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Two voltage input, 2 voltage output matrix?

P

puffpio

Golden Member
I want to upgrade my radio in my car to a different factory radio. The pin connectors are identical except that the steering wheel controls operate on different voltages as the upgraded radio has handsfree telephone controls, and the base one doesn't

I want to convert the inputs from my steering wheel controls into the voltage levels that the upgraded stereo would understand

The steering wheel controls has two outputs, they are referenced to ground
The upgraded ratio has two inputs also referenced to ground...

I want to build a 2 input 2 output box that goes inline w/ these two wires
It should look something like this:

http://img104.imageshack.us/img104/2831/untitledbu7.png

Here is the preconditions
1) For the two inputs, they are at 5V when no buttons are pressed
2) the two outputs should be at 3.3V when no buttons are pressed (ie when 5V are coming in on both input lines.

Rules:
1) Vin1 = 0.75V and Vin2 = 5V , Vout1 = 0.7V and Vout2 = 3.3V
2) Vin1 = 5V and Vin2 = 0.75V, Vout1 = 1.3V and Vout2 = 3.3V

3) Vin1 = 2V and Vin2 = 5V, Vout1 = 3.3V and Vout2 = 2V
4) Vin1 = 5V and Vin2 = 0V, Vout1 = 3.3V and Vout2 = 0V
5) Vin1 = 5V and Vin2 = 2V, Vout1 = 3.3V and Vout2 = 1.3V

6) All other unspecified input combinations, Vout1 = 3.3V, Vout2 = 3.3V

I haven't taken EE in a long time..what kind of system do I need to build? Where to start researching?
 
I don't really know much about automotive electronics, but are you sure they arent communicating though a serial protocol or SPI/I2C bus or something? Because those readings seem like a real convoluted way of communicating. Maybe you're missing pullup resistors which may give those strange voltages other than 3.3 and 5 V?


 
according to the service manual, that is how it communicates, when you press a button on the steering wheel, it it puts a different value resister inline to change the voltage...the problem is that the base radio and the mp3 radio operates on different voltages because the mp3 radio has more steering wheel buttons.
My goal is to build something so that the steering wheel controls I have now will work w/ the new radio.

The most straightforward way in my mind (since I am a CS type of person) is get a 2 in, 2 out cheap microcontroller, w/ 2 ADCs and 2 DACs...so that I can do everything in the digital domain w/ a programming language..but it's not he cheapest.

I would like to brush up on my EE and this simple type of project seems to be the best way to do it
 
you don't need a microcontroller to do something so simple, a few logic gates and transistors would suffice. Although, like was already mentioned, that signaling patters seems odd, so I would wonder how accurate that is.
 
it comes direectly outta the factory service manual

there are two wires from the steering wheel into the radio
as an example off the top of my head (not exactly right, but you can get the idea) on the base radio, pressing volume up on the steering wheel sends a 0.75V signal to the 2nd wire...whereas on the upgraded mp3/cd changer radio, pressing volume up sends a 1.3V signal to the first wire.

so between the two types of radios, not only do the buttons send different voltages, but they send them on different wires!
so I just want to intercept them and recognize when I am pressing a button, and then output hte proper signal

Where do you suggest to learn about this stuff? I took EE classes in college, but it's been many years, and I was more CS focused...
can logic gates realy do it? I mean this is an analog system....
 
Yeah, a microcontroller is overkill - but if you're familiar with MCUs then it will likely be the easiest, quickest and most compact way to do it.

You don't really need a DAC though - you could probably do it with a few transistors switching resistors in and out of the circuit.
 
where do you suggest i go read up on this stuff?
I have forgotten almost everything about EE except v=ir and voltage and current laws heheh
 
"where do you suggest i go read up on this stuff?" M.I.T. ?

Binary digital signal levels are spec'd as minimum and maximum for both states for input and output. So, for a given logic family, as many as eight voltage levels could appear on a spec sheet. Have you taken some of these min/max voltages as multiple logic levels?

Because, otherwise, you are describing a pretty screwy set-up. It is POSSIBLE to mux , say, two binary sigs onto one wire which needs four discrete voltages, but it is much less common than just binary.

If it is binary, just shifting the sigs from 5 volt to 3.3 volt will not take more than a RadioShack quad gate and a couple of resistors. Even 4 dinky 1n914 diodes might do it.

 
OK. re-reading the thread.

Lottsa buttons, 2 relevant wires.
Discrete resistor value for each button.
Is function defined by a resistance ratio or discrete voltage levels? If it is a voltage, how is that implemented? Op-amps and bridges in steering wheel?
Data starved problem. Need schematics or full circuit description. Good luck.
 
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