wiring and signal strength query

[hardsteppa]

good day old chums

so, if like me,  you're running a few accessories like EBC, datalogger, knocklight, AFC, they will need tapping into signals like rpm and throttle, etc, off the ecu. Query is, if you run multiple taps into the ecu's rpm wire for example, does the signal strength weaken as it's run off to multiple sources, or will the ecu wire and all associated devices get a full strength signal? 

thank u

[GTSBoy]

Nah.  Typical 5V signal working against the seriously high input impedance of any decent device that wants to look at that signal will flow a poofteenth of f**k all current.  if some arsehat is responsible for the design of the input on the device, however, and it sinks a reasonable amount of current, then all bets are off.

[hardsteppa]

Thanks gtsb

[zoomzoom]

Yes, connecting piggyback devices to sensors can cause a voltage drop on the measured device. I had this issue with analogue signals like TPS etc. Digital signals are not going to be affected in the same way however, as long as they meet their threshold voltages.

You shouldn't assume that the analogue inputs will be "high impedance", in fact you would expect lower impedance inputs because they provide greater immunity against induced voltages, thereby reducing noise on your signal. For example my adaptronic ECU lists some of the input impedances as 20k. I would consider "high impedance" to be greater than 1M ohm.

Ideally, you'd also like to know the source impedance of the 5v sensor reference, not to mention any resistances in the 20 year old wiring. If you can calibrate any device which is measuring a voltage, it doesn't matter too much anyways.