Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: rcotteleer on January 08, 2006, 07:24:29 AM
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I am attempting to wire up limit and spindle index sensors using some small honeywell opticals. I have a 10K pull up in the circuit. My issue is that it does not seem that the circuit will draw the port pins low consistently. It will draw the port down to ~1.4V when bread boarded and 1.8V when soldered to a piece of PCB.
When first connected it work fine, when I block the sensor, it drive the output high (~4.5v) when I unblock the sensor, the voltage does not go low enough to reset the LED on the Mach 3 Diagnostics screen.
Basic schematic
to LPT Pin
l
10K l NPN
+5v-----^^^^^-------l------------\_/-------- Gnd
I have tried using larger pullups , up to 1M, it doesn't seem to make a significant difference.
Any thoughts?
Randy
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Have you tested it by taking the pull up off? You are pulling the port down and what you are getting from the resistor. I don't know your sensor but it may only be able to sink a very small amount of current.
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Brian,
Thanks, that worked, the schematic now looks like this:
To LPT Pin
l
l NPN
l------------\_/----------Gnd
Am I correct in assuming that now the transistor is now simply sinking the current from the port, whereas before it was trying to sink the port and the power coming through the resistor?
BTW here is the link to the sensor: http://catalog.sensing.honeywell.com/datasheet.asp?FAM=infrared&PN=HOA1887%2D012
Thanks for your help
Randy