View Full Version : Help With Active Low Switch Inputs

02-27-2005, 09:25 PM
Can someone kindly provide any insight into a (potential) power problem I am having with a BS2 project? Sure would appreciate the help!

I'm in the process of developing some circuitry for·a home automation system interface utilizing a·BS2. The circuit employs·4 normally open switch inputs (configured·5V active low with 10K ohm pull-up resistors) monitored via a standard·BUTTON command routine.··There are no other attached loads or inputs. The circuit/programming works perfectly but I've discovered that the connected power supply regulator (LM2940CT) gets really hot, indicating (to me) higher than anticipated·current. The STAMP itself doesn't appear to be hot - only the regulator. Up until now, my assumption has been that with a BS2 pin impedance of around 1 Megohm, current draw at 5V for switch inputs should have been astronomically small and therefore of little concern from a power management standpoint.·Now I'm starting to doubt that I really know enough about the way inputs work or that maybe I'm overlooking something basic.··Questions:

1. Is my assumption about input current draw correct?
2. Can there be programming issues involved?

Maybe I'm too close to the problem, but I'm not gettin' it. Anybody else ever see this? Any help would be very much appreciated. Thanks

02-27-2005, 11:11 PM
Try disconnecting EVERYTHING from the stamp except power. Still hot? No? Reconnect things 1 at a time. Even if all 4 resistors were tied to ground, that would be only an additional 2.5 ma from the onboard regulator. Double check the resistor values. If the circuit is wired as stated your problem should not be occurring. What is the stamp plugged into? Proto board? BOE? What is your raw unregulated dc to the stamp? More than +15 volts?


Post Edited (RickB) : 2/27/2005 4:14:00 PM GMT