AVR-Chat

At 09:07 PM 8/11/2004, kc9dag wrote:

>I have designed a circuit that works fine when I run it on the 
>STK500, but when I tried to move the circuit to its own board (this 
>is the first time I have done an avr w/o using the STK500) it does 
>not work.  I was wondering if someone would mind looking at the 
>schematic (http://www.dpicts.com/Tiny15L-LaserDetector.jpg) and 
>telling me what I am doing wrong?  The circuit basicly waits for a 
>laser beam to be broken (detected by the photodiode) and then 
>activates a relay in a set time pattern.  When I try the soldered 
>circuit, the relay never activates regardless of the laser (again it 
>worked fine when it was hooked up to the stk500, only using an led 
>instead of the relay.)

Relay activation current is too high. 
Relays don't usually have a pull-in current of a few mA. Them that do, are LARGE, and PRICEY.

You also have no suppression diode across the coil, so when you turn the coil off, you'll stand a good chance of frying the tiny.

Add an NPN transistor. E to ground, C to the relay coil, B to the tiny, through a 1k resistor.  Add a 10k resistor from the tiny's output pin to ground. 
Add a diode across the relay coil, so that the diode does not conduct when the transistor is on.