Buffer suggestion needed

Erik Friesen

I am wanting to interface my prop to a ac waveform ranging from .5v to 35v and up to 128,000hz. (ABS signal from vehicle).· Some have suggested optocouplers to me in the past.· I don't know what the drive capabilities of auto computers are and I am a little unsure as I don't want to damage the computer.· Would a schmitt·buffer with an inline resistor do the trick?· Or do I need to use a transistor to prebuffer the signal?(and invert it)

Mike Green

We need more information about the signal. You probably should use an optocoupler, possibly with a transistor buffer and some kind of signal conditioning at the input (like a series resistor, maybe a clipping diode for the negative half of the signal).

Erik Friesen

This signal is coming from a magnetic pickup off the wheel. It varies in speed with the speed of the vehicle. At low speeds it is about 500mv. The signal is up to 5000hz, not 128,000 as I said previously. It is a sine wave that I obviously want to convert to a square wave.A typical optocoupler needs up to 60ma to drive it I believe. This isn't too much drag on the vehicle components?

Mike Green

Here's an example of an optocoupler that needs only 1.6ma (www.fairchildsemi.com/ds/FO/FOD2200.pdf).

Erik Friesen

I guess that shows I don't know where to look. Is that available from Mouser?

Ariba

With 500mV you can't drive an optocouplers led. Are this 500mV peak to peak or measured with a multimeter?
What is the minimal frequency that should be recognized?

Phil Pilgrim (PhiPi)

You could use the output of a comparator to drive the optocoupler. The LT1017, for example, can be powered from up to 40VDC and will accept your 35V input. By adding some feedback, you can get a little hysteresis for stability. You do need to ascertain that a common threshold will work for all input voltages, though.

-Phil