Contour Enthusiasts Group Archives Forums Modifications General Mods need help on making digital gauges

So I just finished my microcontroller lab for the semester and I'm pretty motivated to keep doing work with them. I was gonna recontent my clock but I decided I want to put a two line LCD in that spot and wire it up to a microcontroller(probably a PIC16F874.) On one side I would have the time, and on the other I'm thinking of displaying two vitals that can be changed to whatever is available and desireable.

My question is, what do you guys think would be the best approach for this? Tap into some sensors on the car or read up on ODBII and tap into that? I think ODBII might require more programming, but easier as far as plug n playability.

The stuff I display isn't that important to me. This is more to keep myself occupied and do something different(Although a voltmeter is a must, no more running around with a dying alternator for this guy.)

Thanks,
Chris

Hmm. Oil pressure, MAF voltage would be two that could be very usefull if you new what you were looking at.
Maf sensor voltage can be correlated with airflow volume. If you get a copy of the maf transfer function then you can interpolate the airflow in grams or pounds per minute. This can tell you if you are saving gas or not. For performance it can tell you if you are pushing the amount of air that you think you should be and let you know if you are maxing out your sensor.

Tapping the sensor wires would be far easier. If you try the obdII route I bet you never get it done.

most sensors on the car work on a 0-5 volt reference.
The MAF has four wires but you only need the signal and ground
Oil pressure is a variable resistance sensor so you can read voltage as a function of oil pressure. This one can be all analog and no microprocessor required other than to drive the led numerals I guess.
The MAF one will be more challenging because you have to have a lot of data points since the curve of airlfow versus maf voltage is not linear at all. Looks more like a third order polynomial.

Best approach would be to use the OBDII port. You can get an IC that will convert the PWM Ford signals to a RS232 serial interface sutible for a PC. (ELM350 or somthing like that...dont remember). Then learn how to do serial communincations with the pic, and all you need to do is send a string on the comm line and the computer will respond with the reading. Then just translate the reading to your display.
This approach is probably easier to program as you don't need to store transfer table info, and you don't require using a pic with an ADC onboard. Also with the OBDII if you decide you wan't to display something else, it's a lot easier to pull the micro out and reprogram it, than to rewire to another sensor. You could also have a button to cycle through different stuff if you wanted.

Hmmmmm....now you've got me thinking about doing something similar.

Here's the IC ELM320

This is all great info guys, exactly the kind of stuff I was looking for. I'm gonna start researching all the details when finals are done in a week. We had a lab where we exported data via serial port, so maybe I could figure out how to import it as well.

Here is another question on OBDII. Is the data lagged at all? I remember when my bro had his laptop hooked up to my ODBII and reading RPM's. The data would come in more than 3 or 4 seconds after I had already hit that point.

If you read through that data sheet, there is a section on packet data or something. Using that mode can be used to increase the data transfer rate between the pic and the obd2. It should decrease the delay time a bit, I don't know by how much though.

So this is getting ahead of myself but I wanted some feedback on the idea I just had. What if some lighting I had in the car(under the dash,door handles, cup holders, etc, I dont have any but what if...) shifted colors after a certain RPM?

For instance I was planning on having some soothing blueish-green LED's in my door handles to match my indiglo gauges. That's nice for calm driving, but what if the lighting shifted to red or something at higher rpm's?

I guess it just sounds like a complicated shift light of sorts. I was thinking more along the "mood lighting" aspect. High rev's = extreme driving = red lighting

Obviously that's more of a marketing slogan to 17 year old ricers, but you get what im saying...

I'm just trying to think of more things to have my microcontroller do. I'm also planning on mounting it where the clock should be ala mondeo:

Judging by the last time my bro pulled out the odb2 scan program on his lappy, aren't there a really really ridiculously large amount of values that could be pulled?