Sometimes a situation occurs that is just out of reach for the scope=20 you have available. The only solution that always works is to use a=20 logic probe constructed with the same family of circuitry that you are=20 testing patched onto the tested circuit with the shortest possible=20 leads. It is only hard the first time you do it... John Ferrell W8CCW A wise and frugal government, which shall leave men free to regulate=20 their own pursuits of industry and improvement, and shall not take from=20 the mouth of labor the bread it has earned - this is the sum of good=20 government. Thomas Jefferson=20 On 8/19/2010 12:00 AM, Forrest W Christian wrote: > My most recent project has created a new challenge for me. I use a > TDS2014 4 Channel DSO on the bench, and to date, just some good garden > variety 1X/10X scope probes (basically decent quality but not really > name-brand probes - maybe pomona or tenma or something like that). > > This new project involves putting 120us holes in 60VDC. The stuff is > basically done at this point, but I think I've spent almost more time > dealing with scope grounding issues than actually solving problems. > Switching 60VDC off and on that quickly obviously creates some > interesting inductive possibilities. For instance, earlier today I was > seeing some stray spikes on one of the signals being monitored. Pulled > the scope probe out of it's 'grabber clip thingy (yes technical I > know)', and touched the tip to the grounding clip (you know, the one > with about 3 inches of wire attached directly to the probe itself). > Amazingly, the spikes were *still* there. Ended up disconnecting all > the other grounds on the other probes and referencing only to that one > to verify that signal was clean. Of course, then all the other signals > weren't clean anymore - at least not on the scope. > > So, I figured to fix this in the future, I'd spend a bit and get some > differential scope probes. So I glanced on ebay and google for costs > and availability - and in the process about fell out of my chair in > shock. Maybe there's a decent one out there at a reasonable cost that > I'll find, but looks like they're few and far between. > > So, before I either just suffer - or go out and buy a few isolation > amplifier ICs and build my own, I figured I'd ask on here if there are > either some tricks I'm missing (I.E. maybe it's the scope probes I'm > using - a $30-50 probe just isn't good enough, OR there is some other > way to get a good picture of what a signal looks like referenced to > ground near the chip producing it - when you have 4 possible grounding > points. > > Ideas? > > -forrest > > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .