Digital Dash

[superli]

Ivan141 Wrote:Changing resistor values on the stock RPM input IC is a bit of dark magic sadly. It is pretty much impossible to find a datasheet for it, it is nowhere to be found online, and the manufacturer refuses to look for/provide a datasheet for an obsolete IC.
Without that data you dont really know what you are doing when swapping parts. Trial an error is a possibility though.

I will try to follow the signal, and understand how it is treated.
Maybe I'll succeed, maybe not... but I will do my best and some persons around me are very good in electronic it helps.

Ivan141 Wrote:There is another topic on this subject where I dumped about all usefull links I could find on the subject.

I didn't find it...

[Ivan141]

Hmm.. cant find it myself either. Dunno where I put all that stuff then.

Anyway, have a look at the following threads to know what needs changing:
http://www.toymods.org.au/forums/tech-co...utput.html
http://www.autosoftsys.com/supra/tachcompare/





Basically you have an R/C circuit where 3 resistors and a capacitor are, the resistors vary for different car models (R/C circuits have an exact discharge time that I suspect is important for the RPM calibration).

Then there is a resistor inline with the input signal. Something tells me this one is important for the input level of the rpm signal. If you take a look at the last link, you'll notice the 1JZ&7MGTE use 15k whilst a 7MGE uses 30k.
The turbo engines both have coil packs and probably don't use the coil- signal for input, whereas the 7MGE is a distributor driven car like the AE86, and has a higher resistor value for more attenuation.

The last resistor thats different between the above mentioned engines is R8, which is on a voltage supply input. No idea what it does, but I suspect it is related to the input detection as well. This one is lower for the 7MGE, so perhaps a higher voltage value is used for comparing the input signal? Without a datasheet it is hard to tell, but a bit of experimentation with some potentiometers in the correct value ranges could probably reveal all you need to know.

Comparison of tach components
# 7M-GE (1987) 7M-GTE (198 1JZ-GTE (1992)
R1 62K 130K 100K
R2 12K 12K 12K
R3 510 560 560
R4 30K 15K 15K
R5 55 55 55
R6 15 15 15
R7 560 560 560
R8 33K 39K 39K
R9 47 47 47
C1 ?? 0.1+ 35F 0.1+ 35F
C2 ?? 472 50K NCC 472 50K NCC
C3 47uF 10V 47uF 10V 47uF 10V
C4 ?? 33uF 25V 33uF 25V
IC1 ?? Toshiba 8806K T2685A Toshiba 9214K T2685A

[superli]

thank you very much for all these informations.
It will help me.
Tomorrow I will seach if there is the T2586A in the digidash.

[Ivan141]

I'm afraid you'll only find that IC in analog dashboards.. it's a needle driver IC, the digidash doesnt have needles.
What you'll need to do is follow the tach input signal and see if there are any resistors inline with it. My expectation is that it wont be as easy to swap components as on an analog dash, but you never know.
Easiest thing to do is build yourself a signal booster to emulate a coil- signal. There is plenty of info available on that topic. I also build them for people from time to time, but circumstances at home dont allow for this at the moment.

[rongfk]

http://club4ag.com/forums/viewtopic.php?f=15&t=5119

[choyr]

hi ivan,

i used the diagram pic you posted, and unluckily, my rpm still doesn't work. I check the tach signal and it is working. I don't know if there is a missing +12V to it

[Ivan141]

Cant help you much there.. I don't own a digidash, I have only had one leant to me by Aram in order to figure out the wiring. I was planning to try to get it running on my desk to prove a point, but life got in the way of all my plans this year so I returned him his dash.

The diagram I posted is not my own, it is my translation of a Japanese diagram I found of a guy there who managed to convert his dash successfully, and then adapted to the European connector wiring.
I'd say make sure you got all the grounds and 12v supplies working and then check the tach further.

Are you using the original tach signal (coil negative)?

[choyr]

i connected the +12v to the pin 1 and 9 of left plug, and the ground to pin 2 of left plug and pin 8 of right plug, connected tach signal (-) to pin 11 of left plug, and water temperature sender (-) to pin 7 of left plug. this japanese diagram is the same with the excel file uploaded here, just that i noticed the water temperature sender is different pin but same wire color (maybe some typo).

i also uploaded the video to share what i have done.

http://youtu.be/OWGWSznHaRM

as you see, the tester reads Hz and it increases if i rev the engine, but the rpm doesn't move. also, notice the temperature is not changing, but i checked the resistance and it varies depending on the temp.

it's hard to determine it is hardware fault, i have no spare to check, but when i use the analog cluster, it works.

4age 20v / ke70

[george delorean]

To Choyr: you must simulated fuelsender!!! Then you will work tachometer.
See schematic diagram!

[Ivan141]

If that is correct then it is very usefull info to have on this page, thanks!