General car steering wheel question

Sort of related to the thread about why they moved the headlight dimmer switch

Buttons mounted on the steering wheel (not talking about the stalks) often control the stereo, cruise control and firing the airbag. Probably more on newer cars. Lots of stuff going on there.

I’ve seen on older cars that the horn is connected electrically through a copper disk on the wheel, and a disk on the column. Compress the horn and it makes contact and honks the horn.

Is all this new stuff controlled through some ‘hard’ contact too? Wires? Or is there some sort of wireless control going on?

I ask because after years of turning a wheel, I would imagine that any direct wires would not last and ware off the insulation.

they use a “clockspring.”

http://www.supermotors.net/getfile/288140/fullsize/clockspringexploded.jpg%20alt=

http://forums.nasioc.com/forums/showpost.php?p=37371377&postcount=8

Huh. So it is hardwired. Surprised that it can handle hundreds of thousands of miles and temp differences of ~150 degrees. Materials science, quite the thing. With RFID, I thought it may be easier to do it that way.

Sort of like the notice that a tire is low on pressure.

Wow*!* That’s really cool*!* I like to consider myself still knowledgeable about cars so I’ve occasionally wondered about this too (but not enough to ask). I’m glad to know the right answer now.

There’s a button for firing the airbag?

Are we supposed to test it every month now?

Another way to minimize the number of wires that needs to run through the rotating part of a steering wheel is to use different resistance values for each button function.

The stereo controls on the steering wheel, like Volume up, vol down, mute, track forward, track back, answer call, hang up, etc. all share the same pair of wires rather than having a wire for each function. Pressing Vol + connects resistors together across that single pair of wires and the head unit in the dash sees, for example, 35 Ohms. Pressing Vol - shows the head unit 47 Ohms. The head unit interprets the resistance presented and the music gets louder or softer. My car also has cruise control buttons and more buttons to control the information display. That’s something like 16 buttons in total.

If you replace your stock stereo head unit, you can buy a device that interprets your factory steering wheel controls and translates it to whatever the your choice of new stereo unit understands as remote commands. Pacific Audio Corporation is the first that comes to mind, but I’m sure there must be others.
http://www.pac-audio.com/

Depending on the make model and year of car there are several different ways information is passed. Some cars use resistors as mentioned. Some are individually wired. Some have smart switches the uses local interconnect network (LIN) with digital signals to reduce the number of wires.
In all cases the airbag has its own dedicated wires for diagnostics and firing.

Try pricing a replacement steering wheel - you will be shocked.

Isn’t the airbag symbol on the steering wheel just to inform the driver where the airbag will come from if it’s activated?