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Author Topic: brain storm an optimal human safety system for back line  (Read 102050 times)

Stephen Kirby

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Re: brain storm an optimal human safety system for back line
« Reply #310 on: August 18, 2015, 01:53:05 pm »

My original order was kicked because my gerber files had different file extensions than they like,,, My version of layout software is probably 20 years old... :-) So far I don't know (yet) that my updated file package has been received and acceptable.

JR
If you can, send ODB++ files.  Gerber is open to a lot of interpretation.  If the Gerbers were 274X they shouldn't care what extensions were used.  Although in my CM life, it drove me nuts when people used the extension to denote which layer it was.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #311 on: August 18, 2015, 02:13:17 pm »

If you can, send ODB++ files.  Gerber is open to a lot of interpretation.  If the Gerbers were 274X they shouldn't care what extensions were used.  Although in my CM life, it drove me nuts when people used the extension to denote which layer it was.
Yup my files were 274x gerbers... But for $14 flat fee I don't expect much hand holding... I don't mind renaming the files.

24 boards for $14 is just crazy cheap ($0.58).... admittedly they are tiny boards but quality looks OK from quick inspection.

3 weeks shipping is not great, but you get what you pay for and I didn't pay for fast...

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Kirby

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Re: brain storm an optimal human safety system for back line
« Reply #312 on: August 18, 2015, 02:28:04 pm »

Sounds like one panel.  There might have been more that they threw away.  Pretty darn good price for a one off.  Most of the big shops are retooling for any layer blind/buried vias and there's a lot of left over conventional capacity.  One panel, double sided, probably only spent a day in the shop.  Cost of tracking it though the shop probably exceeds the parts themselves.  If you don't mind, I'd like to know who did this for you.  We occasionally need little test interface boards.

A couple of years ago I was trying to find someone to make a small batch of boards for testing solderpastes down to the smallest features.  Ended up with Tripod in China as the only people who could make it and got very good pricing as well compared to local shops who couldn't get the small features reliably.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #313 on: August 18, 2015, 04:00:12 pm »

Sounds like one panel.  There might have been more that they threw away.  Pretty darn good price for a one off.  Most of the big shops are retooling for any layer blind/buried vias and there's a lot of left over conventional capacity.  One panel, double sided, probably only spent a day in the shop.  Cost of tracking it though the shop probably exceeds the parts themselves.  If you don't mind, I'd like to know who did this for you.  We occasionally need little test interface boards.

A couple of years ago I was trying to find someone to make a small batch of boards for testing solderpastes down to the smallest features.  Ended up with Tripod in China as the only people who could make it and got very good pricing as well compared to local shops who couldn't get the small features reliably.
Sure it's no secret... I got the tip on another DIY website. I've been buying PCB from china for years. even when I order them from US or Canada.  :o

http://dirtypcbs.com/

they offer a few fixed price deals my $14 was for 5x5 cm, they also have a $25 10x10cm deal...

the proto board count is nominally 10 pcs but +/- a few... My + was 24 pcs,,,

I suspect they nest a bunch of different projects together to fill a standard panel and I got lucky, probably the last job on that panel.

Unless you are willing to wait 3 weeks for the free shipping like I did you can upgrade to quicker shipping, costing a bunch more than the boards, but that the nature of things these days.

JR

PS I've used other chinese proto board shops that were more like $100 for how ever many boards you can get out of a standard panel.. but this deal is crazy cheap.
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Stephen Kirby

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Re: brain storm an optimal human safety system for back line
« Reply #314 on: August 18, 2015, 05:01:16 pm »

I love it!  readme's? get out of here :)

5/5 on 1oz ain't bad for cheap.  Even colored mask which can be a pain to image, and they're holding 3mil webs with it.

