Post by thread:[EE] Current Probe?

A tech just came to me with a problem on a board. A PIC is TRYING to drive a line to 3.3V, but it's only getting to 1.9V. So, something somewhere is holding it down. Has anyone had any luck with Hall effect current probes in tracing where current is going on a board? What particular probe are you using? THANKS! Harold -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

On Tue, Mar 23, 2010 at 12:20 PM, Harold Hallikainen <spam_OUTharoldTakeThisOuThallikainen.org> wrote: > A tech just came to me with a problem on a board. A PIC is TRYING to drive > a line to 3.3V, but it's only getting to 1.9V. So, something somewhere is > holding it down. Has anyone had any luck with Hall effect current probes > in tracing where current is going on a board? What particular probe are > you using? > That's quite a bit of current. The PIC has output resistance of ~35 ohms IIRC, so maybe 50 mA? You should be able to find the current sink with a good voltmeter. To increase the resolution, measure from the PIC pin to other places on the node in microvolt range. Largest drop is the winner. Never used a hall effect current probe. Regards, Mark markrages@gmail -- Mark Rages, Engineer Midwest Telecine LLC .....markragesKILLspam@spam@midwesttelecine.com

On 3/23/2010 10:17 AM, Mark Rages wrote: > > That's quite a bit of current. The PIC has output resistance of ~35 > ohms IIRC, so maybe 50 mA? You should be able to find the current > sink with a good voltmeter. To increase the resolution, measure from > the PIC pin to other places on the node in microvolt range. Largest > drop is the winner. I'll second Marks comment of using a voltmeter. That has worked well for me for finding short circuits. It helps to have access to a 5 or 6 digit system meter...

I have an old HP current probe that works well for this. Just make sure the little white dot is pointed in the direction that the trace is running in. I find that the probe works best with high-current pulses best, although it will trace a DC current. The little thumb-wheel pot on the side of the probe sets the sensitivity. I also (years ago) purchased something called a "Leak Seeker" that is specifically designed for this kind of trouble-shooting. It is essentially a high-resolution DC voltmeter that controls the pitch of a tone. Its really cool in that it auto-zeros itself as you progress along the trace(s) heading in the direction of the short. You don't need to watch a meter - just listen to the tone as you move the needle-point probe from place to place along the trace. The fine-tip needle easily penetrates the solder mask. Its actually worked really, really well the several times that I've used it. Do note that its designed to locate DC faults (as opposed to pulses). dwayne At 11:20 AM 3/23/2010, Harold Hallikainen wrote: {Quote hidden}>A tech just came to me with a problem on a board. A PIC is TRYING to drive >a line to 3.3V, but it's only getting to 1.9V. So, something somewhere is >holding it down. Has anyone had any luck with Hall effect current probes >in tracing where current is going on a board? What particular probe are >you using? > >THANKS! > >Harold -- Dwayne Reid <dwaynerKILLspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax http://www.trinity-electronics.com Custom Electronics Design and Manufacturing

Dwayne Reid wrote: > I also (years ago) purchased something called a "Leak Seeker" that is > specifically designed for this kind of trouble-shooting. It is > essentially a high-resolution DC voltmeter that controls the pitch of > a tone. Its really cool in that it auto-zeros itself as you progress > along the trace(s) heading in the direction of the short. > > You don't need to watch a meter - just listen to the tone as you move > the needle-point probe from place to place along the trace. The > fine-tip needle easily penetrates the solder mask. > > Its actually worked really, really well the several times that I've > used it. Do note that its designed to locate DC faults (as opposed to > pulses). Are these devices available nowadays? Anybody got a model number? Vitaliy

On 3/23/2010 4:07 PM, Vitaliy wrote: > Dwayne Reid wrote: >> I also (years ago) purchased something called a "Leak Seeker" that is >> specifically designed for this kind of trouble-shooting. It is >> essentially a high-resolution DC voltmeter that controls the pitch of >> a tone. Its really cool in that it auto-zeros itself as you progress >> along the trace(s) heading in the direction of the short. >> >> You don't need to watch a meter - just listen to the tone as you move >> the needle-point probe from place to place along the trace. The >> fine-tip needle easily penetrates the solder mask. >> >> Its actually worked really, really well the several times that I've >> used it. Do note that its designed to locate DC faults (as opposed to >> pulses). > > Are these devices available nowadays? Anybody got a model number? > > Vitaliy > Maybe it's this one: http://www.eds-inc.com/eds82.html

