AVR-Chat

> -----Original Message-----
> From: John Johnson [mailto:johnatl@mac.com] 
> Sent: Thursday, 11 March 2004 8:59 PM
> To: AVR-Chat@yahoogroups.com
> Subject: [AVR-Chat] Hello and EMI/RFI
> 
> 
> Hello!

Welcome to our list.
 
> I'm JJ, AVR, electronics, machinist type person. It's good to find a 
> resource for AVR folks.
> 
> 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:

Do you have a reverse diode across the relay coil ?
Do you have a snubber network across the relay contacts ?
Do you have a ground plane on the PCB ?
Are the supplies isolated between the AVR and the relay ?

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

 
> The other is a heater controller. It uses an 8535 to read an 
> LM74(37?) 
> temperature device, and turn a space heater on and off. It 
> uses a hiigh 
> current mechanical relay driven by a transistor that is driven by an 
> optoisolator (4N22?). It has the same problem as the garage door 
> control. Sometimes, it gets spastic, turning the relay 
> on-off-on-bzzt-off-bzzt, etc.

Same as above ;o)

> 
> I use the normal resistor to Vcc, cap to Gnd on the reset line, along 
> with bypass caps (100nf) close to the ICs. I guess I'm missing 
> something. Any suggestions? I really like the AVR, and am trying to 
> convince myself it something I've done, so I won't think they're 
> unreliable.

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!
> 
> Regards,
>    JJ

Regards,

Kat (list mom) 

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.618 / Virus Database: 397 - Release Date: 9/03/2004