There used to be a proto shop out here called NBS which literally stood for No B.S.  Box-o-parts and a napkin, no problem.  Unfortunately they got some bigger contracts, expanded and couldn't sustain it. 
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #315 on: August 18, 2015, 06:27:44 pm »

I love it!  readme's? get out of here :)

5/5 on 1oz ain't bad for cheap.  Even colored mask which can be a pain to image, and they're holding 3mil webs with it.

There used to be a proto shop out here called NBS which literally stood for No B.S.  Box-o-parts and a napkin, no problem.  Unfortunately they got some bigger contracts, expanded and couldn't sustain it.

Yup the website is a bridge to a taobao supplier in china... so no speaky the english at the board house.

I always thought read-me's  were redundant .

JR
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Don't tune your drums half-ass. 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 #316 on: August 19, 2015, 11:36:06 am »

Not news but worth reviewing...



FWIW I've felt current < 1 mA but not a big deal. The actual current you will experience often depends hugely on skin resistance which varies with moisture (sweat).

Note: I sized the GFCI stinger cap to be > 6 mA to trip the GFCI but < 10 mA to be below the let-go threshold. 

The probe current for outlet tester is perhaps tens of uA...

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Mike Sokol

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Re: brain storm an optimal human safety system for back line
« Reply #317 on: August 19, 2015, 01:42:59 pm »

Not news but worth reviewing...



FWIW I've felt current < 1 mA but not a big deal. The actual current you will experience often depends hugely on skin resistance which varies with moisture (sweat).

Note: I sized the GFCI stinger cap to be > 6 mA to trip the GFCI but < 10 mA to be below the let-go threshold. 

The probe current for outlet tester is perhaps tens of uA...

JR

Good chart. Plus it's good to be aware that skin resistance is highly non-linear in nature and varies by voltage. That is, your body doesn't follow a simple I=E/R relationship like a resistor. It's a bit  logarithmic in nature, with current rising more rapidly than the voltage due to a "punch through" effect of the epidermis skin layer. Once the epidermis layer "insulation" has been breached, then there's a much higher current flow. I generally use 1,500 ohms as a base calculation for electrocution, but as JR also point out, this changes a lot with skin moisture. Of course, I can think of few situations more likely to induce maximum shock current than standing on stage with sweaty hands on your metal guitar strings and touching a wired mic with your wet lips. Well, perhaps standing in a baptismal pool with a wired mic or electric guitar in your hand should be at the top of the "Don't Do It" list.
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John Roberts {JR}

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Re: brain storm an optimal human safety system for back line
« Reply #318 on: August 19, 2015, 02:12:19 pm »

I've thought about this a bunch and I don't know that the skin resistance is non-linear, but the human body is not a simple homogeneous resistor. Our core which is like a dilute salt water solution is pretty conductive. The skin layer is not a great conductor especially when dry, but rarely completely dry..

The crusty old electricians who show off by grabbing live wires have (dry) callused hands to protect them.

Another variable is how tightly you grip the conductor.. grabbing tighter will deliver lower resistance.

Since electricity follows the lowest impedance path, it doesn't travel from hand to hand just on your outside skin, but inside your body where the bad stuff happens.

A high voltage shock may punch through the skin layer and into the more conductive core.

JR
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Don't tune your drums half-ass. 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 #319 on: August 19, 2015, 06:52:47 pm »

I've thought about this a bunch and I don't know that the skin resistance is non-linear, but the human body is not a simple homogeneous resistor. Our core which is like a dilute salt water solution is pretty conductive. The skin layer is not a great conductor especially when dry, but rarely completely dry..

The crusty old electricians who show off by grabbing live wires have (dry) callused hands to protect them.

Another variable is how tightly you grip the conductor.. grabbing tighter will deliver lower resistance.

Since electricity follows the lowest impedance path, it doesn't travel from hand to hand just on your outside skin, but inside your body where the bad stuff happens.

A high voltage shock may punch through the skin layer and into the more conductive core.

JR

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
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Re: brain storm an optimal human safety system for back line
« Reply #319 on: August 19, 2015, 06:52:47 pm »


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