On Wednesday 01 July 2009, alan battersby wrote: >Hello everyone, >I thought that I would make a probe for my setup. My idea was to have >one fixed plate and one movable plate attached to the probe head. These >plates are initially in contact and move apart as the probe hits the >surface thus breaking contact like a switch. I built this and tested >away from the computer and it seemed to work ok, when the plates touch >the output is 5v dropping to 0v when plates are apart. But connecting >it up to pin10 of the parallel port of my laptop I found that when the >connection between the plates is broken the voltage only drops to 4.6v >and so emc doesnt pick this up as a trigger. Would someone please tell >me why the voltage does not drop to zero as I expected it too? Is a >switch insufficient for the task? I am fairly sure that I configured emc >correctly, however my knowledge of electronics is very very basic. Also >I checked the port BIOS settings which are ECP & EPP. > >Thanks >Alan > Most logic circuits have a considerable 'pullup' in that a floating input is quickly pulled high. What you want is to have that input shorted to ground when the switch is closed, and about a 5 to 10 K resistor to enhance the pullup speed a bit when the switch opens, and to register the contact on the rising edge of this signal. >---------------------------------------------------------------------------- >-- _______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users
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