Hi,
I understand there is a risk of voltage spikes finding their way from the power supply to the computer which could cook the PCs internal componants. I have heard talk about a device which uses LEDs and Photo sensitive diodes to form a barrier in the cable between the two. Can anyone shed any light on these devices, how much, where etc.
Thanks
Splint

Hi Splint,

I believe the mystery device is called an optoisolator. If I understand the concept correctly, I believe the circuitry on either side of the optoisolator runs each on its own power supply. This provides the seperation of the voltages. The optoisolator then translates a signal from one circuit system to the next by means of light.

Splint:
One source of optoisolators is http://www.digikey.com
They have a searchable on-line catalog.

robotic regards,

Tom
= = = = =
If a man will begin with certainties, he shall end in doubts, but if he will be content to begin with doubts, he shall end in certainties.
- - Francis Bacon

Hi mate,
Is it a breakout board you are after? If so check out this site, www.campbelldesigns.com

Sorry I dont know how to make a web address linkable/live/dynamic or whatever the correct terminology is.( maybe someone can show me)

Cheers M

Hey look it did it by itself, What does it?, Is it the fact you type in www??

Thanks guys, the optoiscolator was what I was thinking of. The breakout board from Campbel designs looks perfect for what I need.
Garagefela, yes a complete url will turn into an active link, even in other programs like word or excell. Using an @ in text will make an active email address.
Thanks
Splint

Splint, There is also another source of voltage spikes that I have seen cause problems if not taken care of, that is back emf suppression of relays,solenoids, contactors etc, even if optoisolators are used for switching.
For AC devices a resistor/capacitor in series combination is used across the coil, the values depend on the size of the device, also on AC a varistor (voltage dependant resistor) can be used. On DC a diode should be wired across the coil in reverse bias to the DC supply i.e. anode to DC+. The diode will delay the opening slightly of the relay, but this is not usually a problem.
Al

For AC devices a resistor/capacitor in series combination is used across the coil, the values depend on the size of the device, also on AC a varistor (voltage dependant resistor) can be used. On DC a diode should be wired across the coil in reverse bias to the DC supply i.e. anode to DC+. The diode will delay the opening slightly of the relay, but this is not usually a problem.


Or you can use a MOV ( ?Momentarily? Over Voltage) in parelell with the relay. These will pass a voltage that is over its rated value only. ie spikes. They are commponly use as surge protecting devices on computers.

As I mentioned, the MOV (metal oxide varistor) or VDR can be used for suppression, actually they are high resistance at the normal operating voltage and rapidly decrease in resistance as the voltage across them rise, thus offering a load to the voltage surge, on AC some relay manufacturers recommend the R/C method over MOV. Most contactor manuf. supply a tailored R/C suppressor tailored for their devices.
MOV's are more susceptible to destruction than R/C networks and if not discovered, the device no longer has surge suppression.
Al

I knew that, I was just testing. :)