Steering Wheel Command Center 2

[daveward]

Watching the start of the Indy 500 this morning I saw that the cars had many bells,whistles, warning lights, etc. on the steering wheel itself. This trend is evident with some auto manufacturers, as more functions are moving within direct eyesight and fingertip reach of the driver. Now...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?

Thanks
Dave

 

[MacGyverS2000]

If you make a serial data connection, you only need one slip ring (not including power/ground).

 

[daveward]

To MacGyverS2000, thanks for your quick reply. So in my case, where I may have only one but I think there are two slip rings, one represents the ground connection for the horn button. Assuming I have another slip ring available, let's say I wanted to flash my headlights with a new button A on the steering wheel and flash my taillights with a new button B. I may not have the concept of serial connections in completely in focus... new functions A and B are not related, so they wouldn't be connected serially, right? Or could they? Is there any reference source that you can suggest along with any more clever ideas? Thanks. Dave

 

[MacGyverS2000]

If you have two connections there MAY be two functions in the whel, but I doubt it. The possibility I'm thinking of is using the wheel shaft itself as a ground for both items, but I ave a feeling the shaft will not make a stable enough ground to be useful, which brings us back to two rings = power and ground for something.

For more functionality, you'll need a third slipring. One possibility (don't know why I thought of this to begin with) 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 slipring 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.

 

[mloew]

I am not sure racing vehicles would use slip rings at all. I am nearly sure they use a coiled cable that wraps around the column. Even in WRC cars I think they do that and they have more lock than an open wheel car.

Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[daveward]

To MacGyverS2000 and MLoew...thanks for the ideas. MLoew, I'm sure you're right on when it comes to the Indy cars...they MAY have 1 full turn lock to lock, probably a lot less, so a coiled cable is an easy solution. For my '68 classic, if I used coiled wire I'd have a mess of spaghetti less than two blocks from my house!.

MacGyverS2000, I knew there'd be something clever coming from a guy with that kind of name. Just so we're clear, 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?

Thanks agin to you both. Dave

 

[MacGyverS2000]

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, and R4=800 ohms.

With no switches pressed, the slipring 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.

 

[daveward]

This is VERY COOL. I want one. Since none of my hair-brained ideas I have are 'overnight projects', this will fit right in. A diagram is worth 1,000 words.
Many Thanks. Dave

 

[TaZMaNiaK]

Hi,
I have been planning something similar, which uses my existing factory steering wheel buttons. They use a different value resistor on each switch, and it is a 1-wire connection just like what you have drawn above. My question is about constructing the receiving unit to decode the resistances to trigger different relays. My experience is limited to basic electronics, and I'm not asking for anyone to design anything for me, what I'm asking is if anyone can help me find the information i need to build such an animal.
Thanks a lot.
Matt

 

[MacGyverS2000]

You could do it the hard way and use a handful of voltage comparators, or the easy way and use a micro with A/D capability.

 

[carnage1]

there is a concept in digital to analog conversion called R2R
I will use MacGyverS2000's diagram because I don't know how to post like that.
R1 R2 R3 R4 are all the same resistance and S1 S2 S3 S4 would all be twice that resistance. this gives you an even "step" between each switch. this makes it easier on the circuitry recieving the signal because you have the same margin of error for all of the voltage levels.

if you use an asynchronous ADC with paralell outputs you could hook it to a demultiplexer and directly to the relay's that activate whatever you want.

 

[daveward]

Carnage1: I thought it was important that the R1, R2, etc would all be different resistances, and then using your R2R idea, the S1, S2, etc. would each be double the amount of each corresponding R. Is that what you meant?

Thanks. Dave

 

[carnage1]

yes but I was thinking backwards for d to a you need R 2R for a to d his schematic is good.

there is one piece missing from the schematic and that is the second half of the voltage divider (digital stuff is all voltage controlled)
V---R5---M---Slipring---R1---R2---R3---R4--

untill you press something your reading is 12v
then it is a value proportional to the resistances


R5=100
R1=27
R2=47
R3=82
R4=220

these are all fairly standard value resistors you could pick up eisiely that would give you nearly even voltage drops between the switches.
pressing 2 switches puts resistors in paralell giving a lower voltage than pressing one switch

series resistance = r1+r2
paralell resistance = 1/r1 + 1/r2