Static Electricity

[Pacetech]

I'm having an issue with static electricity, if I pick up my controller (which is 2 knobs with optical encoders + Plug A Pod) after shuffing my feet on the carpet, my encoder position resets. Its resetting because my quad timers are set up to re-zero the encoder every time it gets the INDEX pulse from the encoder. Now, Ideally I only need to index once so I can disable the reset after initialization.

The controller is connected to the base unit via a 5 pin cable (12V PWR, GND, CANL, CANH & GND). 12V power is regulated to 5V via a PT5101 switching regulator - to supply the POD and encoders.

The encoders A/B/Index are on a short 6" cable that connects directly to the POD inputs (no limiting resistors).

The shield of the cable is connected to the connector shells, all metal connectors and enclosures.

The base unit is another metal housing with 2 ISOPODs and a bunch of stuff. Main power in connected to the base unit via a 12V 10 amp-hr battery. They system is isolated from EARTH/Ground.

What is the best way to stop static electricity in my case?

[RMDumse]

Well, static is a bad thing and can easily kill electronics so be careful.

On the otherhand, it sounds like you are relying on the internal pull ups on the quadrature/timer lines. They are very weak. You might try "beefing" them up, putting a much smaller resistor in parallel with them. Try a 2.2K from each of quadrature/timer lines to the +3.3V rail. There's a good chance this would get you past your current problem.

[ngkdc]

I absolutely HATE static electricity.

Here's how I tackled it in my office:

Take a large refillable spray bottle and mix 1 part liquid fabric softener (my wife had "Snuggles" on hand) and 4 parts water.

Label the bottle

Shake the bottle well, and lightly spray your entire carpet with this mixture. If you can't stand the smell of your particular brand of fabric softener, realize the perfume dissipates in a day or two ... hit the rug before you go away for the weekend.

Respray the rug when you notice ANY static problems. I now treat my office rug about once a year and have eliminated the static issue.

***

Of course, there's a reason I had to do this ... blew an op-amp input stage on an ADC board (not New Micros) I was working on, and ended up fixing the static problem, the ADC board (surface mount) and THEN finishing up the project.


Hope this helps,

Rick

[alxx]

If that doesn't fix it you can always get
carpet with a metal mesh / wires woven in
like the ones used on most aircraft, then get the carpet connected to a good ground point.

Last I heard the carpet is about Aus $120 a square meter so around US$85 a square meter. Not cheap but end of static from carpet.

Cheaper option is a anti-static floor mat + deskmat and anti-static strap, all properly connected and grounded

[Pacetech]

Well, I'm developing the system in my office, but I really cannot do this to the final product being used around the world.

We have a system being used in Austin, TX in an indoors warehouse on a concrete floor. One day they were complaining about system resets after the system was working for 4 weeks.

For those 2 days, there was a low pressure system and the humidity dropped. They system is battery operated and I told them to go ahead and ground it. It helped.

Once the humidity rose, the problem went away, worked well since - that was about 4 weeks ago.

So what can I do to a portable battery powered POD that cannot be easily grounded? I guess I can isolate the pod from the metal enclosure. All my cables are shielded and the shields ground to the metal enclosure.

[RMDumse]

Did you try stronger pullups?

[alxx]

Conformal coat the pcbs ?

Use a sealed case, with batteries in a seperate compartment.

If it is static giving problems may be stronger pull ups and more decoupling caps.

If static is giving these problems how are you going to go with ESD testing ?
or EMC testing ?


http://www.atmel.com/dyn/resources/prod_documents/DOC1619.PDF
Its by atmel is quite good on emc considerations.

Motorola / freescale should have a similar doc

[Pacetech]

Well, I'm in board layout mode right now so I am adding pull-ups. I was trying so get any more ideas to implement in the PCBs.

The Atmel doc was helpful - thanks for that.

-Patrick

[blueeyedpop]

1) Stop shuffling your feet.
2) Get a wrist strap, GFI outlet, and grounded workmat.
3) Get a humidifier.
4) Get grounded floor mat.