AVR-Chat

On Thursday, Mar 11, 2004, at 09:32 US/Eastern, Kathy Quinlan wrote:
>> From: John Johnson [mailto:johnatl@mac.com]
>> Hello!
>
> Welcome to our list.

>> I have two designs that use an AVR. One is a garage door
>> manager, using
>> a 2313, keypad, dip relay driven by a transistor. On occasion
>> it would
>> just "go nuts." The door would start going up-down-up-down at
>> about the
>> speed you read that.


> We need more information, like a schematic, but a few common problems:

Working on the schematic. It's built on proto board with point to 
point, however,
I'm going to mill a PC board for it and move all the parts to it.
> Do you have a reverse diode across the relay coil ?
yes
> Do you have a snubber network across the relay contacts ?
no, what do you recommend? 10ohm and 10nf in series? I couldn't find a 
good
web resource, so I'm kind of guessing.

> Do you have a ground plane on the PCB ?
On the board I'm designing, I'm going to surround the relay area with a 
pour
(I think it's called). Maybe I could upload a pic of the design for 
critique?

> Are the supplies isolated between the AVR and the relay ?
On the garage door minder, no. The relay is a 5v reed unit, the AVR 
pulls
one leg of the coil to ground to turn it on.

> A solidstate relay would solve some of the problems. Or a triac and 
> zero
> crossing opto coupler.
>

> They are quite the oposite, very reliable if you treat them with 
> respect
> (IE no over voltage) and follow good design practices (I will write an
> appnote one day and put on my website, as this is a common problem)
>

Thanks again Kat. It's good to hear they are reliable. I kind of thought
they would be, and that, surely it is me.

It would be nice if Atmel had some reference design boards on their
site (like the Butterfly). I guess the applications vary so widely that 
that is virtually
impossible.


Regards,
   JJ