The instrument pod that bolts to the steering column
is a bit clunky, so I an looking at it, thinking it could
be replaced by something sleeker.

It has a few functions:
- Analog tachometer needle.
- LCD displaying the outside air temperature.
- 6 light bulbs.
- variable brightness back lighting.

So, off it comes, and I take a look at the parts.
And MAN, it's PACKED with parts.

It looks like the thing listens on a CAN bus, and updates the
displays.

Inside, I found the following:
- A Motorola MC68HC908AZ60 micro controller with CAN interface.
- Philips PCF8576CF LCD driver with serial interface.
- Melexis MLX10407 5-channel gauge driver

I didn't look for the 6 light bulb drivers.

So, I'm guessing that the HC908 listens to the CAN bus, and
talks to the LCD driver and the gauge driver to get things
displayed.

So, here we go...

1) I don't need or want the air temperature display.
2) I would like a simple row-of-leds type tachometer display
3) I would like 6 LEDs for the indicator lights.

Does it seem reasonable that I could actually decode the CAN
messages without documentation? (And without going insane?)

Does it seem reasonable that the car would function with this
guy disconnected? (I'll try it next) Or would I have to leave
it connected, and just stuff it under the dash and tap into the
CAN as a passive listener. Is that even possible on CAN?

Any experience using CAN would be appreciated.

 

I am gonna venture a guess that the cluster is mostly listener-only. Any bidirectional goings-on would probably be for self-testing. The speedo with it's more important warning lights might be a bit different, especially since it had the odo button.

I am a total CAN novice, but I am trying to find out more about the inner workings.

 

These guys were working on the Audi CAN bus and trying to use the LED display for various functions such as boost pressure, V-1 display...:

http://www.tripcomp.com/forums/
Maybe they might have some useful knowledge for you.

Good luck!

 

Well, I answered one of my own questions.

The car runs just fine without the tach cluster.

Here is what I'm looking at:

 

Since you are not afraid of this electronics why don’t you use the can bus decoder you have. I.e. mount the PCB of the Tacho some were in the dash and then tap off the IC outputs you need for your own display.

How about some thing like this :smile:

 

Tapping into the current PCB is the easiest way to go, and I'm reserving it
as a last resort since I'd like to be able to reinstall the stock tach if I
ever sell the car and the buyer wants it.

I know I can undo the mods, but HEY, this is an opportunity to learn
CAN which I have never done before, so I'll try the build-it-all
route before I give up and just tap into the tach.

I like the looks of the cluster you posted, and I want to go even shorter.

I'm thinking a curved tach bar like that, and just 5 LEDs below it:
- Brights, blinker, check-engine, airbag and e-brake.

A buddy of mine has a laser-cutter that can cut shapes out of plastic,
and can cut letters and words part-way through, so I can make up a
nide panel, and mount everything to the back.

That would make for a clean-looking dash.

 

Have your thought about a second hand tacho, that should keep the cost down. But if you really want to learn about CAN have a seach on the web, tons for great web sites and keep in touch as i would love to see how your project turns out.