How do you protect your sensitive equipment from tc interference? / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

How do you protect your sensitive equipment from tc interference?

previous 1 2 3

Move Thread

LAN_403

2Spoons

Sun Jun 24 2012, 10:35PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

I'm betting the anti static bag will be useless because the conductive layer will be too thin and too resistive to form any kind of shield. Your shield should ideally be a couple of skin depths thick - and any holes or slots less than 1/20 of a wavelength (not really a problem in 200 kHz region). Steel, or better still silver plated steel would be your friend here. I think even ITO glass would not be up to the task.

Ben Solon

Sun Jun 24 2012, 10:43PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

PhilGood wrote ...

ben123324 wrote ...

PhilGood wrote ...

...Whe need to find some conductive but transparent and flexible material. What about these antistatic plastic bags used for sensitive components ?

Catch-22... 2? A capacitive touch screen sensed the em field of your finger it's not pressure sensing or resistive, so any kind of em shielding in between you and the screen doesn't allow you to use the screen. No matter how clear or flexible...

Well it works, probly because when you push the conductive film towards the screen, it changes the capacitance of that screen area.

Unfortunately I couldn't check if it effectively protects the phone from e-fields, my only TC was not ready to run, I'll try that later.

Now if it works, for a reliable operation, it requires that the antistatic film is tight close to the screen but without touching it, ~2mm seems fine, could be done with a sipmle plastic frame having the size of the screen.

Actually, the screen is sensing your field through the layer of plastic or glass or whatever. Not the pressure. Its called capacitive touch because you are capacitivly coupled to the screen through the plastic. The plastic acts as a dielectric. So it still works capacitivly with that. Once you put em shielding on that though, all bets are off.

Ash Small

Sun Jun 24 2012, 11:36PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

ben123324 wrote ...

Actually, the screen is sensing your field through the layer of plastic or glass or whatever. Not the pressure. Its called capacitive touch because you are capacitivly coupled to the screen through the plastic. The plastic acts as a dielectric. So it still works capacitivly with that. Once you put em shielding on that though, all bets are off.

Are you sure? I have an HTC touchscreen phone, and it tends to work better if you 'tap' the screen with a fingernail, rather than just touching it, which doesn't always work. Maybe not all HTC screens operate in the same way, I don't know.

(Mine is badged as a 'Vodafone 451', I think, and is about three years old.)

I've never used mine in an EM field, as my Fuji digital camera produces much better photos.

PhilGood

Mon Jun 25 2012, 12:39AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

ben123324 wrote ...

PhilGood wrote ...

ben123324 wrote ...

PhilGood wrote ...

...Whe need to find some conductive but transparent and flexible material. What about these antistatic plastic bags used for sensitive components ?

Well it works, probly because when you push the conductive film towards the screen, it changes the capacitance of that screen area.

Well, if you have a better look at my video, you will notice I'm using a wooden pencil (gum end) to press the antistatic film towards the touchscreen.

I used a pencil on purpose to show that finger is not involved in touchscreen reaction.

The plastic I use is antistatic metallised shielding bag like this

,or.r_gc.r_pw.r_qf.,cf.osb&biw=1317&bih=749&pdl=300&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=e6vnT-2xMtSe8gORp-zZCg#um=1&hl=fr&tbm=isch&sa=1&q=antistatic+metallic+shielding+bag&oq=antistatic+metallic+shielding+bag&aq=f&aqi=&aql=&gs_l=img.3...19464.32294.0.32636.5.3.0.2.0.0.212.594.0j1j2.3.0...0.0.eO0lC1zx57U&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=1a1aed0a520c91ca&biw=1317&bih=749 ,there is no need to put anything else above it.

I couldn't try with my TC today, but I hope it will be enough to protect the phone from TC's e-field.

Now if you still have a doubt, I did the same but without the antistatic film, and the touchscreen doesn't reacts ... explain :p

@Ash Small : a three years old phone might have a resistive touchscreen, that works with pressure. Capacitive touchscreeen became common 2~3 years ago depending on the brands.

hsieh

Mon Jun 25 2012, 06:10AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

Today I take pictures of my SSTC with my friend's hTC sensation.Nothing goes wrong.The distance between the cell phone and my SSTC is about 1.5 meter.

PhilGood

Wed Jun 27 2012, 09:18AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

This morning I reassembled my TC and a quick test proved that the antistatic film fulfills its role as I expected.

So I built something neater :

DIY : smartphone easy shielding soft case

- a piece of transparent metalized antistatic film

- a frame made of Ã˜ 2mm copper wire sheathed with heat shrink. (It could be anything else as long as it is the size of the phone and ~3mm high. It must be smooth to avoid scratching the screen). Paste it on the film with cyanoacrylate glue.

- an aperture for the camera. (I put copper tape around the camera hole to catch sparks that might hit the camera lens. I am not sure at all it helps, but it doesn't hurts to try)

- adhesive tape to keep the whole thing tight around the phone. (It must be tight enough to allow the phone to slide in forcing slightly)

I took these pics at less than 10cm from the break out point, with some streamers occasionally hitting my hand / the phone.

The phone isn't showing any sign of interference from the e-field.

Without the antistatic film I could hardly take a pic at less than 1.50 meter from the coil.

Thanks Destroyer for starting this thread !

previous 1 2 3

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob