Digital Dash

[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