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Sebastian
04-13-2007, 04:35 PM
Hello,

Is there a way to tie an IO Pin on the STAMP to ground? (through coding, not a physical connection http://forums.parallax.com/images/smilies/smile.gif )

I am trying to control a device using the basic stamp that requires I short two wires. After some thinking, I realized this is not possible on the stamp without the use of a relay. I investigated the device I am controlling and found one of the wires is the same as ground.

So, this means that if I can ground the other wire, I make the 'connection' that I need, and activate the corresponding function on the device.

So, long story short, is there a way to make one of the STAMP's pins look like ground?

I am not in my lab at the moment, so I apologize about posting this idea without testing it first, but:

If I set a pin on the STAMP as an input, will it look like a virtual ground that flows very little current?

Is there some other way I could do this without the use of a relay?


Thank you in advance,
Sebastian

hitsware
04-13-2007, 05:09 PM
LOW,0 'makes pin 0, ground
HIGH,5 'makes pin 5, 5 Volts
INPUT,3 'makes pin 3, open

stamptrol
04-13-2007, 06:37 PM
Keeping in mind you cannot allow too much current to flow. As long as the controlled device draws something in the order of 20 mA everything should be fine.

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Tom Sisk

http://www.siskconsult.com
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Chris Savage
04-13-2007, 09:32 PM
Why not use a transistor to ground the signal? An NPN transistor or N-Channel MOSFET could be controlled from the Stamp I/O pin using a HIGH command to “ground” the other signal, depending on its properties.

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Chris Savage
Parallax Tech Support

Sebastian
04-14-2007, 12:38 AM
Thank you for the replies.

It looks like the STAMP can't do it on its own. I tried making a pin low, but it does not activate the device when connected to it - probably not enough current.

I was hoping not to need any other components, but your suggestion seems to be the easiest Chris. Looks like I have to go scavenging for a transistor array!

Sebastian

skylight
04-14-2007, 02:24 AM
did you tie the other wire to the stamps supply ground? if the device works by touching the two wires together and one wire is ground then using a stamp to ground the active wire would entail making sure that the devices ground(the one you think is ground)·is connected to the stamp ground for it to work.