Power/signal to steering wheel, past/present?

[Renate]

I wanted to add some buttons to the center padded part of my steering wheel (no air bag) for control of my on-board Android. A simple Bluetooth BLE HID with 6 buttons would about fit the bill. I already have a PCB with a 2032 cell that I use in other projects. The problem is that for immediate response I can't let it (totally) sleep. I think the current draw to keep it paired 24/7 might be more than I'd want to stick a 2032 cell with. There probably is room for 2 x AAA though.

There is the horn button and I'm sure that I could steal 5-10 mA, with or without a DC converter. The horn relay won't mind.

Anyway, the more general question is, how do they do it? Old vehicles (I believe) just used one contact on a rotating disk to make contact for the horn and used the wheel shaft as ground. Does anything use sliprings? Does anything use flex PC with about 4-5 turns? Does anything use regular cable? How many conductors do they use? Is it discreet or just power and one serial output? Or CAN bus?

[Someone]

Does anything use flex PC with about 4-5 turns?

Thats a "clock spring" in automotive lingo, very common on modern cars (airbag introduction onwards).

[Renate]

Ah, I see that "clockspring" was the keyword that I was missing.