Unless you prevent them from touching the pins themselves, you can't do much. Even series or parallel resistors aren't going to help that much. Zeners and other surge suppression devices might help, but they're going to cost you. Here are some other ideas you might consider: Place a large, obvious ground trace around the perimeter of the board, unmasked with silkscreen, "TOUCH HERE FIRST". Place a similar unmasked ground guard around the processor. Socket the processor, and add a button (and software to implement the button's functionality) to the programming software: "VERIFY BOARD" which loads a program into the PIC and tests all possible functionality of the board and processor. Make sure it instructs the students to disconnect the board from anything else in case testing the I/O has unintended consequences. Perhaps make some sockets that plug into the headers to act as a loop-back device for testing the I/O. Skip all that and instead use a silicone conformal coat spray to coat the PCB. Use masking if you want to avoid coating contact points, buttons, knobs, etc. Add the recommended ESD protection to each user accessable pin (zener/resistor). http://www.ellsworth.com/display/productdetail.html?productid=1810 Use surface mount, mount everything to the bottom, and add a dollar's worth of standoffs, hardware, and a sheet of plastic. Mount the PCB onto the plastic so the electronic parts are not easily accessible. Ground pour on top. Make the assembly so cheap (ie, BBB arduino, for instance) that replacing the entire unit is a no-brainer and doesn't hit the pocketbook of the student too hard. Make sure there's an easy way to test whether it's functional or broken, as above. Use I/O driver chips that have the built in ESD protection. Socket them. Ground pour both sides, unmask the ground pour, and seperate tracks so that it's much more likely the fingers and other objects will contact ground before anything else. Keep in mind that static shocks will go through mask (IIRC, it only takes about 2-7kV to breach typical mask). Make little metal shields that cover the important bits with tabs that go through grounded, plated holes in the board and then twist, bend, or solder to hold in place. Add ESD protection on anything coming out from under the shied. Should be able to make them with tin snips, forming them on the edge of the desktop, or pretty cheaply by a metal shop with a turret punch and sheet metal bending form in small quantities. They may also be found as COTS items if you search and layout your board to match. Long lead time, but maybe emachineshop or http://www.ponoko.com/ can build something here inexpensively. http://www.ponoko.com/ might be able to make very cheap build it yourself enclosures. Redesign the board to fit into a common snack tin or box, and instruct students to install it into the appropriate housing to avoid having to buy replacements due to ESD failure. Install series and parallel resistors anyway to avoid overvoltage and short issues that are bound to cause similar undetectable issues. They won't provide much protection for ESD, but they're cheap and will solve a raft of other problems. Realize that the product is not suitable for the target market, bite the bullet, and use a case. Sell it without the case for cheaper, but with no (or a much more limited) warranty. Allow students with limited means to pay for their units by fixing and testing broken units. Um... I think that's it for this brainstorming session. -Adam On 2/16/08, wouter van ooijen wrote: > I use PICs in classes. The PICs are on a PCB, but otherwise unprotected. > The students buy the PCBs, so they can work at home. Informatics > students can not be expected to know much about static electricity, so > for all I know they might use it to comb their cat's hairs. I have hadd > some pretty weird failures previous years, so it might be a good idea to > put some form of protection on all PIC pins. My idea is a resistor to > ground for each pin, but what value? Would 1M be sufficient, or should > it be lower? > > And what about the one pins that probably won't like any load, even 1M: > the oscillator input? > > Wouter van Ooijen > > -- ------------------------------------------- > Van Ooijen Technische Informatica: www.voti.nl > consultancy, development, PICmicro products > docent Hogeschool van Utrecht: www.voti.nl/hvu > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist