Relay circuit causing feedback and stamp reset
I'm working on a mechanical clock project which, among other things, rings a standard household bell chime at the top of every hour (up to 12 times in sequence, with a gap of a few seconds between each chime). The problem is that after 5-7 chimes, I'm getting the dreaded feedback through the circuit which then hangs the Stamp. My circuit looks fine (it's identical to the "reference" circuit posted on this forum) - do you know where I might be going wrong?
Here are the specifics...
Again, I know the circuit works... it's just that after around 5 to 7 chimes the stamp freezes.
Thanks for any advice!
Here are the specifics...
- The resistor between the Stamp Pin and the transistor is a 10k, 1/4 watt (have also tried a lower 330 ohm)
- The NPN transistor is a standard "pn2222" from Jameco
- I use a 1N4001 diode as shown in the schematic
- The relay is an Omron G5LE from Jameco. It's rated at supporting a load of·10amp @ 250vAC
- The power for the chime is a standard household bell transformer: 16V AC @ 10VA (note: AC, not DC)
- The relay effectively completes the circuit between the transformer and the door bell. The code keeps the relay on for about 1/4 of a second before releasing it, then waits 3 seconds before it chimes again.
Again, I know the circuit works... it's just that after around 5 to 7 chimes the stamp freezes.
Thanks for any advice!
bmp
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225K
Comments
Also, is the diode OK? You might also benefit from a 0.1 uF cap between +5 and Vss very close to the stamp.
If the RESET connection on the stamp were physically close to the relay or the chime, you could possibly have enough pickup to reset the stamp. I think you can pull-up the reset line with a 15K resistor to make it a bit more robust, if this turns out to be the problem.
Tell us more about the relay/stamp DC power.
Cheers
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Tom Sisk
http://www.siskconsult.com
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So, I think, problem solved. Thank you.
EDIT: Saw your reply...So you may have it solved, but good future debugging advice.·
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Chris Savage
Parallax Tech Support