Gorund Loop

You will have to connect the grounds otherwise one board will have no ground ref to the other, and it won't work since the wall supply would be a floating ground, driving a logic input into such a setup will probably cause damage. You wall plug ground could float up by 100's of volts so you have to connect the grounds together.

HTH, Chris

Hello,

Thanks for ur reply! What about using Analog isolation beteween the two boards?

Regards John

Why do you need to isolate them anyway ? I run my logic circuits off 2 or 3 seperate wall plug supplies and never had any troubles. The only time you would really need isolation is when driving mains equipment such as lamps etc from PC driven logic interfaces, then if the lamp drive fails it won't take out the logic board with it..

Chris

Is that a double insulated mains adaptor with no earth pin or ?

Hello,

Please look for the regulated table tops power supply in the following link

Thanks Regards John

CWatters wrote:

Yes looks like there probably is a connection between mains earth pin and the screen. Anyway even if you used one without an earth you can still have "loop" type problems. I have had problems with mains transients (spikes) coupling into just such a loop. The two items of equipment worked fine until you connected them together. Are you just building one for an experiment or is this a product that's going to be mass produced? Any chance you can insert some opto isolators somewhere?

Hello,

Thank you for ur reply! I did not understand what do you mean by earth pin and the screen? yes, I am building it as a prototype. I thought of using Analog optoisolators but I found that working with them is not so easy. The specifications of analog signal coming from my computer board is as follows:

1. maximum amplitude : plus minus 10volts ( max ) plus minus 0.1 ( min)

1. frequency: 1Mhz to 10Mhz.( max ) 0.1 Hz ( min)

Regards John

CWatters wrote:

I mean that the earth pin on the plug is probably connected to the screen of the DIN connector if you have one with tha option. That's as well as the COM/0V.

Does the card in the PC provide any power rails? Could you power the analog part of your circuit from that then pass digital signals through opto isolators?