Button MODE / Y = 5.1k ohm / X = 13.64V
Button VOLUME UP / Y = 9.8k ohm / X = 13.81V
Button VOLUME DOWN / Y = 25k ohm / X = 13.85V

Please note that my steering wheel is connected to '-' NOT '+'

thanks again

6. If you are removing the HU, and there's no external 12V source in there which there shouldn't be, use this. Should be a little easier to understand.

7. Originally Posted by Curiosity
If you are removing the HU, and there's no external 12V source in there which there shouldn't be, use this. Should be a little easier to understand.
THANKS
That makes sence
It will reduce voltage to 5v when no buttons are pressed

Now I get:
Y = Steering Wheel Resistors
X = Output Voltage
NO Button pressed X= 4.84V
Button UP / Y = 3 ohm / X = 3.7mV
Button DOWN / Y = 400 ohm / X = 0.74V
Button MODE / Y = 5.1k ohm / X = 3.38V
Button VOLUME UP / Y = 9.8k ohm / X = 3.96V
Button VOLUME DOWN / Y = 25k ohm / X = 4.45V

Still like to know:
The board has a 5v supply, can i use that, instead of tapping off 5v from a usb lead?
Whats the smallest voltage difference the brain can detect? (3mV?)

Thanks again

8. ## Coding

Now that I have valid analogue inputs, I would like the brain to convert these to key sequences:
IE:
X = Output Voltage
Button UP / X = 3.7mV / Send hotkey 'ctrl'+'alt'+'a'
Button DOWN / X = 0.74V / Send hotkey 'ctrl'+'alt'+'b'
Button MODE / X = 3.38V / Send hotkey 'ctrl'+'alt'+'c'
Button VOLUME UP / X = 3.96V / Send hotkey 'ctrl'+'alt'+'d'
Button VOLUME DOWN / X = 4.45V / Send hotkey 'ctrl'+'alt'+'e'
NO Button pressed / X= 4.84V / (Do nothing, Dont send hotkey)

Can you please give an example of how to code skin?
>>AI_INPUTS
#STARTNEW#
#NAME#SteeringWheel
#TYPE#???
#VIDPID#MyBrain0
#???
#ENDNEW#

Thanks again for all your help and prompt replies
(Waiting on delivery of brain - want to be setup when it arrives)

9. What program are you using that you need such elaborate key commands? Usually it is just up or down, or a simple letter like "z" or "c" or something....

10. Originally Posted by 2k1Toaster
What program are you using that you need such elaborate key commands? Usually it is just up or down, or a simple letter like "z" or "c" or something....
Centrafuse™
http://www.fluxmedia.net/

You can customise, so it doesnt have to be so elaborate.
Is there a problem sending multiple keys?
If so, I would setup to send only 1 key

thanks

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