bs2p40 drops out when one of the Main I/O outputs is tured off

James D. Lane

Hi,
I have a bs2p40 main output going thru a ULN2803A which goes to a Potter Brumfield 5Vdc, 15mA relay.· The other side of the relay coil is tied to 5Vdc.· The ULN2803A is tied to 5Vdc and ground.· All of the listed devices share a common 5Vdc supplied by a LM7805C with a 10 uF capacitor·tied to the 12 Vdc input and a 1 uF capacitor tied to the 5 Vdc output.

When I turn on three of the outputs and then a few seconds later turn one of the outputs off, the 2p40 crashes.· I have tried running separate grounds for each of the devices back to the main supply terminal, I have monitored the 5Vdc supply when the 2p40 crashes and can not whitness any voltage noise caused by the relay dropping out.· I am only able to monitor for this at 240 samples/second so I may not be able to catch the noise event, I do not know.

Any ideas?
thanks,
James
·

KenM

Just for giggles, try to remove the relay from the circuit and try it again. The ULN2803A
has suppression diodes built in....but the device might not be doing it's job properly.


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Ken

Jon Williams

Maybe you have a bad relay. Swap LED circuits for the relays to see if you can get the program to run properly, then replace the relays 1-by-1.

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Jon Williams
Applications Engineer, Parallax