limiting line voltage...Optocoupler vs Zeiner...suggestions?

[freakn3d]

Howdy all.

I have a working project that has two circuits on sepearte boards, there is a cable between the two that provides power and signal from the parent circuit to the daughter circuit (signal is one way, not bi-directional).

A small micropocessor is sending out a 1k-10kHz variable frequency from the parent circuit to the daughter circuit with 1.7 v pulses.

Problem: occasionally over voltage (two other occasions it was 12v one occasion was that or static) goes up the signal wire and fries the output on the processor. This is bad! (not to mention expensive!)

I have thought of adding a 2.4v (lowest i could find) Zeiner/Resistor combo to the parent circuit to prevent feeding too much voltage to the processor.

Alternately I could use an optocoupler to completely isolate this cable from the processor (i have bread boarded a couple of 4N30 circuits and testing has NOT been sucessful.

What do you think?

[Ldanielrosa]

The zener approach sounds simpler and less expensive. Have you considered using an LED for the voltage limiter? One of the older die-type (not the newer film-type, they have higher voltage cost more and are less forgiving of static) in green will limit to 1.6-2.0V, depending on the current and the manufacturer. It won't take much more space and is likely to be much cheaper than a proper zener diode.

[trigger]

I think is zener cannot handle the sudden goes up voltage and may fired the zener diode.

I prefer to use opto-coupler as it totally isolated the high voltage part from your microprocessor.

[freakn3d]

Ldanielrosa - I hadn't considered using a LED...that's an interesting thought. I'm not familar with the differences between the LEDs as you reffer to them. However I will say that a LED is not as likely to be used since I already have the zeiners in stock. ;)

Trigger - Humm....sudden up voltage as in suddently being dumped with 12v or static type of voltages?

I would also prefer to use an optocoupler but had ZERO sucess in setting up a test circuit (using a 4N30). Have you sucessfully used optocouplers your self?