Sensor ground question

[Twinspark]

Hi

my car uses a 12v square wave pulse for vehicle speed. Can i simply connect this signal to the MS3x (PT4) in parallel with the speedo? My concern is that the signal ground will not be at MS but at another point somewhere on the chassis.

cheers,

Matt

[grom_e30]

i think pt4 is only good for 5v signals.

[Twinspark]

THanks Grom for picking that up! I haven't determined the frequency of the pulses so went with PT4 for its high frequency capability.

SO an optocoupler would solve both the voltage and the grounding issues. Or should i just connect the speedometer signal to say nitrous in?

[Twinspark]

can the tach opto in circuit be re-purposed for a 12v pulsed input? my build uses VR for tach in. Also, at what hz do the inputs 'Datalog in', 'Tableswitch in', 'Launch in' stop working? Factory VSS is 700hz at 200km/hr.

[DaveEFI]

Using the opto input seems a very sensible route. If you look at the old MS1 instructions, you should find a suitable configuration for your signal, if it's not in your manual.