Remote "Back Window" MPG Display?

Fred Kaluza · 08-27-2004, 07:32 AM

Has anyone been able to extract segment driver information from the dash MPG display and been able to fabricate a nice bright large display for MPG so drivers behind me can see how I'm doing? Are their any remote MPG display kits being marketed? I think that alone would be responsible for for increase in Insight interest as much as anything else. Fred in Michigan.

Holicow · 08-27-2004, 09:10 AM

This was brought up recently, but I can't find the thread. There are no kits available, that I know of. I would love to have one.

It seems we are at the mercy of someone who knows more about car electricals than I.

james · 08-27-2004, 05:31 PM

I haven't done it, but from the wiring diagrams in the manual, it looks as though all the info that's displayed on the dash is being sent over a pair of wires, using some sort of serial protocol. So if you had access to a recording scope or something of that sort, it should be pretty easy to decode. Then if you tap in to those lines, you could use them to drive any sort of display.

Resist · 08-27-2004, 08:19 PM

I have already seen LED moving message sign type of plate frames on cars. I can't find information about them though. Now if only someont could tie that into the instant mpg indicator.

ext1jdh · 08-28-2004, 12:12 AM

I know the plate frames use standard 9 pin serial that you plug into a PC. It should be pretty simple to throw it together but I have neither the time nor the inclination to tear my dash apart

08-30-2004, 11:59 AM

Quote:

Originally Posted by ext1jdh

It should be pretty simple to throw it together but I have neither the time nor the inclination to tear my dash apart

It is more complicated than it seems on the surface. First you have to reverse engineer the protocol used to send the information to the dash display and extract only the information desired. Then you have to encapsulate that data in a different protocol (RS 232 serial?) and send it to the second display. The savvy electrical engineer could probably build a PIC microcontroller circuit to do the decode/encode, but deciphering the signal in the first place is no small task. Anybody have a recording O-scope handy?

Fred Kaluza · 08-30-2004, 11:26 PM

Well, OK, I don't have a scope that records anything and I also don't feel like tearing the dash apart.....yet. But, if we decode the data stream, then we still need to create a "smart" rear display. One that has enough brains in it to decode and display just the same as the one in the dash. I'm proposing a "dumb" display. I'm not sure how may segments are in the dash mounted unit or of the segents present, just how many are being used. But, assuming it's seven per digit, then maybe a ribbon cable with 3x7 plus hot & ground equals 23 leads running from front to rear. It's probably simpler to splice into the driver outputs anyway. I admit using one of those pre-made scrolling displays would be really cool since theoretically you could send other text. Still thinking here. Thanks for the ideas. Fred in Warren, MI.

Yves M. · 08-31-2004, 08:29 AM

I agree with Fred. It must be simpler to connect to the display itself. And then those leads could be used through transistors, to power up a bigger display.

james · 08-31-2004, 02:54 PM

I don't think you'd have to tear the dash apart. Everything comes out of the same processing unit, which if I remember correctly is mounted under the dash on the passenger side, and fairly accessable. Should be the same one that the diagnostic connector goes to.

Getting to the display is (according to the shop manual - I haven't actually done it) a major PITA. Pull the airbag, drop the steering column...

Armin · 09-01-2004, 08:29 AM

Quote:

Originally Posted by Fred Kaluza

assuming it's seven per digit, then maybe a ribbon cable with 3x7 plus hot & ground equals 23 leads running from front to rear. It's probably simpler to splice into the driver outputs anyway.

Fred,

I don't think it will be that easy! The dash display is LCD, and judging by the total number of segments, it must be highly multiplexed.

First, it will be very difficult to tap any of the signals, since the wire capacity or the load of any circuit you hook up to them will dampen the original signal and screw up your dash display. LCD drivers are not made to really "drive" any load.

Secondly, even if you use some low capacity, high impedance buffers to recover the signals without harm, you now need to demux the LCD drive signals to figure out which segments are lit. It's doable, but by this time it's probably easier to reverse-engineer the communication protocol.