Author Topic: Housing PCB:s in styrofoam and static electricity?  (Read 6147 times)

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Offline Fredrik AnderssonTopic starter

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Housing PCB:s in styrofoam and static electricity?
« on: December 30, 2007, 04:22:59 PM »
I'm planning for the housing of all electronics on our hexapod and want a neat artistic look on it. In fact, thats really important because our goal is to make an impressive robot, that will impress people that's not into robotics (a robot that looks ugly but has some cool programming doesn't really do it, trust me  :-\ ).

So i was thinking i would use styrofoam for the body, housing all the electronics in an enclosed body. However, when i tested working with it i noticed the small bits that it's made of where attracting to every kind of object. Aha! Static electricity!

How does this effect the electronics if i house them directly on the styrofoam? Could they be completely ruined by a chock of static electricity? If i painted the styrofoam with something non conductive, would that protect the electronics?
« Last Edit: December 30, 2007, 05:15:35 PM by Fredrik Andersson »
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Offline sdk32285

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #1 on: December 30, 2007, 08:04:16 PM »
You are correct Styrofoam is bad for electronics it can destroy your chips.

You can use plaster-of-paris or similar to build a shell that goes over the robot.
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Offline ed1380

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #2 on: December 30, 2007, 08:46:53 PM »
admins boat was made of styrafoam and had electronics inside
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Offline sdk32285

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #3 on: December 30, 2007, 09:13:36 PM »
Many distributors use styrofoam since it has a semi low chance of actually causing damage compared to the cost of packaging material. If you are using not as sensitive components you will probably be ok (this is not an endorsement to use styrofoam), however using CMOS/highly sensitive chips can cause you a bit of trouble.

As bell labs figured out (see below) styrofoam can be expensive and actually can cause problems.

A long long time ago, in a different generation, etc... Bell Labs decided to ship RAM chips using styrofoam. Many of their chips would arrive defective. After spending a lot of money they realized that it was their styrofoam packaging that was destroying their chips. As part of this they determined that a styrofoam cup with coffee in it still has the potential to destroy more chips than acceptable.
In addition to "discovering" properties of styrofoam they also created Fax machines, synchronous sound and video for TV, the solar cell, C programming (as a replacement for B), the transistor, TDMA/CDMA for cell phones, and a ton of other stuff. (wikipedia)
And they lived happily ever after with no styrofoam (actually they didn't, but that's another story)

« Last Edit: December 30, 2007, 09:24:27 PM by sdk32285 »
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Offline HDL_CinC_Dragon

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #4 on: December 30, 2007, 11:23:30 PM »
Dont suppose you could mimic a Coax cable and just shield your electronics? the FCC might not like it but who cares lol
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Offline paulstreats

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #5 on: December 31, 2007, 05:04:46 AM »
dont see why the fcc would mind, since shielding would prevent your device from creating interference. Just some type of meshcage around the electronics would do.
I had an indoor rc helicopter where the electronics were surrounded by a styrofoam body, this never had much problem (maybe you can get low conductive/ static styrofoam)

Offline Fredrik AnderssonTopic starter

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #6 on: December 31, 2007, 08:51:08 AM »
Thanks, this was extremely useful information for me. You just saved my project!

I know a ATmega168 i ordered was packaged with the pins sticked on to a piece of styrofoam although sdk32285 stated it's pretty common. I guess these chips are pretty sturdy though, but yeah, i should probably still watch out.

I was planning on using a sandwich like construction, first an aluminum bottom then a layer of styrofoam then a layer of some thin plastic material (not for improving the sturdiness, just because i need something that is possible to screw things onto), then again a layer of styrofoam and so on with the styrofoam layers beeing 2 cm each. So i don't really know how to solve it now. I can't really ditch styrofoam as the metal and plastic parts I've cut out is very thin and unrigid working just as a skeleton for the styrofoam. What about coating the styrofoam? Is there any kind of paint that would do the job? Is there a special kind of styrofoam or any material as rigid and light as styrofoam that does not give static electricity?
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Offline dunk

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #7 on: December 31, 2007, 10:58:06 AM »
so in my experience most of the components you will be working with making an AVR based project will be fairly robust when it comes to ESD damage.

if you ever start working with high density RAM chips then i'd stay away from styrofoam but for EEPROM based microcontrollers i seriously doubt if you will be unlucky enough to damage one by encasing the circuit in the stuff.

all my fried components over the years (and there have been lots) can be blamed on either short circuits or over voltage issues caused by my carelessness rather than static.

this is not to say ESD is not a serious issue in industry, particularly when dealing with new (and therefore delicate) technologies, where sensitive components can have their life expectancy dramatically reduced by careless handling.
thankfully most of the components we use building hobby robots have been designed to be versatile so they are manufactured to be resilient to all manners of damage to increase their range of possible uses.
it's always worth avoiding purchasing components advertised as "low voltage" versions of a standard part unless you actually need to run outside the specs of the standard part.


