QUESTION
On an older car with one or two contact rings, is there any way to add a function or two? Does each function have to have its own individual contact ring?
With one slip ring today I can operate the horn. When the slip ring recognizes that the horn button has been grounded, that action itself completes the circuit to the horn itself, because 12v+ is always connected to the horn, awaiting the ground signal.
Let’s say I disable the horn as it is now and set it up as one of four functions, each with a switch on the steering wheel. First, do I have to have 12v+ at that point, or can each switch be the ground signal, like the horn is now? And the notion of the resistor network…Am I thinking correctly that at the desired function, like a headlight, I’d have a relay that could recognize the right switch had been activated, so the headlight would come on?
REPLIES
MacGyverS2000
If you make a serial data connection, you only need one slip ring (not including power/ground).
For more functionality, you’ll need a third slip ring. One possibility would be to implement a resistor network. Several switches are placed in parallel, each with a resistor set up in a binary system. No two switches show the same resistance, and any combination of switches can be determined by way of the total resistance shown. You have a ground connection, the third slip ring will be the return signal.
I’m not sure what kind of issues you’ll run into with resistance in the slipring, intermittent contact, etc., but it’s worth a look into for a really inexpensive solution.
The “receiver” will require either a microcontroller or a handful of op-amps set up to detect voltage/resistance levels, so this isn’t an overnight project, but it’s not complicated.
Imagine this setup…
M---Slipring---R1---R2---R3---R4-- | | | | S1 S2 S3 S4 | | | | -----------------------G
Where:
- G=ground
- S=switch (normally open)
- M=your measuring device
- R1=100 ohms
- R2=200 ohms
- R3=400 ohms
- R4=800 ohms.
With NO switches pressed, the slip ring will read an OPEN. If you press switch S1, you read 100 ohm. S2 pressed reads 300 ohm. S3 pressed reads 700 ohm, etc. Combinations of buttons will read as if it was some binary combination of the resistances.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=95893
Above is a snippet.