adding steering wheel switches using horn

I have thought of a circuit for adding switches to the steering wheel using only the horn wire for a circuit path.

It's based around a LM3914 bar/dot  LED driver IC.  For those unfamiliar. It has 1 input and 10 outputs. Each output is controlled by a comparator in the IC.  A  voltage is applied to the chip and is broken up into 10 equal steps by an inbuilt resistor network. eg 1v, 2v, 3v, ....9v,10v. Each voltage step is then applied to one side of a comparator and acts as that comparators reference voltage. The other side of all the comparators is connected to the input of the IC. When the input voltage is equal to or greater than the reference for that comparator then that comparator turns on. It can be set so only one output at a time is on, dot mode. ie Only the highest output on at a time.

My theory is to feed the input for the chip from the centre of a voltage divider. But instead of a fixed resistor as the bottom leg of the divider, the lower side of the divider is fed to the steering wheel via the horn wire. It then breaks up into 10 lines, each with a momentary switch and resistor in series. These are then joined back up to earth in the steering wheel. The value of each resistor is such when a button is pressed a voltage applicable to a comparator is set-up on the voltage divider and appled to the input of the IC. My thought was to add stereo controls to the wheel although one of the outputs would need to drive the horn relay but the horn button itself could still be used. The only limitation is that only one button can be pressed at a time. Not that this is an issue.

There is a kit available is Australia for $7US using this chip as a car voltmeter but can be easily converted to suit my needs so the cost for my circuit is minimal.

Has anyone done something like this before? Any thoughts?

I'm familliar with the bar/dot setup that you are talking about but it's been a few years. We used to use those to make bar graphs for audio before anyone ever saw such a thing. If you clocked the common input, you could convert it from an analog display to a digital one. You kinda lost me in the second paragraph though..Are you aware that the horn button does not have 12V on it but is a switched ground? The horn relay has 12V hot to it and the horn button makes and breaks the ground to toggle the relay. Tell me more..I like this kind of stuff.

Have you seen the new setup that Painless Wiring just came out with? You can have up to 6 wireless buttons in the center of your steering wheel (and still use your horn button) that wirelessly transmit to a receiver under your hood that banks 6 relays. I contacted their tech support and they are supposed to come out with the same setup that responds to a key fob remote.

As for my secod paragraph, I'll break it down.

When 2 resistors are in series between V+ and earth, the value in the middle is related to the ratio of the resistor's values. If you have equal resistors then both drop the same voltage, therefore voltage in the middle is half the V+.  Instead of having just one resistor in the bottom half , have 10 all in parallel and each with a switch. By choosing the right values of these resistors, depending on which switch is pressed puts a different voltage an the middle point . This middle point is then fed to the input of the 3914  chip.

I can send you a circuit diagram if you can use Microsoft word or something like that.

Regarding the horn, the horn wire would be removed from the relay and one of the outputs of the 3914 would now operate the horn relay.

The Painless Wiring sounds good but I be interested in hearing it's price.

OK, I get it now..I thought that you were using the horn switch as the only switch. If I get it, you will have multiple switches in the center of the wheel but you are using the 1 wire originally from the horn and one of the resistive steps will be a new horn signal. And you're right, multiple switches with different resistor values will do just what you said up through the comparitor tree.

I think that the Painless setup is $129.00. They have it shown on the web under Painless.com or Painlesswiring.com.

You've got it! The buttons could be mounted off the hub in one of the vacant spots between the wheel spokes. This would allow the horn button to remain intacted.

Sorry, I'm not always good at explaining things simply.

Why don't you use our SWI-X steering wheel radio control interface. Assuming your horn wire needs a negative trigger to activate a horn relay, all you would have to do is find th lowest resistor value that won't trigger the horn relay when you press your own button. Then you can use resistors above that one value up to a certain value to do the rest of the switches. The SWI-X is a learning remote that can learn up to 12 functions from a button and IR remote, so of course you need a stereo with a remote.

Hotrod send me a diagram shaggy12volt@hotmail.com

Thanks