Hi Eric et. al., > dlions@acs.itd.uts.edu.au wrote: > > > Has anyone considered using arc welders as a source of strong UV > > to erase eproms. I don't mean a full 50kg arc welder, but using the same > > concept of the spark it produces, and the UV from it. > > I think that in the long run your welding rods will be more expensive than the > UV eraser. I'm still searching for one of those lights thay use at the bank to > check the money for forgery.... should be cheapish. > > Wheter its safe? If you protect your eyes and don't stick your fingers into > the arc, I'd say its reasonably safe! The UV you get from the money checkers is rather soft UV at low intensity, it will take a long time to erase with one of those lamps and they are pretty much eye-safe. They are also used by philatelists for checking inks on postmarks. This is the same type of UV that you would have in a disco UV lamp, it is a tube made of glass (not fused quartz) and has a blue phosphor on the inside that translates the hard UV to something safer. Places to get hard UV lights include the following : Minerologists UV lamps (usually have both types of tubes) Dye penertrant testing units (often have both types of lamps) Flash lamps (should be a fused quarts tube for best effect) as used by semiconductor manufacturers and in the early Parallax trueflight in circuit downloader for the 16C71 and in one of those eraser guns (EPROM in 15 seconds) that used to be advertised for lots of money in the trade magazines. Water sterilisers UV curing of inks and glues in printing and manufacturing industries Exposure tables for various photo resist systems. Any Arc lamp All of the above listed sources that are HARD uv are very bad for the eyes and will give you arc-eyes on 1 to 100 seconds, don't look at them for fun, a standard UV eraser OBVIOUSLY falls into the same category. As for using A DIY arc for erasing, you can buy what are known as 'gouging rods' for arc welders that are a coper plated carbon rod about 6 mm (1/4") diameter and 250 mm (10") long that work well, they last longer than a welding rod, generate no slag and only a small amount of copper vapour and can be used on the lowest setting of most home welders. The heat (IR) and visible light are also intense and the UV is significant. 10 seconds at 300 mm (12") should be enough for most ICs. Avoiding Electromagnetic damage could be a problem but having the chip in some static foam would help. Placing a metal screen in between such as from a microwave oven would help a lot (with the neighbours TVs as well) and getting a dicroic reflector optimised for UV would allow you to locate the chip still further. A UV optimised light pipe would be best. You will need to use aggressive forced air cooling of the arc chamber, rather design your own powersupply (read up about welders in your nearby university library) or get a book on oldies lighting systems and see how they regulate arc size with automatic solenoids. The arc has NEGATIVE resistance (like a LASER tube) so you need a current source but you need quite a high striking voltage of something to briefly touch the electrodes together. IF you use DC one electrode will wear out much faster but you could reverse the polarity on each strike depending on the average DC under PIC control to consume the rods evenly. AC is easier to current limit in mass broduces products (leaky inductor) but may be harder for the experimenter. You need about 90V (leathal) to strike a dry arc which will then reduce to about 20V that you have to current limit to less than 40A for the gouging rods, 4A will give you plenty of UV and hardly wear out the rods but hard to get out or a standard welding machine. Summary : Go buy an eraser. Cheers -- Kalle Pihlajasaari kalle@ip.co.za http://www.ip.co.za/ip Interface Products P O Box 15775, DOORNFONTEIN, 2028, South Africa + 27 (11) 402-7750 Fax: 402-7751 http://www.ip.co.za/people/kalle DonTronics, Silicon Studio and Wirz Electronics uP Product Dealer