Emc issues for electronics housed in a plastic box

[IanM]

Hello,

I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
connector at the top, 2 push button switches and user changeable alkaline AA
batteries. This is all going in a plastic enclosure. I am concerned about
the ESD part of the CE marking process and wondered if anyone had any
experience in this area and advice to offer.

The cct detects the presence of the USB and steals power from it and nothing
else (ie no connection to the data lines), it also communicates with rs232
equipment. So the cct is basically power supply, small microcontroller and
rs232 interface.

Thanks,

IanM

 

[Gibbo]

Hello,

I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
connector at the top, 2 push button switches and user changeable alkaline AA
batteries. This is all going in a plastic enclosure. I am concerned about
the ESD part of the CE marking process and wondered if anyone had any
experience in this area and advice to offer.

The cct detects the presence of the USB and steals power from it and nothing
else (ie no connection to the data lines), it also communicates with rs232
equipment. So the cct is basically power supply, small microcontroller and
rs232 interface.

Thanks,

IanM

Stick a CE mark on it. Copy someone else's declaration of conformity.
That's what everyone else does. You'll be fine.

Unless you're making a *really* screwed up circuit or a transmitter of
some sort, the chances are it would pass tests anyway. And nobody
bothers checking.

This opinion is both true and worth what you paid for it.

 

[Paul Mathews]

Hello,

I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
connector at the top, 2 push button switches and user changeable alkaline AA
batteries. This is all going in a plastic enclosure. I am concerned about
the ESD part of the CE marking process and wondered if anyone had any
experience in this area and advice to offer.

The cct detects the presence of the USB and steals power from it and nothing
else (ie no connection to the data lines), it also communicates with rs232
equipment. So the cct is basically power supply, small microcontroller and
rs232 interface.

Thanks,

IanM

Search for a thread a few weeks old which covers the basics of ESD
protection. The thriving business in compliance engineering and
independent test labs suggests that the poster who claims that no one
is really making efforts to comply is exaggerating, although I agree
that many products don't comply.
Paul Mathews

 

[Robert Baer]

Hello,

I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
connector at the top, 2 push button switches and user changeable alkaline AA
batteries. This is all going in a plastic enclosure. I am concerned about
the ESD part of the CE marking process and wondered if anyone had any
experience in this area and advice to offer.

The cct detects the presence of the USB and steals power from it and nothing
else (ie no connection to the data lines), it also communicates with rs232
equipment. So the cct is basically power supply, small microcontroller and
rs232 interface.

Thanks,

IanM

There are some (expensive) conductive plastic boxes available,
usually "available in any color you want, so long as it is black".
Or, if for production quantities, have them coated inside with
Acheson electrodag or equivalent; they have one or two that are not only
conductive but also dissipative (Nickel Carbonyl if i remember correctly).
Lastly, for onesies, line the inside with aluminum foil from the
kitchen, or conductive copper sticky tape (either the 3M crinkled "RFI"
finish or the plain flat stuff sold to get rid of garden slugs).

 

[Mike Harrison]

Hello,

I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
connector at the top, 2 push button switches and user changeable alkaline AA
batteries. This is all going in a plastic enclosure. I am concerned about
the ESD part of the CE marking process and wondered if anyone had any
experience in this area and advice to offer.

The cct detects the presence of the USB and steals power from it and nothing
else (ie no connection to the data lines), it also communicates with rs232
equipment. So the cct is basically power supply, small microcontroller and
rs232 interface.

Make sure the MCU is well decoupled, the power supply is current limited ( to avoid latchup
problems) and make sure you use the watchdog - this should give reasonable protection against ESD.
About the only major risk is when the connectors get plugged in - make sure all the shells are well
bonded together, and tracked in such a way as to avoid coupling transient currents into your
circuit.

 

[[email protected]]

About the only major risk is when the connectors get plugged in - make sure all the shells are well

bonded together, and tracked in such a way as to avoid coupling transient currents into your
circuit.

If you do this by bonding the ground contacts of all connectors onto a
ground plane covering most of the board area you will also greatly
reduce rf emissions.

John

 

[IanM]

Thanks for all the replies, I have got a lot to go on this morning!

regards

IanM