Hi All,

I intend to design an 89c52 based industrial controller. I have following queries about the design.

-- I intend to use SMPS power supply to derive + 5 v dc for processor and + / - 12 v dc for peripherals and relays etc. Should the ground of the processor be isolated from the ground of the peripherals power supply?. What abnomalities may result in the working of the device if the ground is kept common for both?

-- If I go for isolated gnd design for this device, for input / output I may need to use opo-isolator. Are there any octal opo-isolator chips avialable so that I may not need to go for eight different opto-isolator of 4N-35 type? If not octal, can I have referance of more than one pair of opto-isolators?

-- Can any experienced designer suggest good and reliable power supply designs with or without pwm control ICs?

-- My designs in past have shown that when there is heavy mains switching with contactors or high current devices like induction motors switching on and off, the controller misbehaves. Can this have some thing to do with bad power supply designs?

Thanks a lot

Mahesh Vyas.

-- And yes, I also intend to design EPABX system based on 89c52 controller for up to 16 lines. Can I have any suggestion of reference designs and theory involved ?

MV.