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G0TWN > TECH 28.01.05 12:19l 114 Lines 5627 Bytes #999 (0) @ WW
BID : 46237-GB7IMK
Read: GUEST OE7FMI
Subj: DIY UV EPROM Eraser
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7CIP<GB7IMK
Sent: 050128/1004Z @:GB7IMK.#43.GBR.EU #:46237 [Via TCP/IP] $:46237-GB7IMK
From: G0TWN@GB7IMK.#43.GBR.EU
To : TECH@WW
DIY UV EPROM Eraser for under 15ukp!
------------------------------------
I don't pronounce originality for this project as it has been on the internet
for some time. I have merely sourced readily available items within the UK.
* * * WARNING ! * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Short wave ultra-violet light is extremely dangerous and can cause permanent *
* damage to eyes and skin. Ultra-violet light sources must be completely screened *
* off when in use. If you are at all unsure about the safety implications, DO NOT *
* attempt any of the DIY solutions suggested here. I accept no responsibility for *
* any harm caused by this project. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Parts
-----
Ultraviolet Mini Lantern.
Maplin Electronics. http://www.maplin.co.uk/ (stock code ZC10L) 9.99ukp
Pond Sterilisation Germicidal Tube T5 4Watt 150.1mm
First Light. http://www.firstlightdirect.com/ (part no. G4T5) 4.50ukp
VHS cassette storage case (plastic) NOT transparent!
Sticky pads or velcro tape.
*Optional* 6Vdc supply =>500mA (most cheap universal type is suitable).
Overview
--------
EPROM packages have a transparent mica window which allows the chip to be erased
by exposure to short wave ultra-violet radiation. Commercial EPROM erasers which
perform this function are typically expensive. 50ukp to 60ukp for basic types at
the time of writing.
I outline here a much cheaper solution.
Building an EPROM Eraser
------------------------
The best solution is to build an EPROM eraser incorporating a short wave germicidal
UV tube as the source, with a cheap lantern providing the necessary
electronics. This type of tube is very dangerous and can't be used unscreened.
An enclosure is needed, plus a means of switching off/on the lantern without opening the box.
Maplin currently stock a hand-held UV Mini Lantern. Commonly used for security applications,
revealing UV inks and hidden security marks on banknotes and stamps. This will form
the basis of the project. It comes with a black filtered UV tube that is unsuitable for
erasing EPROMs, so a replacement is required. They operate from either two AA batteries or
a 6Vdc supply. Any cheap universal type is suitable.
The UV tube is a 4 watt germicidal UV tube, type G4T5, which is a direct replacement for the
original tube. A search for a supplier showed varying prices from 14ukp downwards!
I stumbled upon First Light, a light bulb and fluorescent tube retailer. These tubes
are used in manufactured UV EPROM erasers, as well as medical and aquatic sterilisation
equipment.
Having tested the lantern, remove the clear plastic lens. You will not be replacing it as
it is not suitable for use with the new tube. Now replace the tube. This can be removed by
gently twisting it 90 degrees and then pulling from the sockets. Once the tube is replaced
DO NOT operate the latern other than within an enclosure!
Now for the enclosure. A plastic VHS cassette storage case has suitable dimensions. Ensure
that you use an opaque, not transparent one! The lantern can simply be held within the case
by means of sticky pads or self-adhesive backed velcro tape. The latern can be supplied power
via its 3.5mm jack socket. A 10mm, or there abouts, hole will need to be made for the DC power
plug. Just ensure that this hole is *just* large enough for the plug, reducing the chance of
UV leakage.
Operation
---------
With the power supply turned off, open the case and ensure the latern's switch is set to the
tube 'on' symbol. Position EPROM/s against the tube, with the/their window/s facing it. Close
the case and then turn the supply on. DO remember to turn the supply off before opening the
enclosure. At all times.
As this device has *NO* safety precautions against being accidently opened, when in operation,
keep it away from children and pets! Stick a warning on the case, whatever. Take all precautions
against accidental exposure. Probably best not left unsupervised.
Erasure times
-------------
Initially a bit of trial and error is required to find the suitable erasure time. Over exposure
could lead to shortening the life span of the EPROM so it is best to work it out.
Ensure that the tube is kept clean. Dirt or smears may cause damage, shortening its life. Ensure
that the clear window on the EPROM is clean or it may not get correct exposure, increasing the time
required.
Initially try ten minutes, then test it is blank in your programmer. If not, keep increasing time by
five minutes until satisfactory. Add another five minutes to the total exposure time to give
yourself a guide time.
As the tube ages, the exposure time will need increasing. When the exposure time becomes too excessive,
it is time to either replace the EPROM or the tube.
Improvements
------------
A metal enclosure with a safety feature that the supply is cut to the latern when the enclosure is
opened. An added feature would be a switch off timer switch to control exposure time.
Given that I wanted a device for occasional hobby usage and the fact that without a switch off
timer, it had best not be left unattended, I opted for this budget solution.
Regards from David G0TWN
Sysop GB7IMK [44.131.160.241]
IP Co-ordinator North Buckinghamshire - Region 160
Ampr: g0twn@gb7imk.ampr.org
AX25: G0TWN@GB7IMK.#43.GBR.EU
Email: dhumble_at_taurus2_dot_plus_dot_com
Inet: http://www.gb7imk.co.uk/
Ampr: http://gb7imk.ampr.org/
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