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Subject: Re: How do i measure signals without affecting them ?
Date: Wed, 20 Nov 2002 08:30:07 GMT
NNTP-Posting-Date: Wed, 20 Nov 2002 03:30:07 EST
Organization: Road Runner
> I want to measure the pulses from various devices, all of which put out some
> sort of pulse. Ie, hall effect device that has already been conditioned to
> be a square wave.
> How would i interface a PIC with the same wire the sensors main signal is on
> without affecting the signal ?
> I have been told i can use a rather large resistor (in the megaohms) in
> conjunction with a schmitt trigger to do it cleanly, but i dont quite
> understand how the voltage going through the resistor would be enough to
> activate the schmitt?
> If anyone knows of some ways to do this please post them.
> Also, what is the formal name for this type of interfacing so i can do a
> proper search for more info ?
OK. Now that you have clarified what you want to do, I would recommend
using the interface that the vehicle already has. There are cables that
can hook to the vehicles "brains" to interface with a laptop. Using
software, the signals from the cable give you all the diagnostic info.
There is no need to tap directly onto the sensors. I'm sure a search on
google will turn up some diagrams and software. Once you have the
interface cable, you should be able to connect whatever you want to the
lines as long as it is some logic level input.