digital project, recomendations? help?

[MKII_Tuner]

ok im wanting to do a digital guage converter?
on my speedometer, im not actually knowledged in this department,
so im sorry if this is a really easy question to answer

but i have a 92 5sfe
and really considering doing a v6 swap..
so not sure if its best to wait for this project
but i want to put a digital guage up as my speedometer
and later rearrange my guages with some custom guages

and work on custom dash and interior

[CJMR2T]

Im in the middle of the same thing (sorta) not going with digital though, just a better / more accurate set of custom gauges in the dash. Mine will still be anolog though, just a better units and on oil pressure guage in place of the factory boost gauge.

As for the digital, there are a few companies that make digital units that are programmable to work with any car that has a electronic VSS (vehical speed sensor). You can tap off of the you can tap off of the electronic sensor output for the cruise control if you have cruise control on your car or convert over to the >93 full electronic VSS. The only problem with either is the VSS signal to the ECU and PS system if you have PS as the out signal to these are generated by the speedo head unit.

What Im trying to figure out is how the >93 electronic speedo buffers the signal from the VSS. Looking at the wiring, the VSS sends the signal to the Speedo head unit, then the head unit outputs a signal to the different units that need need a speed signal input. My asumption is that the input and output signals are different or toyota wouldn't have ran a wire from the engine harness all that way to the speedo then another wire from the speedo back to the ecu when they could have just "T'ed" to both the ECU and the speedo head unit.... The only thing I can think of is it changes the digital pulse count from what the VSS outputs but this doesn't make sense as every toyota I've ever delt with is calibrated to 4000 pulse per mile (IIRC) for both the ECU's (be it the engine ECU, PS ECU, Cruise ECU, etc..) and the electronic speedo head units.

Back to the digital speedo's, like I said, there are a few companies that make them including Autometer, Cyberdyne, Dakota Digital, etc...

If you have a good understanding of electronics and know how to read circuit diagrams and build circuits and PCB's there are several pages (google search) on how to build a digital speedo.

[MKII_Tuner]

ty i will look into it, im pretty good with electronics, even if they seem confusing, lol

Originally Posted by CJMR2T

Im in the middle of the same thing (sorta) not going with digital though, just a better / more accurate set of custom gauges in the dash. Mine will still be anolog though, just a better units and on oil pressure guage in place of the factory boost gauge.

As for the digital, there are a few companies that make digital units that are programmable to work with any car that has a electronic VSS (vehical speed sensor). You can tap off of the you can tap off of the electronic sensor output for the cruise control if you have cruise control on your car or convert over to the >93 full electronic VSS. The only problem with either is the VSS signal to the ECU and PS system if you have PS as the out signal to these are generated by the speedo head unit.

What Im trying to figure out is how the >93 electronic speedo buffers the signal from the VSS. Looking at the wiring, the VSS sends the signal to the Speedo head unit, then the head unit outputs a signal to the different units that need need a speed signal input. My asumption is that the input and output signals are different or toyota wouldn't have ran a wire from the engine harness all that way to the speedo then another wire from the speedo back to the ecu when they could have just "T'ed" to both the ECU and the speedo head unit.... The only thing I can think of is it changes the digital pulse count from what the VSS outputs but this doesn't make sense as every toyota I've ever delt with is calibrated to 4000 pulse per mile (IIRC) for both the ECU's (be it the engine ECU, PS ECU, Cruise ECU, etc..) and the electronic speedo head units.

Back to the digital speedo's, like I said, there are a few companies that make them including Autometer, Cyberdyne, Dakota Digital, etc...

If you have a good understanding of electronics and know how to read circuit diagrams and build circuits and PCB's there are several pages (google search) on how to build a digital speedo.

[CJMR2T]

I figured out how / why toyota wired it the way it did. A simple NPN transistor will solve the issue with supplying the speed signal to the Engine ECU, PS ECU, and ABS ECU.

Signal from VSS wired to the base of the Transistor
ECU's wired to the collector of the Transistor
and ground to the emitter of the Transistor

with the above, the problem is solved.

[MKII_Tuner]

ty, ill have to remember that when i go into the project.. which will be when i have the time and money

[CJMR2T]

Yeah, the VSS output is a pulsed 12v where the engine uses a pull-up type circuit thus it needs a pulsed ground. The speedo has a read switch built into it and pulses a ground. The later cars that had electronic speedo's did this signal coversion/conditioning within itself.

I do thing thing that the two inputs to the Transistor should be diode protected. (i.e. the VSS to Base should be diode protected and the ECU to collector should also be diode protected.)... I forgot to mention that in the previous post. Probably not fully necessarly, but wont hurt either.

[MKII_Tuner]

im not sure if they will do it, but im considering having digital dakota do a custom digital gauges.. so maybe they will install everything properly.. and i wont have to mess with the confusing wiring of the gauges, but im just gona hope they do

[CJMR2T]

Ok, a small update to my fix for the speed signal issue with converting to the to a digital signal...

The early cable drive speedo's pulse a ground for the Engine ECU and the P/S ECU. The cruise speed sensor does the same thing so there is no need to use a transistor as I said before. Why toyota added the sensor on cruise equiped cars is beyound me. It seems they only did it on Manual trans cars, but not on auto trans cars... Auto trans cars have the cruise speed signal tapped off the speedo head unit along with the other ECU's.... Basically the manual cars with cruise was a redundent adding of wiring and parts....

If you wanted to build a digital speedo using the cruise speed sensor for a manual car, you will need to build it in a way that is its looking for a ground pulse...

93 and later cars use a standard VSS and an electronic speedo. The VSS from these cars output a pulsed 12v signal. If you were to use a VSS, then you would need to use the NPN transistor as I mentioned above...

I built and tested the setup today and the only thing I have to add to what was mentions above is the need to add a 1k Ohm load resistor is needed inline one the base of the collector...


So to summerize the use of a 93 and up VSS (probably easier when doing a digital setup)

VSS signal to 1K ohm resistor to Base of transistor
ECU signal leads to Collector of transistor
Emmitter of transistor to ground