We will need to place our analgoue board in a metal box. This can then be placed with the digital board in a plastic box. (See Nelo's picture below. Note the analgue board is boxed at the bottom).
Boxing is mentioned in the modular OpenEEG FAQ
http://openeeg.sourceforge.net/doc/faq.html
"Q: Why is putting both boards in the same metal box a safety issue?
A: It is because you need to let the power and output signals pass through the box wall somewhere. There you have to ensure that the connectors are isolated from the box, or you will end up connecting isolated ground to PC ground, which is a bad thing. Even if the connector housings are made of plastic, you risk lowering the isolation voltage.
It is possible to use a metal box, if you create wide enough gaps between the connectors and the metal wall. Problem is, you still end up with an outer surface connected to isolated ground, so it is safer to avoid the subject entirely.
It is recommended that you put the amplifier board in a metal box, which is in turn placed in a plastic box along with the digital board. Look here for an example."
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Shielded cable generally use an electrostatic shield such as copper foil. I am thinking we can provide additional shielding for our boards by maybe lining the outside of such a box with cooper foil, or just have the casing made out of copper or some comparable material. Any thoughts?
ReplyDeleteI have posted re. audio cable and have found hundreds of boxes (metal and plastic) at RS, Rapid and Farnell. Rapid are very fast at delivering (as their name suggests).
ReplyDeleteWe were very pleased though to get signals last night on our unshielded cables.