Discussion in 'General Electronics Discussion' started by electron86, Jun 20, 2012.

1. ### electron86

1
0
Jun 20, 2012
Hi, I'm a newbie on this forum with a fairly good, but basic understanding of electronics, but as a project I'd like to come up with a steering wheel control adaptor for my car to an aftermarket headunit. Basically the 5 switches on the steering wheel are connected to the headunit via two wires using a resistance ladder. However, the specification for the aftermarket headunit requires a different resistance ladder for the same functions.

So when the resistance on the two wires coming from the switches is say 390ohms, I need the headunit to see a resistance of 16kOhms as laid out below:

Code:
```Function    Steering Wheel        Headunit Spec

Vol +       390 Ohms              16 kOhms
Vol -       0 Ohms                24 kOhms
Mode        3.2 kOhms             1.2 kOhms
<<          1.7 kOhms             11.25k kOhms
>>          850 Ohms              8kOhms```
What would be the best way of going about this? I realise you can buy these as aftermarket, or that I could just replace the resistors in the switches for the required value, but I'd really like to understand the concept of converting between the two if nothing else.

2. ### duke37

5,364
769
Jan 9, 2011
You could perhaps convert the resistance to a voltage by feeding in an accurate current and then use a LM3914 bargraph display chip in dot mode to switch in what resistors you want in the output. Some stable voltages will be required.

3. ### Harald KappModeratorModerator

10,820
2,440
Nov 17, 2011
The relationship between the two resistance series is not linear:

Not something that you can express by a simple equation much less achieve by a simple circuit. Therefore I think the easiest way is to replace the resistors.

Harald

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