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3.3V logic probes?

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 10 April, 2009 » 3.3V logic probes? « Previous Next »

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epithumia
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Username: epithumia

Post Number: 634
Registered: 06-2006

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Posted on Friday, 27 March, 2009 - 11:19 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was bemoaning that fact that I haven't got a logic probe that works on a 3.3V supply. An oscilloscope doesn't quite work because it can't always tell the difference between ground and floating.

I took a look at the usual suppliers, RS, Farnell, Rapid, and was surprised to see that the offered crop of logic probes all require at least 4V supply.

Has anyone seen a 3.3V logic probe? It needs it detect fast edges and floating signals.

Thanks,
Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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alexr
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Username: alexr

Post Number: 46
Registered: 02-2008

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Posted on Friday, 27 March, 2009 - 11:43 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

You can get this one in kit form or since its a Silicon Chip project you could wait a couple of years for it to appear in EPE.
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epithumia
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Username: epithumia

Post Number: 635
Registered: 06-2006

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Posted on Friday, 27 March, 2009 - 12:08 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks. I spotted that Silicon Chip had a project, but didn't know about the kit.


quote:

It's capable of picking up a pulse only 50mS (sic) long




Only 50 milliseconds? I'm working in the nanosecond region.

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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joe
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Username: joe

Post Number: 531
Registered: 05-2005

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Posted on Friday, 27 March, 2009 - 12:37 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Create a simple potential divider, say 2 x 4.7k resistors, 1 end connected to ground and the other end connected to +v (3.3v in your case).
Connect the resistor junction to your scope input, and your scope probe to the same junction point.

This will create a midpoint on the scope display indicating when the input is floating.

Joe
Do one thing each day that scares you – work here !

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