The spector of EMF

chazRoman

I need to trigger two solenoid valves (110V at 8W) on a pneumatic system I'm building.
I have a BASIC stamp outputting +5V to the base of a set of two transistors set up in a Darlington array.
Then I have the Emitter/Collector being the neutral for a SPST relay's coil. (I have a 1N4003 flyback diode across the contacts of the coil)

I think this is very similar to the diagram in Nuts and Volts column 6. However, I have an issue:
When My program reaches the point when it is supposed to continuously alternate between the two solenoids,
it fires the solenoids for about 4 alternations and is then somehow kicked into the beginning of the code again
to my 'WATCHDOG' loop of a blinking LED.

I think I've eliminated everything program-wise that could cause such an issue. Is it possible that,
although I have a flyback diode and Darlington array, that there is some sort of flyback still disrupting the stamp?

Amaral

possible it is , but very unlikely. if it happens your stamp would probably by gone !

check your code for a MISSING "RETURN" or "GOTO" that ends in a dead routine. that can be the reason for reset.


Hope to help
Amaral

MSDTech

Check your power supply. Sounds like the low voltage monitor is restarting the stamp.

Beau Schwabe

chazRoman,
·
What happens if you place an external 1K resistor across the ATN and VSS?
·
Many years ago, I made an industrial blower/vacuum system (240VAC) controller that had similar problems.· but I had left a custom very long
30 foot programming cable connected to the unit that acted like an antenna.
·
Placing a resistor across the ATN and VSS, made the BS2 less susceptible to "resetting" itself from noise.


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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

chazRoman

MSD, I think you have a point.
I have a 5V DC wall adapter that isn't regulated (it puts out about 5.16V).
This led me to put the 5.16V through the regulator, which did run it, but maybe it does brown out.

I'll try replacing it with a 6V or so...

GICU812

I can never get my stamp to run off a 7805 (5v regulator) when its fed anywhere near 5v, it has to be much higher for it to work.

Mike Green

All regulators have a "drop out" voltage that's specified on their datasheets. Input minus output voltages less than the drop out voltage are not enough to maintain proper operation of the regulator. The LM78xx series regulators have a dropout voltage of 2V at 1A at 25 degrees C. The minimum input voltage for an LM7805 is 7V.

More recent voltage regulator designs have a lower drop out voltage. With some it's as low as 1/4V at low currents (50mA).