Practically Classics Forum

Either my googling ability or technical knowledge has let me down.
I have purchased a new steering wheel which has stereo and cruise control functions built in. As standard the car didn't have steering wheel stereo controls so there are not sufficient pins in the rotary coupler to wire these down the column. However I was thinking i could "customise" each button to produce a different resistance on the same 2 pins but this is where my knowledge of electronics becomes "sketchy".
Is it possible to build a circuit that would switch a transistor on / off based on a specific input voltage? eg I regulate the input at 10v then apply a 1 ohm resistor for volume up, 2 ohm for volume down, etc?

btw, don't leave leather steering wheels somewhere a mouse can get to them.

Sounds like you are asking for a comparator. Look at designs for the 741 for instance and light/temp level switching.

That looks interesting. Unfortunately I think it is beyond my expertise to make it work so my alternative solution is to add a second ribbon inside the existing coupler. I have just purchased a broken one from ebay (£5) to take apart and measure the space inside. RS stock a range of flat ribbon cables in various widths so I'm sure I will be able to find something that fits with the current one or I could replace it with a ribbon containing more pins.

Hi Terry, do you just want volume up and down or do you want the full station change, etc. functionality too?

Cheers

An op amp is likely to be more reliable than more even finer strands of ribbon cable but I'm just not sure whether Olive realises how limited the space inside the control pad would be for fitting all of that stuff.
However, there's a version of that circuit in the steering wheel of a 2nd generation Renault Laguna and these being not especially sought after, it should be one of thae "just gie's a quid for the biscuit fund" purchases from the scrapyard of your choice.

From memory there are 5 buttons on the stereo controls volume up / down, seek up / down and "mode".
The cruise control has 2 buttons, set / speed up and slow down.
There is also a single wire for the horn that grounds to the column itself and 2 wires for the airbag.
The cruise control is fed by a 0.5amp fuse so not many watts going to the column switches plus some transistors / relays could reduce the wattage for them to almost nothing. I have already relayed off the horn buttons as the contacts on my original wheel were quite badly burnt (possibly caused by the horn fuse being made of a wire bridging across it and one seized horn).

The wheel / switches I have are from a Discovery 2. It has the same boss and very similar wiring which is almost handy. A p38 wheel fits too but has even more buttons i would be tempted to make work so best avoided.
I can either have stereo controls or cruise control as one of the pins which is used for the stereo controls on the disco 2 contains a power feed for the cruise on the RRC. The disco2 taking power for the cruise control from the horn circuit but when I do that with mine, the cruise control doesn't work.

I suppose I could make another timer circuit for the SRS light and disconnect the airbags (I hate airbags they should be banned!). Interestingly if you unplug the bag and go for a drive the SRS system warning doesn't come on but if you unplug the rotary coupler it does.

For multimodes, you could look at dtmf encoders and decoders.