Paul__B:
5_Fingers_Left:
Okay, so I have to be sure the cruise control switch sends no more than 5 volts? This can be done with a resistor - 1k or greater?The concept you need to use is a voltage divider.
But what you need to sort out is what the effect of the various switches in the Cruise Control will be, not the same when you disconnect it from its original circuit and connect it to your voltage divider.
5_Fingers_Left:
The output voltage is not important as the Arduino is used to activate 2 x relays and 5v should be enough of a trigger the relays. The Arduino unit does not interact with the transmission ECU - just the up/down micro switches. The Arduino unit is not used in the cruise control circuit, it is isolated from the cruise control ECU. The signals from the cruise control switch can only go one of two ways at any one time; to the Cruise Control ECU, or, the Arduino.I do hope your relays are within the ability of the Arduino to drive them, that is taking less than 25 mA from the port pins. Generally you need a transistor to drive them, preferably supplying them from the 12V supply instead and including the "back" diode across the coil. (Unfortunately I cannot find a clear and simple explanation of such diode).
5_Fingers_Left:
The audio controls is probably a waste of time, but I don't mind having a shot at it. To me, this would be the same as the cruise control switch - just be sure I send no more than 5v to the Arduino input. If the Arduino only outputs 5v or less that's even better - the HU/Stereo accepts a 5v input for steering wheel audio controls. I just program the Arduino to send out signals with greater deviation to the HU/Stereo.The Arduino cannot output more than 5V since its supply is 5V. What you do have to be careful about is ensuring that no device to which you connect it as an output, will apply more than that back. Generally, using isolation transistors and/ or relays.
Voltage divider answers my next question. I had the day off a couple of days ago and checked voltage and resistances at the cruise control switch. I then took those results away and did the whole V over I/R thing to determine what total resistance was required to drop the switches highest voltage (9.7vdc) down to the Arduino's 5v input.
Action - CANCEL
Resistance - 0.330 kohm
Volts - 9.7 vdc (at switch output)
Amps - 0.0294 calculated
Action - SET
Resistance - 1.000 kohm
Volts - 7.4 vdc (at switch output)
Amps - 0.0074 calculated
Action - RESUME
Resistance - 3.000 kohm
Volts - 5.2 vdc (at switch output)
Amps - 0.0017 calculated
I then took those figures and determined I'd need an additional 170ohm's of resistance between the switch output and the Arduino unit to ensure 5v max. Which would give me voltages from each action as follows; CANCEL = 5 vdc, SET = 1.3 vdc and RESUME = 0.3 vdc.
As far as I can tell there are no signals sent back to the cruise control switch.
The two relays I've purchased claim to be for Arduino projects and support 12v. Though I cannot find anything (yet) to tell me what current is required to drive them at the trigger end.
Image of the relays
My plan for the Changeover relay, that switches the cruise control switch output, was to use a more readily available relay. Something I could pick up from the local autoparts shop.
ALL of this would be assembled and tested out of the car first so I can check voltages etc. and to be sure I dont nuke anything.
The Audio Controls part of this project has been abandoned essentially. I believe I might be safer to buy a SWI-X unit from the people at Pac-Audio. I just dont like the bitter taste of admitting defeat before I had a shot at it myself.
Turns out the SWI-X is not how would want to have my controls function. The audio controls project is back on the table.