Automotive gauge display

[Shadyman]

Hi Ian,

I've been mulling over/working on a driver for an automotive dashboard cluster (instrument panel), and I've been looking to your "PC Stats on Analog Gauges" as a reference.

Unfortunately, I don't think there will be quite as many similarities as I had hoped, since car gauges use air-core mechanisms. Many or all of the open-source air core driving products have all but disappeared.

Each of the 6 gauges has 4 pins, though some of the smaller gauges are driven strictly by resistance (12V, resistance and ground pins). (IE, fuel: 0 ohms on Empty, 80 Ohms on Full). The speedometer is driven by a removable circuit board that converts "Pulses per Mile" over time into a speed in MPH. The RPM works the same way, except with engine revolutions. (Proposed victim: http://www.corsicas.com/clusterswap.html)

I'm guessing that each of these air-core gauges can be driven with a sine/cosine-type air-core driver IC, though I'm a fan of software solutions to hardware problems, where possible :)

Could Sine/Cosine gauge driving be done in realtime (processor heavy) or with lookup tables? (Maybe with enough EEPROM?)

Comments? Thoughts? Ideas? Suggestions? :)
Thanks in advance!

[ian]

It sounds like an interesting project, but I'm sorry, I've never even heard of air-cores before now.

I know there are both look-up table and sin approximation algorithms for microcontrollers, that part shouldn't be difficult if you've figured out how the gauges themselves are supposed to work.

[Shadyman]

Ignoring the 9-12V going through the 7805, am I safe in assuming that all this Op Amp work can all be done onboard a PIC? http://bellsouthpwp.net/b/o/bobpaige/Driver%20Schematic%20Dual%20Input.html

[Shadyman]

Though, I also have a newer Chrysler/Dodge instrument cluster (2003), and it's based on (IIRC) a Motorola chip with built-in J1850 VPW decoding. All the lights are LEDs, and it has two VFDs: one 6-digit for mileage (145324) or error codes (P1850) (as well as "Traction" lettering for traction control), and one for what gear is selected (Park, neutral, overdrive, drive, 3, L).

An example of what the dash looks like: http://ww2.justanswer.com/uploads/wmh717/2009-10-04_155813_2001_chrysler_voyager_Dashboard.jpg

And yes, it does get the odometer reading from the ECU; it's not stored interal to the cluster.

So ideally, all I have to do is give it +12V, Ground, and a J1850 datastream. All I'd need to do is figure out what messages to send over the J1850 to get it to display what I want.

I'll probably still end up making my interface board for the older Chevrolet cluster, but I just wanted to throw in another new direction.