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Author Topic: brain storm an optimal human safety system for back line  (Read 95433 times)

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #320 on: August 19, 2015, 08:31:52 pm »

I have heard (anecdotally) that 12V can deliver a fatal shock, if the resistance between the point of contact and the moist tissues of the body is low enough. I am not willing to test the veracity of this claim.

So don't go and pinch your fingers in the jumper cables when you hook up to your car battery.  :o
You can't look at voltage in isolation. Current is what does the damage and current is dependent on voltage "and" resistance.

A 1.5V AA cell could kill you if someone drives it deep into your heart.  :'(

!2V seems relatively harmless in most ways we would normally encounter it. I wouldn't take a bath with a car battery in the tub, but the acid and mess might be worse than the electrical shock hazard.

JR
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Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #321 on: August 20, 2015, 08:43:09 am »

You can't look at voltage in isolation. Current is what does the damage and current is dependent on voltage "and" resistance.

A 1.5V AA cell could kill you if someone drives it deep into your heart.  :'(

!2V seems relatively harmless in most ways we would normally encounter it. I wouldn't take a bath with a car battery in the tub, but the acid and mess might be worse than the electrical shock hazard.

JR
If you have cuts on your hands, even touching the copper tips on 12-volt jumper cables can be very painful since your epidermis layer has bee breached, but I don't think it's life threatening. And a 9-volt battery on the tongue is pretty zippy, but the current would never even get near your heart. According to some charts I've seen, DC shocks require about 3X as much voltage as AC shocks for human electrocution. That's because 60 Hz seems to be the perfect frequency to disrupt human heart rhythm and put it into ventricular fibrillation. When the paramedics arrive and use a de-fibrillator on you, there's a bunch of capacitors dumping DC into your chest and heart. That causes all your heart muscles to contract at the same time, resetting it to normal operation just like rebooting your computer.

I actually knocked myself unconscious and rebooted my heart at the same time when I was 22 years old. I was holding the chassis of a tube amp (an SVT bass head) with my left hand, and poking around the 600-volt DC supply with a screwdriver held in my right hand. My hand slipped and contacted the shaft of the screwdriver while it was touching a big capacitor, and I can remember my arm flying up over my head and blacking out. I woke up laying in the corner after an unknown amount of time, and I'm pretty sure that if this would have been a 600 volt AC shock I would probably have died. But since it was a 600 volt DC shock, I stopped and restarted my heart at the same time. Just dumb luck I wasn't killed, but I gained a healthy respect for electricity after that incident.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #322 on: August 20, 2015, 07:34:59 pm »

One step forward one step back...

The mosfet footprint is wrong and I think I built that footprint from scratch so if it's wrong, I did it.  :'(

The mosfet is the black thing about the size of hungry wood tick in the picture.

Over 20 discrete parts on that tiny PCB , I'm too old to hand pop SMD...

JR

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Steve M Smith

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Re: brain storm an optimal human safety system for back line
« Reply #323 on: August 21, 2015, 02:54:45 am »

But since it was a 600 volt DC shock, I stopped and restarted my heart at the same time

Are you sure about that?!  This reminds me of all of those silly TV programmes which show a defibrillator being used to start a stopped heart... That's not what they're for and they can't do that.  I have a son who is a trainee paramedic who points out these things.

Over 20 discrete parts on that tiny PCB , I'm too old to hand pop SMD...
Does your Chinese PCB vendor not offer a population service?  If not, you should easily be able to find a company who can supply built PCBs.

Steve.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #324 on: August 21, 2015, 09:57:39 am »


Does your Chinese PCB vendor not offer a population service?  If not, you should easily be able to find a company who can supply built PCBs.

Steve.
While prototypes are getting more accurate, I need to prove that the design is correct before I even think about having some built, and as I mentioned the mosfet footprint is wrong so back to the drawing board...

I would use a US contract manufacturer "IF" I were to build any number of these, but those guys don't want to turn on the machines for less than 250 units or more. I am apprehensive about getting into that business (would need UL and more) .

 For now I need to confirm that this works (if I can connect the mosfet to the wrong pad spacing). It's hard enough with a good pad layout.

JR

PS: I suspect the defibrillator is used to stop fibrillation.  :o  Kind of like reseting the heart to override the ineffective, too-fast heart rate, so a natural rhythm can take over again. It is a TV cliche to restart a stopped heart, kind like the way that every PA system on TV makes feedback.
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Stephen Kirby

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Re: brain storm an optimal human safety system for back line
« Reply #325 on: August 21, 2015, 12:58:12 pm »

There are folks around these parts who will hand build 10 of something.  And you can often find someone at a CM who will do piece work at home.  Solectron got in big trouble a few years ago for doing too much of this.  It was one thing for supervisors to give some prototypes to people to build at home instead of firing up the lines, it was another when they were doing production work for major customers.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #326 on: August 21, 2015, 01:10:40 pm »

There are folks around these parts who will hand build 10 of something.  And you can often find someone at a CM who will do piece work at home.  Solectron got in big trouble a few years ago for doing too much of this.  It was one thing for supervisors to give some prototypes to people to build at home instead of firing up the lines, it was another when they were doing production work for major customers.
Yes I know of some guys doing their own hand pops (over on the DIY forum)... I might get them to do a few for me but I'd probably need to order a stencil (I didn't).

We'll see,,,It turns out I made the mosfet footprint leads on a 1mm pitch when the part is actually 1.5mm pitch so that's awkward to put it kindly. If I can cheat it I might build one or two to prove out the part values. and maybe get a real company interested.  ;D

JR
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #327 on: August 21, 2015, 02:57:36 pm »

We have lights and action.

This is the light show for my intentional RPBG test outlet..

The far left green LED indicates ground present (it can't tell bootleg from real ground)
The next green LED for line hot is dark.
The red LED for ground hot is on... ;D (danger Will Robinson)
The yellow LED for neutral hot is also on. (warning)

It works..... 8)  If I plug it into my bench outlet I get just the single yellow LED because that outlet is swapped line-neutral and lacks a ground. Testing other outlets around my house I get mostly single green for line hot, open ground.

I think it's a mistake to have the ground LED next to the line, since it will be harder to see than if they are spread apart. Especially inside the plastic housing. I can swap the green line LEDs with the Yellow neutral LEDs then swap line and neutral input to get a better order. Then it would be green (ground, present) yellow(neutral hot), red (ground hot), and green (line hot). So green are the two outside LEDs.  The ground LED is not in the same line with the others but everything is so tight you can't see that small difference.

I had one open connection and one solder bridge on the board... not bad for a tired old man hand-popping tight SMD.

I need to see how hard it is to cheat the mosfets into the incorrect foot print, might build a couple more (but not 24 of them).

JR
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Stephen Swaffer

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Re: brain storm an optimal human safety system for back line
« Reply #328 on: August 21, 2015, 05:51:52 pm »


We have lights and action.



In the context of a concurrent thread this intro gave me pause..

Maybe a bit a light at the end  if the tunnel it seems! 
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Steve Swaffer

John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #329 on: August 23, 2015, 12:10:20 pm »

Got a chance to do some field testing and with the plastic cover the green ground present LED, right next to the green line good LED makes it harder to see the line LED.  I will definitely swap the line with neutral so greens are the two outside LEDs.

I tested my next door neighbor's garage/workshop (that he wired himself). He seemed a little nervous while I tested, but every outlet tested good, grounds present and green for line hot. :-)

I do not love the clear plug package..diffuses the LED light too much. 

JR
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