AVR-Chat

On Aug 11, 2004, at 9:07 PM, 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.)

The series resistor on the relay may not provide enough current for the 
relay to operate.  Use an external transistor if you need more current 
than the microcontroller output is rated for. Also put a small diode 
across the relay coil in the opposite direction than you would expect, 
i.e. cathode to +5V and anode to the 150 ohm resistor side.  Without 
the diode, the back-EMF from the relay coil will produce a high voltage 
pulse directly into the micro.


Mike W4LNA