From what i understand the transmission will send out the VSS signal by either a cable or an electronic module
this then is interpreted by the ECM and will then be sent to the speedometer....

Background
350 TBI 5.7L 7747 engine

is there a way to intercept (parallel) the VSS pulses and process it thru a serial cable and display speed /odometer reading thru a laptop

i have a car pc and would love to be able to log my miles digitally. does a program or a possibility of one exist?

 

Most likely something will work. Someplace along the line the VSS pulses become digital. It is the digital signal that is fed to the ECM. 350 TBI w/7747, I'd say the VSS is an optical unit in the dash. A lime green colored box converts the signal to digital where it is fed to the ECM. At this point it is a 0 to 12 volt signal.

Two ways to get it into the laptop: serial port or parallel port. Then have a simple program on the laptop monitor that input and count the pulses: 2000 pulses per mile traveled. The serial port may reconize the +12 v signal on an input such as DTR (or CTS, DSR, which ever is an input).

A voltage divider and input the parallel port can also be done.

RBob.

 

the other thing i thought about doing was tapping into the feed going directly to the speedometer needle in the dash. is that read on resistance or voltage. if its a linear signal 0MPH=0v and 140MPH=12v the conversiong should be like eating pie anyone know what the ecm sends to the speedo needle

 

forgive my ignorance in the earlier post i now know that the vss buffer sends out the signal to the gagues

my only remaining question is how is it ran (signal wise)



tranny > buffer> ecm > gague
analog - analog - digital - digital
ohms? - ohms? - volts? - volts?

Rbob your the ECM mastermind what is the ecm getting to create the values for speed (7747 of course)