Hi,

I am currnetly working on PIC microcontroller based automated meters. I am using PIC16F76 (SOIC) to display values on 7-seg display units, 6 numbers, 5Volts, Common cathode. I have two issues.

1. The display unit is at 2 metres approx from the PIC board. I use ULN in PIC board, which is used to ground the 7-seg common cathode pins. The PORTB of PIC is directly used to connect the data pins of 7-seg. Can I connect the PORT pins of PIC to directly connect 7-seg load placed at 2 meters? Will it cause any issue? Or should there be a driver (transistor) at the microcontroller end for 7-seg anode nodes also? Recently I got my PIC IC suddently got burnt off, though it was working fine initially for 15 days. Any inputs please...

2. I have 220-15V 1amp transformer placed close to PIC board, supplying power to the board. Will it cause any issue through EMI or something? Is it safe to have the transformer close to PIC board?

Divakar Raj. R

 

Hard to say anyrhing without a schematic.

 

EMI is finicky. It may be present at times and not at others, it may have a special day of the month it likes to flare up

Best bet with EMI is to design for the worst case and pray for the best. In other words- don't tempt it with designs that can be affected by it, even if you don't appear to have a problem with it. The problems can occur later in strange ways.

As for drivers, they also are recommended. The 'strange' death of your micro points to such an issue as isolation between the micro and the display. Suggested that you use a driver, if only for isolation, between your micro and your display.