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Author Topic: brain storm an optimal human safety system for back line  (Read 96295 times)

Mark Cadwallader

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Re: brain storm an optimal human safety system for back line
« Reply #390 on: November 07, 2015, 12:55:15 am »

Mark, 30 years ago you could have stepped into any place on Last Chance Gulch and found who knows what.

Whatever became of the Iron Front Hotel?

Tim, I'm pretty sure that is still the case. The Gold Bar and the Western are still there, as is the Rialto. O'Tooles closed a couple of years ago; Rose O'Toole died about two years ago. The Iron Front Hotel is still there; folks are sleeping there tonight.  There is probably less change on the Gulch than you would think (or hope).
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #391 on: November 07, 2015, 09:10:46 am »

Look for old buildings with brand new receptacles. Churches are suspect since may of their stages have been "upgraded" to grounded outlets. That's where the painters and DIY guys do their wiring mischief.
Yup churches are target rich environments but they'll probably want you to fix them free.

JR
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

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Re: I hate it when a plan doesn't come together.
« Reply #392 on: November 09, 2015, 12:28:22 pm »

I just tested with 100M input resistors and the MOSFET buffer doesn't stay turned off... Both line and neutral LEDs glow dimly. Then when I touch the probe the correct LED gets brighter but the wrong LED still doesn't go completely dark.

Which leaves me with two options.

#1 revisit the design to figure out why it is doing what it is doing and see if i can make it work with 100M input Z.

#2 lobby UL to allow <100M insulation between mains and human touch points. I have no doubt that the uAs of leakage from mine are harmless, but that may not matter.

For now I will need to chew on #1 a little more, but it will probably involve more parts and more complexity.

JR

PS: For chuckles I plugged the cheap outlet tester into my kitchen outlet that gave the false hot ground reading before I fixed that. The cheap tester says hot ground, and this is with the leaky mixer unplugged. So false reports a problem that isn't there, while ignoring real problems.  :o
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #393 on: November 09, 2015, 02:53:58 pm »

OK Door #1 is still open...

By adding one new part** I have it working again with 100M input Z.  ;D

So if 2mA is acceptable brightness for ground present LED I have met all difficult UL stipulations (AFAIK).

Note: They apparently make a green neon lamp (blue too), so if 2 mA green LED is not bright enough I could use a green neon lamp for that. (I haven't found a source or price yet, but see them around in use).

I have to do one more PCB layout to meet UL spacing requirements but no major changes so I can stick with existing form factor.

I have a couple different replacement plugs on order to determine the best one to repurpose...They are already UL approved so that should simplify my approval. My new plan is to package my PCB inside a currently available plug. So I don't have to tool anything myself besides the PCB.

Another large step forward.  8)

JR


*** as has been my strategy for several months now I have stopped sharing design details  :P

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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #394 on: November 09, 2015, 03:29:14 pm »

Note: They apparently make a green neon lamp (blue too), so if 2 mA green LED is not bright enough I could use a green neon lamp for that. (I haven't found a source or price yet, but see them around in use).

I think the blue and green neon lamps actually glow orange inside; the bulbs are colored glass. I could be wrong, but that's my understanding. If that's the case, they may not be bright enough for your purposes.

I suppose they could use other gases or impurities to get it to glow different colors, but that might increase the cost of manufacturing by a few cents.

If the bulb is actually clear and the ionized gas glows the proper color, that's probably a benefit.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #395 on: November 09, 2015, 04:34:15 pm »

I am not overly enthusiastic about green neon but one of the plugs I ordered has one inside... apparently the normal neon lamp color makes people uncomfortable when coming from inside an electrical plug.  :o



A mixture of neon and krypton (superman?) will glow green, but green is commonly phosphor based (excited by UV)

I am more concerned about cost and availability. Too exotic for me... I don't even like the blue LED.

JR

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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #396 on: November 12, 2015, 12:32:23 pm »

Found a nice plug to shoe horn my tester PCB into.  Right angle plug with clear housing big old screw head in the middle of the back to serve as the touch probe.

Not cheap, but cheaper than tooling up my own UL approved package.  8)

JR
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Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #397 on: November 18, 2015, 04:39:58 pm »

While one of my two beta testers is lost in space, the one who is actually testing outlets with one and reporting back suffered our first field failure.

It took me a while to fix it because I didn't see anything obvious (I expected a broken wire or bad solder connection). I had to carefully set up my bench and scope to look at voltages with the tester plugged in. You don't just fool around with mains voltages, even our puny 120VAC. I eventually found that the MOSFET had gone bad...

My current thinking is 2 possibilities; 1- the mains voltage spiked in excess of the device breakdown voltage, or 2- a static hit to the touch probe. (Door number two is looking good since gate was low impedance to drain <200 ohms).

The good news is I can drop a 50% higher voltage part into the same foot print, and the new improved 100M input network  should reduce stress from external static hits to the touch probe.

I need to figure this stuff out now rather than find out later.

JR

note: there is a zener diode clamp across the gate that in theory should eat any static hit, but it looks like the gate is what broke.
« Last Edit: November 18, 2015, 04:48:16 pm by John Roberts {JR} »
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Jonathan Johnson

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Re: brain storm an optimal human safety system for back line
« Reply #398 on: November 19, 2015, 12:16:55 am »

JR, in the event that you succeed in bringing this to market, and I really hope you do, do you have a suggested retail price in mind? Or is it too soon for that? I'd like to commit to buying one if the price is reasonable... but our ideas of "reasonable" might be different. ;-)
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Tim McCulloch

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Re: brain storm an optimal human safety system for back line
« Reply #399 on: November 19, 2015, 01:14:59 am »

JR, in the event that you succeed in bringing this to market, and I really hope you do, do you have a suggested retail price in mind? Or is it too soon for that? I'd like to commit to buying one if the price is reasonable... but our ideas of "reasonable" might be different. ;-)

Reasonable is a relative term for whatever value is derived from ownership and use.  I see this as a teaching tool that has great practical value and I'd be willing to spend a bit more, perhaps, because of the dual purpose.

How much?  Not sure yet, but I think the home inspector guys would snap these up at $30 - $40.

The market for this device is much greater than our little world.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut
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