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Offline HDL_CinC_Dragon

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #8 on: January 01, 2008, 07:28:19 PM »
dont see why the fcc would mind, since shielding would prevent your device from creating interference

the FCC requires devices to accept interference so that if anyone ever created something, they could shut it down by interfering with its circuitry.

build the $50 robot then arm it with an explosive and put a mesh cage around the electronics to shield it. Now its a threat and cant just be EMPed to stop it since its protected from EMFs.... Thats why they would care :P
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Offline airman00

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #9 on: January 01, 2008, 08:27:35 PM »
dont see why the fcc would mind, since shielding would prevent your device from creating interference

the FCC requires devices to accept interference so that if anyone ever created something, they could shut it down by interfering with its circuitry.

build the $50 robot then arm it with an explosive and put a mesh cage around the electronics to shield it. Now its a threat and cant just be EMPed to stop it since its protected from EMFs.... Thats why they would care :P

LOL

I think the FCC doesn't trust us.. I wonder why ?  :D

( meanwhile I'll be putting a machine gun  on my robot butler and covering the robot in a mesh cage) no, jk
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Offline paulstreats

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #10 on: January 02, 2008, 07:11:29 AM »
I thought the whole deal with accepting interference was so it didnt disrupt radio and tv signals, since a herf gun could damage a mesh shielded bot(within reason).
The latest mobile phone that I scrapped was built with all of its chips fully enclosed by solid metal covers, thereby blocking any emf and herf.

(are they really silly enough to send emp's to an explosives trigger mechanism? or as a last resort when the explosive is moved to a safe place)
« Last Edit: January 02, 2008, 07:14:35 AM by paulstreats »

Offline HDL_CinC_Dragon

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #11 on: January 02, 2008, 04:45:08 PM »
Yeah cell phones do have certain circuits that are caged but the device as whole could still be disrupted by a strong enough EMF. Typically they wouldnt EMP an explosive device unless it was the absolute last resort. What they often do is shoot it with a very powerful water cannon or basically take a torch to the control mechanism lol. sit a block of thermite on top of the control circuit and ignite the thermite remotely.

Cell phones can still be interfered with quite easily. All you need to do is throw enough electricity into the air and the phone wont be able to get signals or anything of that nature but the main electronics will however still be ok unless a much larger EMP was detonated at close proximity. The military uses this principle to help protect their convoys and patrols. They have cell phone jammers equipped in some of the APCs and HMMWVs(Hummvees). That way, remote bombs and cell phone bombs cannot be detonated remotely.... however im sure they could just have a signal meter on them so that when the signal is lost completely it waits like 3 seconds and then detonates automatically :-\
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Offline ed1380

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #12 on: January 02, 2008, 05:27:30 PM »
or even easier. a long arse wire
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Offline paulstreats

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #13 on: January 02, 2008, 07:02:20 PM »
Quote
.... however im sure they could just have a signal meter on them so that when the signal is lost completely it waits like 3 seconds and then detonates automatically

or just write an easy java application with a built in timer.

Offline HDL_CinC_Dragon

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #14 on: January 02, 2008, 09:02:47 PM »
exactly.
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Offline Admin

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #15 on: January 20, 2008, 05:11:16 PM »
Quote
admins boat was made of styrafoam and had electronics inside
well, I painted over the styrofoam with acrylic, had a plastic HDPE layer, then the electronics were inside a plastic casing

An idea for you - you know those grey static protection baggies that all electronics come in? Use that to protect your electronics near your styrofoam. I always keep static bags around for this very reason.

ps - You guys definitely have issues staying on topic :P

Offline HDL_CinC_Dragon

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #16 on: January 20, 2008, 10:28:44 PM »
I ordered about 200 anti-static bags from I forget where but man its awesome :)

Im pretty sure you could also take a small wire netting(such as metal screen from an old screen door?) and make a complete bubble around your electronics so that the static will hit the bubble instead of the electronics... right?
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Offline Fredrik AnderssonTopic starter

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #17 on: March 18, 2008, 03:45:09 PM »
I needed to dig up this topic. I've been using a styrofoam casing for a whole now without encountering any problem. However, it does crumble a bit on edges and such, so i thought i would paint it with paint it with some coating that will keep the surface nice. I had a bottle of liquid latex at home so i painted it onto the styrofoam which gave it a much nicer surface.

Now i need to know if this maybe was a stupid act. I know that latex balloons can cause really much static electricity. Are that kind of latex i painted with the same as the balloon, and how will it have a worse affect on the electronics than the styrofoam?
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Offline bukowski

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #18 on: March 18, 2008, 03:58:02 PM »
I think that baloons pick up all that static electricity from friction causing the air inside it to become negatively charged. I dont think you will have much of a problem unless your robot happens to drag along a carpet for a bit.

Offline kd5kfl

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #19 on: March 18, 2008, 04:02:32 PM »
Quote
the FCC requires devices to accept interference so that if anyone ever created something, they could shut it down by interfering with its circuitry.

Not quite.

When the FCC says a device has to accept interference, that just means "Don't come crying to us when your cheap unshielded consumer electronics don't work next to a high powered transmitter." You can shield the electronics yourself and solve your own RFI problems; don't expect any assistance from the FCC.

Offline paulstreats

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Re: Housing PCB:s in styrofoam and static electricity?
« Reply #20 on: March 18, 2008, 06:03:50 PM »
I think the static charge builds up on the outer plane of the latex and not the inner plane where your electronics will be. Whatever, the static will only discharge to ground meaning that if it discharges into your electronics, it does this whenever the charge builds(trickles) up (because the gnd is always present in a powered circuit it absorbs the charge as it comes in rather than the charge building up over time) so you are not likely to get a massive spike from it. The most likely occurence is that it builds up on the outside of the latex where the friction etc caused it to and has to discharge to something that is also on the outside of it.

 


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