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Adam-Taylor
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Before you apply power
Adam-Taylor   7/18/2014 2:29:07 PM
Max,

As I am used to powering up space boards stuffed with components which cost millions of dollars, one thing I like to do first is check the polarity of components and the pin one allocations. Along with the correct devices being fitted.

I also like to measure the impedance between power and ground rails to ensure there is no direct short alothough with modern high power FPGA this can still be a low value. Then thre is the first application of power at a low voltage 0.5 v ish with a low current limit to ensure if it does trip out there is not much power 

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Max The Magnificent
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Re: Before you apply power
Max The Magnificent   7/18/2014 2:33:32 PM
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@Adam: ...one thing I like to do first is check the polarity of components and the pin one allocations...

Good point -- in fact, even though I had only two ICs, I did check that the "notch" on each was pointing to the left (thereby indicating pin 1 was where it was supposed to be :-)

Crusty1
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CEO
Re: Before you apply power
Crusty1   7/18/2014 3:26:09 PM
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Hi Max, Three ways I link to solid ground is to use the scope ground, the soldering Iron, wont buy a soldering station without a ground socket for a strap, and finally a modified wall socket plug with an earth clip mounted to the outside of it.

And yes I can always forget to use it.

Garcia-Lasheras
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Re: Before you apply power
Garcia-Lasheras   7/19/2014 6:45:27 AM
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@Max: Have you thought in buying one of those dissipative rubber mats for your desktop? In addition to solving ESD issues, they also protect your workbench table of being burned with your soldering iron.


I'm looking for a convenient unit for my own home-lab, so if I find a cool offer I will send you the reference (3M has a very good range of products, and you can buy one directly from online stores such as Digikey).

mhrackin
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CEO
Grounding
mhrackin   7/21/2014 12:43:38 PM
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It turns out that the standard banana plug is a pretty good fit in the standard US U-ground outlet. Most ground straps I see (and the grounding leads of the anti-static mats mentioned above by Garcia-Lasheras) come with a nice black banana plug AND an alligator clip that the banana plug can be plugged into.  The better ones have stacking banana plugs so you can plug both the anti-static mat and the wrist strap into a solid ground.  The alligator clip method is perfect for working on PCs with a metal chassis but not very good for a breadboard!

Added comment: that standard banana plug is a BIT loose, but it's easy to expand the diameter: a 4-way split (common) one will accept taking a small flat-blade screwdriver (the kind every engineer has several "giveaway" ones) under each leaf to expand the effective diameter.  Even the old/cheap plin solid pin versions can be modified with a similar surgery.

 

mhrackin
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Re: Before you apply power
mhrackin   7/21/2014 2:13:11 PM
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The going rate @1 for most of these is US $11 per square foot for ready-made ones including the grounding point and grounding wire. Typically they have 2 grounding points to allow daisy-chaining of adjacent benches, or attachment of a wrist strap.  I've bought several of these for my lab benches at work. My only beef with them is the grounding conductor attachment sticks up from the surface over 1/2 inch so you can't put any equipment in that area.

elizabethsimon
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CEO
Re: Before you apply power
elizabethsimon   7/21/2014 4:37:21 PM
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I've got a couple of large anti-static mats on my workbench as well as a couple smaller ones that were designed to be used as keyboard mats. The grounding points on these mats have a socket for the ground strap and a wire with a ring terminal. The ring terminal is supposed to attach to the grounded screw between the outlets on a standard duplex wall outlet.

This works well if you have a permanent workbench but it's not practical if you happen to be using a dining table or some such that has to be cleared off when you're done. On the other hand, using the mat to protect the surface of said table is a good idea. What I'd suggest doing in that case is to ground the mat to the power strip that you will be using to power your equipment.

By the way, the surface of the anti-static mat and the wrist strap are NOT shorted to ground but have some resistance that is sufficient to dissipate the static charge without shocking you.

 

Garcia-Lasheras
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Re: Before you apply power
Garcia-Lasheras   7/21/2014 4:47:58 PM
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@elizabethsimon: "the surface of the anti-static mat and the wrist strap are NOT shorted to ground but have some resistance that is sufficient to dissipate the static charge without shocking you."

As far as I remember, my ankle anti-static band is labeled as 1 Mega Ohm between the strap in contact with the skin and the part that touches the floor -- of course, this is useless unless you are on a special dissipative floor such as the one in SMD facilities.

Crusty1
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CEO
Re: Before you apply power
Crusty1   7/22/2014 3:26:24 AM
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@all, This topic brings me onto! which power supply should I decide to use before I liven up my board?

Do I use the big dual linear power supply, very stable and takes up a lot of my small bench, or do I use the little wall socket, switch mode brick.

After getting one hell of a tingle from the Wall brick via the low volatage side last night I am just begining to think that whilst the wall bricks are usefull I would rather not get that tingle.

Why is it that switch mode supplys seem to generate these tingles, I had a co worker who was leathal to work with, as she always disconnected the ground pin from her scope supply and it always seemed to be me that caught a tingle, so much so, that I ended up wearing insulated gloves when I worked in her lab.

 

David Ashton
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Re: Before you apply power
David Ashton   7/22/2014 5:03:32 AM
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@Crusty - in addition to giving you tingles, the wall brick will have no or fixed (high) current limiting.   Just in case you make a wrong connection which will cause you to lose the magic smoke in your new board, use your lab power supply and set the current limit to one which will only just supply the board under normal conditions, or even a bit less.  Much safer way to go.  Once you know it's all working, change to the wall wart if you are brave... :-)

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