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Car Steering Wheel Audio Controls Board - Custom DIY

travisbklein

New Member
what's up everyone, I pulled this board from an identical car to the one I own (2013 Scion xD) to make custom controls on the other side of the wheel, to do control things like DIY LED interior lights and other things.

I'm just trying to understand how the board works, I mean I can read it, see all the resistors, but I can't seem to match it up to the circuit diagram provided by the manufacturer. Specifically I can't figure out which wire is giving this board power and where the ground is.

Wire colors from left to right are WHITE, GREY, RED, BROWN. Images are attached.

Thank you so much for any help.




Travis
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Looking at the pictures and diagram, I'd say the left of the three unsoldered pads at the bottom is the common centre track in the diagram and is ground.
I cannot tell which wire that connects to, you need to check continuity with a multimeter.

The mode switch goes direct to its own pad/wire. It looks like it's the centre unsoldered one (check continuity again to identify the wire).

The bottom right soldered pad is the output from the other switches, the left hand terminal in the diagram.

Whichever is left will be the positive feed for the LED, which is not in that diagram.


If you are reading them from an MCU ADC, I'd check the resistance from ground to the respective button output, see what values you get with each button pressed, then use a resistor to power (+5V or +3.3V) with a value similar to that of the average non-zero value you get.
For the mode button, possibly half the value you see with the switch open.

That should give a reasonable starting point at least, with a significantly different voltage for each button press; you can change it if the voltages are generally too low or too high, to give the best "spread".
 

travisbklein

New Member
wow thank you so much for your help and it is making more sense now! The 4 input buttons vol-, vol+,seek+,seek- all will ready different voltages on the output pin and that is how the the computer knows which button.

When you are talking about the soldered pins I know they mean the 4 pins at the bottom, but when you say unsoldered pads those are the 3 circles above the pins... but are these pads connected to the pins below them? Like is unsoldered pad1 connected to pin 1 I assume? (edit: stupid question obv the vision test says so and a continuity test confirms it)

The wire colors are really not important, they correspond directly to the 4 soldered nodes at the bottom. (from left to right 1,2,3,4) But... the red wire is the 3rd pin which goes along with everything you have helped me see. the supplied image is flipped so it reads pin 4 to pin 1 left to right.


The ground totally makes sense as well as the output pin to read the voltages of the 4 vol,seek buttons.

so pin/node 2 would be Mode, as in the output for the Mode? and node3/Pin 3 would be the constant voltage to the circuit board? It makes sense Mode would have it's own output because holding the mode button it turns off the stereo.
 
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travisbklein

New Member
Ok so I hooked this up to a 5v source with pin 1 as ground and pin 3 as Vcc. LED lights up.

I am unable to get any output reading on pin 4 when I connect any of the Vol or Seek nodes, I must be doing something wrong I think.

I tested the continuity when I connected the Vol and Seek at the 4 outside connections to make sure my connection was good and I was able to get continuity (simulating a button press down on each individually)

When I connect pin 2 to the Vcc, T2 reads 5v. The voltage across the 3 bottom resistors R3 R4 R5 reads 1.92v (voltage drop of 3.08v), for all 3, which is the same at T5 1.92v. Led still lit up.
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
Don't connect power directly to anything (other than the LED) - Some switches short the connections.

The two outputs for general controls and mode need external resistors to +5V.
With those connected, you will see different voltages as different buttons are pressed.

Like I said earlier, the appropriate resistor values depend on the resistors used on the board. I'd try 1K external to start with.
 

travisbklein

New Member
I'm a moron and still learning so please forgive this next part.

Ok so I have 4 pins, and I have a 5v source pos and neg, and I have lots of resistors.

pin 1 = 5v neg ground
pin 2 = pos multimeter for testing
pin 3 = 1k resistor to 5v pos Vcc
pin 4 = pos multimeter for testing (tested individually, not with pin 2 at the same time)

Is this correct what I should be doing? I'm just not sure what "external resistors to +5V. " exactly means

ty so much!
 
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travisbklein

New Member
omg this is so much fun! I just did this for the first time!

Here is how I notated it, (NP) means not pressed, (P) means button pressed. numbers are pins left to right, R numbers are the resistors.

LED - : 1 => R2 => 2
LED +: 3 => R5 => R4 => R3 => LED -

SEEK+ (NP) : 1 => R1 => 2
SEEK+ (P) : 1 => 4

SEEK- (NP) : 1 => R2 => 2
SEEK -(P) : 1 => R6 => 4

VOL+ (NP) : 1 => R1 => 4
VOL+ (P) : 1 => R7 => R6 => 4

VOL- (NP) : 1 => R1 => 4
VOL- (P) : 1 => R8 => R7 => R6 => 4

MODE (NP): 1 => R2 => 2
MODE (P) : 1 => 2

R1, R2 = 100k Ohm
R3, R4,R5 = 700 Ohm
R6 = 330 Ohm
R7 = 680 Ohm
R8 = 2,200 Ohm


Not totally sure what to do next in terms of testing but god damn this was fun ty so much for the help!!!!
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Try this:

Pin1 to 0V

Pin 2 to +5V via a 470 Ohm resistor.

