Com_VC

Hi all,

Just wondering if there was some way available to get a serial data speedo from a newer car working in a carby vehicle?

Thanks

JMatlock88

Yes, the mid-year TPI vehicles have an independent signal-conditioning box called a speedometer buffer. It is a yellow box located under the passenger side dash of TPI/TBI cars on the order of 1986-1989. This box consists of power, ground, low reference signal in from VSS, high reference signal in from VSS, and two output pairs. The outputs condition the signal for electric speedometer input and cruise control input. Late models have this signal conditioning built into the ECM. You need this box or an equivelent dakota digital box in order to properly run an 86-92 electric speedo. Or you can eliminate the box alltogether by using an aftermarket speedometer such as autometer. In this case, you simply feed the VSS high and low signal directly to the gage and it has a built-in calibration multiplier that you can set up for for any VSS and rear gear.

Com_VC

Thanks for the quick reply. Any idea where I may find one of these? I'm from Australia so seeing one of these here is very rare, not sure how common they are over there? I'm guessing i'd have to have one sent over.

JMatlock88

Wait, I'm not sure I interpreted your question correctly. Are you talking about a NEW (non-thirdgen) vehicle speedometer driven by onboard BUS systems?

JMatlock88

Thirdgen speedometers and buffer boxes are extremely common here in the US. I'm sure you won't have much problem locating one here and having it shipped to you.

Com_VC

Well the cluster I have here is from an Australian Holden built in 1997. It is made by VDO so I assume it would be pretty much the same technology. I know it uses high and low reference signals and would most likely be driven by a BUS system.

How much would I be looking at for the buffer box?

JMatlock88

Well when we are refering to "BUS" systems, we are usually refering to a digital signal. That is, a digital "packet" is sent out of the ecm to all of the gages and equipment. The gages pick up the portion of this digital stream that pertains to their input needs.

Thirdgen VSS signal (high and reference wire) are an analog signal...sine wave out of the VSS and square wave after the buffer.

You'll need to check for sure on your Holden gage set whether it is digital (BUS) or analog. If it requires a digital signal, then there is really no way to set up the gage in a thirdgen without some custom designed software/hardware.

The buffer boxes, again for analog only, are usually on the order of $150 usd from dealorships and maybe around $free-50 from someone on thirdgen.org.

jlarsson

iTrader: (5)

I got the VSS buffer (yellow box) send me a PM

Cheers

Com_VC

I found out that it uses serial data.

So is there a convertor available to convert from RS232 - high and low reference signals?

Thanks

JMatlock88

Not that I'm aware. You'd have to make your own custom hardware like I said or use the entire system from the other car.

MrDude_1

if you're willing to learn how to program PIC microcontrollers (or any other microcontroller) you could easily write a program to take the VSS signal in, and put standard serial out..... you just need to know the details of what the cluster expects.... id suspect that it takes commands almost identical to that of 4thgen Fbodys, and thats documented online.

JMatlock88

Agreed. A little C programming and a $5 PIC Microcontroller will do the trick. I have a few lying around.

Is this type of thing something that's commonly requested?

MrDude, which 4th gen years and gages use serial data? If this is the case, how have the other guys been doing the 4th gen dash swap?

JMatlock88

The '99+ 4th gen dash has one sending unit for oil pressure, that's it. The rest are fed serial data.

MrDude_1

yup.

thats also why the 4thgen dragrace guys like their aftermarket tachs and shiftlights...

the engine can rev so fast that its bouncing off the rev limiter before the tach reads that high.


but its fast enough for everything short of drag racing.

Com_VC

Hi,

I found this diagram on the cluster I have here. Do you think I could use the buffer box? Basically all I care about is the speedometer working and hopefully odometer.

Also found this little bit of information.

“Once the PCM has calculated the vehicle speed it then pulses circuit 123 (Violet/White wire) to earth, this will cause the 12 volts at terminal 17 of the instruments to be pulled down to less than 0.2 volts. The instrument determines the vehicle speed and the kilometres from the numbers of pulses it receives. The PCM also transmits vehicle speed information to other control modules via the serial data bus normal mode message.”

Thanks