BS2SX resets while operating a solenoid

bsc

I have my BS2SX I/O pin going through a 1K resistor to the base of a 2N2222 transistor. The emitter is going to ground and the collector is going to one side of a relay coil. The other side of the relay coil is going to 5 volts DC and I have a 1N4003 diode across the coil. The relay is from Radio Shack. It is part# 275-240, SPDT, 5VDC Coil, nominal current 89.3 mA, and is rated for 1A at 120VAC or 24VDC. The solenoid it is attached to is 12 volts DC and draws a maximum or .75 Amps. When I run my program, the pin goes high and activates the relay and solenoid just fine. When the pin goes low, my stamp appears to reset and it goes back to the begining of my program. I have taken the solenoid out of the picture and the program runs fine operating the relay alone. I'm assuming the solenoid is drawing to much current but I don't fully understand the problem or have a solution. Any help would be appreciated.

Thanks

Mike Green

It sounds like the Stamp is resetting when the relay is turned off. It could be a problem with your program. It could be back-EMF getting into the 5V power supply despite the diode across the relay coil. It is possible the relay is drawing too much current except that you say the relay closes just fine and the Stamp appears to reset when the relay is deactivated.

Some things to try:
1) Add additional filtering to the power supply. You might put a 470uF or 1000uF 6V electrolytic capacitor across the 5V power supply. You could also add a 0.1uF ceramic (50V) capacitor across the 5V supply at the same point.

2) Try using a separate 5V supply for the relay for testing purposes.

3) Make sure the relay's load (the 12V circuit) is separate from the 5V supply for the Stamp.

bsc

Mike

Thanks for responding. I will give your suggestions a try and let you know if they fix the problem.