I still use an old Wavetek handheld dmm that has that same kind of reading-to-audio-tone function for finding shorts and intermittent connections. It's really handy and a shame that all meters don't have this same thing. On 3/23/10, Vitaliy <.....piclistKILLspam.....maksimov.org> wrote: {Quote hidden}> Dwayne Reid wrote: >> I also (years ago) purchased something called a "Leak Seeker" that is >> specifically designed for this kind of trouble-shooting. It is >> essentially a high-resolution DC voltmeter that controls the pitch of >> a tone. Its really cool in that it auto-zeros itself as you progress >> along the trace(s) heading in the direction of the short. >> >> You don't need to watch a meter - just listen to the tone as you move >> the needle-point probe from place to place along the trace. The >> fine-tip needle easily penetrates the solder mask. >> >> Its actually worked really, really well the several times that I've >> used it. Do note that its designed to locate DC faults (as opposed to >> pulses). > > Are these devices available nowadays? Anybody got a model number? > > Vitaliy > > -

{Quote hidden}> > On Mar 23, 2010, at 7:24 PM, Lucas Thompson wrote: > > I still use an old Wavetek handheld dmm that has that same kind of > reading-to-audio-tone function for finding shorts and intermittent > connections. It's really handy and a shame that all meters don't have > this same thing. > > On 3/23/10, Vitaliy <EraseMEpiclistspam_OUTTakeThisOuTmaksimov.org> wrote: >> Dwayne Reid wrote: >>> I also (years ago) purchased something called a "Leak Seeker" that >>> is >>> specifically designed for this kind of trouble-shooting. It is >>> essentially a high-resolution DC voltmeter that controls the pitch >>> of >>> a tone. Its really cool in that it auto-zeros itself as you >>> progress >>> along the trace(s) heading in the direction of the short. >>> >>> You don't need to watch a meter - just listen to the tone as you >>> move >>> the needle-point probe from place to place along the trace. The >>> fine-tip needle easily penetrates the solder mask. >>> >>> Its actually worked really, really well the several times that I've >>> used it. Do note that its designed to locate DC faults (as >>> opposed to >>> pulses). >> >> Are these devices available nowadays? Anybody got a model number? >> >> Vitaliy > > > > Does anyone have a block diagram of the ( voltage ? ) reading-to-audio- tone electronics ? Gus

> Does anyone have a block diagram of the ( voltage ? ) > reading-to-audio-tone electronics ? Taking that almost unbelievable question at face value. 1. Draw rectangle Label rectangle "VCO" Add input - label Vin. Add output - label Fout QED. or 2. Use CD4046 block diagram. Essentially as above with a few support components thrown in to set frequency per Volt etc. http://focus.ti.com/lit/ds/symlink/cd4046b.pdf 3. For extra points add a simple differential amplifier which amplifies the small voltage beteen its probes to a level that best suits the 4046. Russell

> > Does anyone have a block diagram of the ( voltage ? ) > > reading-to-audio-tone electronics ? > 2. Use CD4046 block diagram. > Essentially as above with a few support components thrown in to set frequency per Volt etc. > > http://focus.ti.com/lit/ds/symlink/cd4046b.pdf This may work better. The other tends to crash on loading. May just not like being readf uiopside down. http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/CD4046BC.pdf R

> -----Original Message----- > From: piclist-bouncesspam_OUTMIT.EDU [@spam@piclist-bouncesKILLspamMIT.EDU] On Behalf > Of Mark Rages > Sent: 23 March 2010 17:18 > To: Microcontroller discussion list - Public. > Subject: Re: [EE] Current Probe? > > On Tue, Mar 23, 2010 at 12:20 PM, Harold Hallikainen > <KILLspamharoldKILLspamhallikainen.org> wrote: > > A tech just came to me with a problem on a board. A PIC is TRYING to > drive > > a line to 3.3V, but it's only getting to 1.9V. So, something somewhere > is > > holding it down. Has anyone had any luck with Hall effect current probes > > in tracing where current is going on a board? What particular probe are > > you using? > > > > That's quite a bit of current. The PIC has output resistance of ~35 > ohms IIRC, so maybe 50 mA It depends on the particular PIC being used, but they are typically a lot weaker sourcing current with a 3v supply than 5v. The 12F617 I have been using recently shows an equivalent output resistance of ~150 Ohms at 25 degrees Celsius with a 3v supply and small currents (< 4.0mA), and somewhat more than double that at 125 degrees Celsius. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================