Ummm... That shouldnt have happened... ( Oscope + AC + ZAP!)
GICU812
Posts: 289
Heres what I have, I was trying to play with the PIR sensor in a motion light, I have the light plugged in, with the HOT wire disconnected at the plug, there is no chance it was on.
My Parallax USB oscope ground was hooked on a cap, that I thought was in the DC section of the board I think it is anyway,·Im not going to mess with it anymore, but I wouldnt have hooked on it except I swore it was in the DC section.
My laptop·was having unrelated hickups, so I reached over to unplug the Oscope USB plug, as I unplugged it, my little finger dragged allong the bottom, I dont know if I was touching the USB connector, PC side of the USB connector, or maybe both, but I took a nice little jolt of 120AC
Well·my USB ports still work, scope still works, and my finger is fine though a little tingly.
This isnt the first time Ive had current seeping through my Oscope, Ive worked on projects in the past that were 5v with ground switched, powered·from my laptop USB for testing, and when hooked to the scope, and I turn off the projects switch, the stamp keeps running through the scope. I guess the scope grounds are frame grounded which grounds through the USB ground.
My Parallax USB oscope ground was hooked on a cap, that I thought was in the DC section of the board I think it is anyway,·Im not going to mess with it anymore, but I wouldnt have hooked on it except I swore it was in the DC section.
My laptop·was having unrelated hickups, so I reached over to unplug the Oscope USB plug, as I unplugged it, my little finger dragged allong the bottom, I dont know if I was touching the USB connector, PC side of the USB connector, or maybe both, but I took a nice little jolt of 120AC
Well·my USB ports still work, scope still works, and my finger is fine though a little tingly.
This isnt the first time Ive had current seeping through my Oscope, Ive worked on projects in the past that were 5v with ground switched, powered·from my laptop USB for testing, and when hooked to the scope, and I turn off the projects switch, the stamp keeps running through the scope. I guess the scope grounds are frame grounded which grounds through the USB ground.
Comments
And you say that you were switching ground instead of switching the 5V, which is also a very bad idea. Yes, since the configuration you list is powered all from the same supply, there's no reason why the black lead shouldn't provide a path back exactly the same as the power switch that was connecting to essentially the same USB (-).
I just thought some people might get a kick out of it, or at least something to think about next time they are working with thier scope.
Im still not sure how I got AC in that section of the circuit, I have since abandoned that project, having found a better solution. But the power going right into the circuit is at least rectified, the input power goes right to a diode set that powers the rest of the board, and a relay that actually turns the device on. Theoretically the only part that should have had AC was the relay contacts and the far end of the diodes. Im sure if I really wanted I could trace it out and see why this happened.
Post Edited (GICU812) : 9/13/2008 4:17:11 PM GMT
Sounds like a polarity issue with your electrical outlet. Do you have an outlet tester such as one of these? ...
www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100062242
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
I would not be without one of these. I use it all the time.
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
"I would not be without one of these. I use it all the time." ... lol - I just used mine this evening.
GICU812,
"Oh, another interesting thing I've always noticed.... "
That's normal where 60Hz is prevalent.... that's the grid, it's everywhere, it transmits like an antenna and your scope picks it up. In other countries you would see 50Hz as the normal.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 9/14/2008 4:07:30 AM GMT
Jeff T.