Using counters with magnetic sensor, melexis US4881LUA. Low Voltage? In a bind, need input ASAP.

[Ralph@NES]

Hello

I'm in a bit of a quandry.  I need to measure RPM of a bearing cage via sensing passing magnets embedded in the cage.  My problem is further compounded by the fact that the aperture to sense these magnets is very, VERY small.  Less than .200" of a gap for me to squeeze a sensor into.

I selected a sensor, the Melexis US4881LUA-ND, which is a very small transistor style sensor:

http://www.melexis.com/prodfiles/0004821_US4881_rev011.pdf

http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=US4881LUA-ND

I connected it to my PCI-6602 card, which has several counters.  I'm referencing the sensor directly from the +5v on the card and using PFI38 and the R Ground for my connections.  Across the VSS (input) and signal (output), I've connected several different resistors from 100 ohm to 10k.  No matter what I do, the most voltage I get out of the sensor is about .7v.  In order for my card to accurately read frequency, it appears that I need 0 and 5v, or a TTL signal, right?

My questions are as follows:

Can I make the counter work with 0 and .5 or .7 volts instead of 0 and 5, and if not

Can someone recommend a tiny sensor that WILL give me five volts?

I'm really in a corner on this...  Any help is greatly appreciated!

[AnalogKid2DigitalMan]

Hi Ralph:

VSS is ground on the device. The pullup resistor connected to the output has to go to VDD (+5V in your case). Did you mix up the connections for VSS and VDD?

-AK2DM

[Ralph@NES]

It's been a long day man...  If anyone needs me, I'll be the guy beating his head off the desk for not catching that :manmad:

Now it's at least showing 4v and 0 with a 10k.  Is this going to work or do I need to keep messing around til I get 5?  What do you think the chances are I screwed up the sensor by wiring it backwards?

[AnalogKid2DigitalMan]

Yes, a 0 to 4 V range should work for the input. Looks like there is no internal reverse-voltage protection the the device, so yes, it could be damaged.

Try it out anyways and Good Luck.

edit- Don't bang your head too hard, you might lose your bearings

-AK2DM

Message Edited by AnalogKid2DigitalMan on 08-02-2007 01:20 PM

[Ralph@NES]

For some reason I can't get a reading with frequency or counter with this setup, although on the very same channel I can connect a Cherry Corp. proximity sensor and get accurate RPM and frequency.  I'm thinking I've still got something wrong, even though the connections are right and I'm using the recommended 10k resistor.  I'll try again with a new sensor, try the cherry again in hopes that I didn't hurt my board (it shouldn't have since it was referenced to its' own 5v source, right?) and report back.  I may need some more assistance on this and thanks much in advance.

Ralph