Pin 4 to +5V via a 470 Ohm resistor.

Pin 3 is just a status indicator (or illumination?) and not needed for the switches.

With the meter connected between 0V and pin 2 or 4, you should see different voltages with different buttons pressed?
 

travisbklein

New Member
THANK YOU SO MUCH rjenkinsgb !

I will do this tomorrow after work, and I literally cannot wait.

You are correct the mode button does illuminate exactly as you suspected.

Without seeming annoying, and I do know Ohms law, but I ask what made you want to start the testing at 470 Ohm? Just for learning purposes I'm asking, ty ty ty ty ty
 

rjenkinsgb

Well-Known Member
Most Helpful Member
what made you want to start the testing at 470 Ohm?
470 Ohms or 1K (or 680 ohm etc.) would work, with slightly different voltage ranges.

It's a bit of guesswork, based on the resistor values you listed - using an external resistor somewhere in the range of the switch circuit resistors will mean the two together(selected internal one and external one) form a potential divider that gives an output voltage ranging both above and below half the supply voltage; a decent "range" and easy to measure - and separate the different switch voltages with an MCU analog input.

eg. If the external resistor was 100 ohms, all the switch voltage would be in the 3.5 - 5V range with eg. a 10K resistor would have them all under 1V.

Using something within the max to min range of the switched values gives the best spread of voltages.


Having said that, I just noticed that there are series combinations of resistors and not single values - a higher value may actually give the best range, so stay with 1K to start with. [I'm blaming lack of coffee when I first read your post with the resistor values..]

It's a bit of trial and error, but as long as you do not go too low value it won't do any harm. I'd not go below 470R but that or anything higher is OK for testing to see what voltages you get!

The mode switch will be OK with 1K regardless, that's just on/off, it's the multi-switch output that may work better with different values.
 

travisbklein

New Member
while hooking this up I'm not seeing how can it work if both pin 2 and 4 are connected to the 5v source how can I measure voltages if they are constant?

If I just look at the simple one SEEK+ it's only change is being run through R1 when pressed as opposed to going straight to pin 4.

So 0v is going to pin 4 when NP, and 0v is going to R1 when Pressed then 0v to pin 4, right?

edit: ok so have just did this and testing SEEK+ I go from 5v to 0v when it is pressed, which makes sense because the only variable is a 100k Ohm resistor.

edit again: OMG YOU DID IT! TY SO MUCH!!! my source is 5.2v and if you split that into 4 parts guess what , each part is 1.3v! Check out my readings!

PIN 2 , no change except when MODE is pressed and it goes from 5v to 0v, cause of the 100k Ohm resistor

PIN 4
SEEK+ pressed 0v
SEEK - pressed 1.3v
VOL+ pressed 2.65v
VOL- pressed 4.02v

theoretically I would think we want the greatest distribution/separation in volts, which is 1.3v so the ADC (Arduino) can work the best with respect to PIN 4, right? PIN 2 is easy 5v or 0v.

I HAVE LEARNED SO MUCH!!!! You are the best rjenkinsgb ! I learned all about pull up and pull down resistors and why they are needed, I knew none of that before! I can't thank you enough, honestly, for this learning lesson!
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
Pin1 to 0V

Pin 2 to +5V via a 470 Ohm resistor.

Pin 4 to +5V via a 470 Ohm resistor.
[Except 1K is probably more appropriate, having read your info again]

There is (or should be) no direct connection from the switch board to +5V

With the external resistor in combination with whichever resistor is connected via the button being pressed, the overall circuit forms a kind of switched potentiometer - a variable voltage divider.

The connection between the board and resistor is the divider output "tap".

 

rjenkinsgb

Well-Known Member
Most Helpful Member
PIN 5
SEEK+ pressed 0v
SEEK - pressed 1.3v
VOL+ pressed 2.65v
VOL- pressed 4.02v

theoretically I would think we want the greatest distribution/separation in volts, which is 1.3v so the ADC (Arduino) can work the best with respect to PIN 5, right? PIN 2 is easy 5v or 0v.
That looks great, glad you got it working ok!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Well historically the old piano key VCR's made by JVC (the first three VHS models sold) came with a wired remote. This connected by a single screen cable and plugged in the front via a 3.5mm jack plug, and just like the example here worked by switching different value resistors in circuit - with it O/C when no buttons were pressed.

Now a common fault was failure of the cable, often going O/C or high resistance (poor contact in the cable), and we used to replace the cable and jack plug with a piece of thin mike cable.

Now the moral of this story is about poor design - the design used the highest resistance for Record, so when the cable failed it commonly went to record, instead of what you actually pressed, wiping the tape you were trying to play!

So if you're designing something, give a little thought abut possible failure modes, and design accordingly.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
the design used the highest resistance for Record, so when the cable failed it commonly went to record, instead of what you actually pressed, wiping the tape you were trying to play!
Genius! - or rather a serious lack of forethought!
 

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