vultan

I have a 1995 Range Rover HSE, - the resistive steering wheel buttons are grounded.
If I connect a multimeter to earth and HU, I get different ohm readings when I push different buttons. When I connect the multimeter to "+" and HU I get the same 12V reading no matter which button I press on HU???
I should be getting different voltage readings?
Am I doing something wrong?
Can fusion brain (analogue inputs) detect different resistances, or does it need to see changes in voltage?
Any help would be greatly appreciated
thanks and confused
Peter

MP3Car.com

 

2k1Toaster

It needs to see voltage differences. However, you can make a Voltage Divider so that the voltage is never over 5v. I would use 14.4v as the input voltage because it should be 13.8v but some higher output alternators use a 14.4v system. But if you know you have a 13.8 system, then you can use that, but other readers should know that they need to check first.

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vultan

I cant see how this will help, as I get the same output voltage no matter which button I press. Wouldnt a voltage divider just drop the voltages, giving a lower voltage that is still the same no matter which button I press?

2k1Toaster

Think of it this way. You already have Vin and the first resistor. So you need 1 resistor tied to ground, and you measure between the two.

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vultan

Thanks for your input - I think my multimeter is faulty, I will check that out first.

bigbuffs

I'm wondering the same thing here. I've been talkin to the people on the FB site and they say that it measures up to 5v. My car has 1 SWC wire that varies the voltage for each button press. The lowest reading is 1.05 and the highest is 11.18. would I be able to hook up to the FB and still have function of all buttons? i'm reading about voltage dividers right now.

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2k1Toaster

If the voltage changes between 11.18 and 1.05, then you are golden with a voltage divider.

Use 1kohm and 2kohm as your 2 resistor values, and you will get this as the maximum:


And for the 11v button press:


And for the 1v button press:


And of course the rest of the buttons will be inbetween the 11 and 1 output. The voltmeter in the images would be the Fusion Brain essentially. You only need the 1 wire into U1 (The Fusion Brain) as the FB is already grounded, and you dont need the +5v power. So it is a single wire connection to the FB.

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2k1Toaster

What resistances do you get?

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bigbuffs

OK that won't be to hard. Could you explain the diagram a little more to me.

I understand most of it but VCC is the wire running from my SWC's right. Then I put a 2k resistor in and the splice into the wire and send the splice to the FB (analog input). After the splice I put a 1k resistor in and then ground the wire? Does that sound right?

Also another question about the FB. Is the FB powered by the USB port or does it require an additional power supply?

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2k1Toaster

Yes, VCC is just notation for a power supply, which is in this case varying from that wire (technically not true, but the concept holds true for something like this). So that wire you used to measure the 11v-1v is "VCC" and then you need to buy 2 resistors (I picked common values so you can buy from RadioShack for example). Those 2 resistors, just need to be the correct ratio. You could use 10kohm and 20kohm, or 1Mohm and 2Mohm, and so on it makes little difference. I suggest 1kohm, and 2kohm though as they are simple to find and cheap.

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2k1Toaster

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.

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2k1Toaster

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:

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vultan

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

greenman100

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

vultan

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

MP3Car.com