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The Jaycar “UV Anti-bacterial Cleaner” kills germs on toothbrushes and shavers and with a small modification can also erase EPROMs. A 1000mF capacitor is connected in parallel with the onboard 220mF capacitor, extending tube run time from a few minutes per session to over 15 minutes. Due to space restrictions, the capacitor is connected to the PC board with flying leads, which are fashioned from light-duty hook-up wire. It can then be held in place with hot melt glue or non-acetic silicone sealant. A cheap UV EPROM eraser A recent gimmick in toothbrush holders proves to be just the ticket for erasing EPROM-based ICs. One additional capacitor and five minutes of work are all that’s required to perform the transformation . . . and you can still use it to sterilise your toothbrush! By BARRY HUBBLE Not too long ago, enthusiasts developing microprocessor-based projects needed access to an ultra-violet (UV) eraser. Unlike current technology devices that can be electrically erased in seconds without even removing them from circuit, older EPROM-based devices have to be exposed to ultra-violet 80  Silicon Chip light to erase their contents. With the advent of electrically erasable memories (EEPROMs), the requirement for a UV eraser has gone by the wayside and it is unlikely that most hobbyists will have one in their kit. However, if you need to modify or repair older equipment that uses EPROMS or want to dabble with any of the microcontrollers that use EPROMbased program memory (such as the PIC16C745/65), then an eraser is still a “must have” item. Dedicated UV erasers are available but at around $300 or more, they would be considered too expensive by most experimenters. Even homebuilt units could prove expensive with tubes costing around $70. Of course, exposure to sunlight for a week or so may erase the chip but don’t hold your breath! A cost-effective solution lies in the Jaycar GH1507 toothbrush holder ($24.95). In its intended use, the UV light from the fluorescent tube in this product kills germs in your toothbrushes and shavers. As luck would siliconchip.com.au Tektronix TPS2000 The New Isolated Channel Battery Operated Scope. Here’s a close-up of the rear of the board showing the two connection points. In this example, the black (bottom) wire goes to the negative capacitor terminal. have it, the light spectrum used for germ eradication also works well for erasing EPROMs. Modifications Whenever the door of the toothbrush holder is closed, it closes a switch, turning on the tube and starting a timer. After a few minutes, the tube is automatically switched off. All that’s required is a modification to the timing circuit to extend the operating time of the tube to something more suitable for EPROM erasure. In its simplest form, the modification consists of adding a 1000mF capacitor in parallel with the existing 220mF capacitor in the timing circuit. This larger total capacitance gives an exposure time of about 15-20 minutes. I have erased four chips at a time with this exposure and have encountered no problems. However, due to the spread of the lamp specifications (0.75 - 1.5mW/cm2), it may be necessary to alter the value of capacitance by trial and error to achieve reliable erasure. To modify the unit, carefully remove the rear cover and identify the 220mF timing capacitor (the largest The existing toothbrush rack is easily removed, allowing up to four EPROMs to be erased at a time. Do you face these Power Measurement Challenges? • Make multi-channel floating measurements • Measure current and voltage distortion and their spectral content • Measure harmonics, instantaneous power, power factor, switching loss to characterise power electronics circuitry • Measure 3-phase currents & voltages • Validate compliance to regulatory standards • Work in an environment without AC Power • Document and Save your measurement results For more information about the TPS2000 family... Talk to NewTek Instruments: Ph: 02 9888 0100 email: info<at>newtekinstruments.com NewTek Instruments Pty Ltd - Sydney - Melbourne www.newtekinstruments.com siliconchip.com.au March 2005  81 Fig.1: a simple IC carrier can be made up from a piece of scrap plastic and some wooden dowels if the unit is to be wall-mounted. You will also need to affix a strip of conductive (anti-static) foam to the opposite side of the plastic to hold the EPROMs in place – see photos below. one). Solder a 1000mF 25V electrolytic capacitor in parallel with this capacitor, ensuring that the correct polarity is observed. Due to lack of space to add the capacitor directly, it should be attached with flying leads and secured with hot melt glue or similar in a position where it doesn’t foul the case. Before screwing on the cover, double check the polarity! Warning: never operate the unit in a disassembled condition or without the plastic door fully closed. The UV rays produced by this type of tube could damage your eyesight! Scottish special? With a little planning, the cost of this project may well be less than a dollar (for the capacitor). How? Well, consider the possibilities were you to give your spouse or friend a toothbrush holder for his/her birthday. Then using our special IC carrier, you can substitute your EPROMs for the usual line-up of toothbrushes when he or she is out mowing the lawn! Perfect! All jokes aside, the unit can easily do both jobs with a couple of simple additions. First, a switch can be inserted in series with the 1000mF capacitor, allowing it to be switched out of circuit for toothbrush cleaning duty. This helps to maximise battery life. Second, a clip-in IC carrier can be installed to allow the unit to operate in its normal position (on a wall). In this case, the chips must be aligned length-ways on the carrier to prevent fouling the toothbrush rack. The carrier can be fashioned out of scrap materials and is held in place by the toothbrush rack. I used a piece of 2.5mm thick plastic from a jiffy box cut to the dimensions shown, with some 9mm dowel off-cuts held in place by 4g x 12mm countersunk screws. A piece of conductive foam is then glued to the face. Power If used frequently, you may wish to dispense with the batteries and power the unit from a 9V DC plugpack. We found that maximum light output occurs at about 8.5V input, so if using a multi-voltage plugpack, try one of the lower settings. We found that the “6V” position on our 1A plugpack produced 9.2V when supplying the modest (110mA) current demands of the holder. A 1N4004 diode is series with the supply brought this back to the desired 8.5V. SC ABOVE: the EPROMs to be erased are attached to the holder simply by pushing them into the conductive foam. RIGHT: the IC holder is then clipped into place in the toothbrush holder with the EPROMs facing down, ready for erasing. Note that the lid must be closed for the unit to operate. 82  Silicon Chip siliconchip.com.au