| ??? 04/22/10 14:11 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#175274 - Two major mistakes... Responding to: ???'s previous message |
Manish said:
The false triggering events happen when we toggle any relay in the system though each of them has a snubber installed nearby (R=47 ohms C=100n) I even observed that the last key pressed was getting repeated Which is quite normal, when you omit any shielding and do not have a solid ground plane. Manish said:
The 100n caps are at i/ps pins only but in my keypad routine I cycle a high I a nibble So should I remove from there ? Yes, these are the outputs that are short circuited by the caps. Manish said:
One question here as you see in my images the 16 o/p of ULN2803 are wired to realy board and a common +12v is separately wired does this make a problem (current loop ) if yes what can be possible solution for this to take parallel wires for 12v and gnd together or any other? If the 12V isn't used elsewhere you can feed it separately to the board, provided, that supply line and ground return line are routed closest to another. Manish said:
The pcb and assembly photos are uploaded on the web on following link You make two major mistakes on the micro's pcb: 1. You urgently need a solid ground plane, which means that you must have at least an intelligently routed double sided board or a standard 4-layer board. 2. You must not connect the many cables at different locations on the pcb, because any interference running from one cable to another must then run across the whole pcb!!!!!!!!!! Route the layout in such a way, that all cables leave the board at only "one" place! At this place mount all the filtering too. To this place connect all the cable shields. If you use a metallic enclosure connect it to this place. The ground at this place is dirty, so put the micro's circuitry not too close to this place. Kai Klaas |
