DIY EPROM Eraser - for about £15

[Kat Manton]

Hi,

An EPROM eraser is little more than a UV-C tube in a box. OK, proper ones have a little drawer to put the EPROMs in, a timer, and an interlock to turn the light off when the drawer's open.

But I can time things myself and ought to be able to remember not to expose myself to UV-C.

UV-C tubes seem to be a bit expensive, until you discover they're used inside pond pumps for killing algae and can be found at aquatic/pet/garden supplies shops.

UV-C tubes are just flourescent tubes without the flourescent coating, so anything that'll run a regular tube will run a UV-C tube. Like, say, a cheap battery-operated flourescent torch.

So, here's what I used:

• Flourescent mini lantern (£4.99 from Maplin.)
• UV-C tube (£5.99 from Pet & Garden World, Leeds.)
• Storage box with lid (£2.99 from Staples.)
• Cardboard (Stuff keeps arriving inside it, effectively free.)
• Anti-static foam (Had some anyway, effectively free.)
• 6V DC 'wall wart' (Got several anyway, effectively free.)

That comes to £13.97 (I made this a while ago so prices may have changed, but I'd be surprised if they've changed a lot.)

First, I removed the clear cover from the torch and removed the original tube. Removing the cover gave me an idea about how to support the torch without modifying it or just using the 'innards'.

I took a few measurements and sketched out a few rough drawings on the back of an envelope. It's all been cunningly arranged to support the UV-C tube about 5mm above the top of an EPROM stuck in anti-static foam.

Two pieces of card were cut to be a snug fit inside the box. A slot is cut in one that's large enough for the torch to fit through. A smaller slot is cut in the other piece so just the tube-holder parts of the torch fit through.

With everything torch-related finished I fitted the UV-C tube.



Next, four pieces of card were cut to fit vertically inside the box, to form a ledge to support the 'shelf' made above. Another piece of card was cut to hold these in place, with a hole in it to take the anti-static foam.



And that's it. One DIY EPROM eraser for significantly less than the cost of a new commercially-made one.



I leave the switch on the torch in the 'on' position and connect/disconnect power externally with the whole thing assembled and the lid on. The lid is a loose enough fit to go on with the power cable draped over the edge of the box. There are enough overlapping bits of card for it to be light-tight.

I leave EPROMs in there for about 5 minutes then test them with the 'blank check' feature of my programmer. Usually they're cooked to perfection, the odd one might need a bit longer

Regards, Kat

[Paul Stenning]

That's a very neat job Kat.

[GMB]

It's good that there is a mass-market use for UV-C tubes to drive the prices down. They are not just tubes without phosphor, but are made of quartz instead of glass - which made them more expensive.

I would just add some points about erasing EPROMs:

It's important that they are properly erased. When checking for erasure you must be sure that the reader is checking them in the "program verify" mode which is not the same as just reading them to see if they are blank. If you don't know then stick a meter on the Vpp pin to see that it is using high voltage when reading the chip.

It's probably better to erase them until they are blank - then go another 50-100% to make sure, but don't cook them for ages as that doesn't help their life.

When making an eraser it's important to make sure that the EPROM window is evenly illuminated. It might be an idea to check that with an normal tube fitted. It's the reason for the little draws etc. on the professional ones - to make sure they are always positioned optimally.

Finally, don't be surprised if a different make/type of chip takes a different time to erase. They do vary quite a bit.

[quadtech]

A link which may be of interest -

http://www.romanblack.com/tube4w.htm

[XTC]

I always like to see something useful and generally expensive, ingeniously made from thrown away or cheap materials.

One worth remembering.

Well done Kat.

Pete.

[Kat Manton]

Hi,

Originally Posted by GMB

When checking for erasure you must be sure that the reader is checking them in the "program verify" mode which is not the same as just reading them to see if they are blank. If you don't know then stick a meter on the Vpp pin to see that it is using high voltage when reading the chip.

Thanks, I'll check that. I have an old Stag PP41 which has a specific 'Empty Check' function; I'd hope that a company like Stag managed to 'do the right thing' but I guess it's worth waving a meter at it to be sure.

Originally Posted by GMB

It's probably better to erase them until they are blank - then go another 50-100% to make sure, but don't cook them for ages as that doesn't help their life.

That's pretty much what I do; if the 'Empty Check' says it's done, it goes back in for a bit longer just to be sure.

Originally Posted by GMB

When making an eraser it's important to make sure that the EPROM window is evenly illuminated. It might be an idea to check that with an normal tube fitted.

Everything was measured up, designed and cut accurately; it may just be bits of cardboard but it's precision-engineered cardboard!

The tube's positioned along the centre-line of the box; the centre-line markings on the card in the bottom of the box remain. So I just stick the EPROMs in with the windows lined up with the centre-line marks.

It all seems to work and it's not being used commercially; just for my own projects. So it doesn't matter so much if something goes wrong. It's good enough for 'hobby' use IMO.

I considered using a mains-powered fitting/lamp of some sort. As I hadn't initially worked out whether I'd be using any fitting/lamp complete/unmodified or removing the 'innards' for mounting I decided to go with the 6V DC powered torch. If I'd used a mains-powered fitting, I wouldn't have assembled it in a card box using bits of corrugated cardboard; it would've probably cost more and taken longer to make.

As it happens, nothing has been modified; I've just changed the tube and left the tube cover off (and kept that and the original tube in the box the torch came in.)

This was an exercise in minimising the cost, time and effort in producing a functioning EPROM eraser, rather than producing a professional/commercial quality item. As such, I think it's a success. I could make a 'better' one; in a pretty box, with a timer, drawer, mains-power, interlocks... but for 'hobby' use, this is sufficient. I'd rather put money/time/effort into the things the EPROMs go in..!

If anyone fancies trying something similar, identify the original tube type then swap the 'F' for a 'G' to get the UV-C ('Germicidal') version of the same tube. In this case I replaced 'F4T5' with 'G4T5'. (See Wikipedia entries 'Flourescent Lamp - Tube Designations' and 'Germicidal Lamp' for more info.)

Cheers, Kat

[swordholder]

HI Guys,
A little off topic, but can these tubes be used for developing photo etch PCBs?

Mike

[XTC]

Originally Posted by swordholder

HI Guys,
A little off topic, but can these tubes be used for developing photo etch PCBs?

Maybe, but I've never seen it done. The photo etch systems work very well with the more common and safer blacklight type tubes, so you might have some debugging to do. I can't really see the point.

If you want to develop PCBs and erase EPROMs, you may as well have two small units for doing different jobs. My PCB exposure unit consists of a 12" blacklight tube fitting into a piece of plastic guttering with wooden ends. The tube was bought a long time ago with fittings,ballast and starter for about a tenner. I time it manually. For bigger boards than about postcard size, I'd have to think about using more than one tube and a different enclosure.

Pete.

[Joefarr]

You can also use UV LED's for PCB exposure; great if you don't want to play with mains voltages.

There's an article here:
http://www.techbites.com/20090923572...sure-unit.html


Regards,
Joe

[swordholder]

Joe,
Thanks for that link, will save for future reference

Regards
Mike

[DAVEHALL]

Great idea - I've been playing with a maplin 8w tube on & off for years -problem has been finding ballast to stop tube being over run -virtually given up on that idea . Next queery - what to use for the transparency to print it on a laser printer ?

[dominicbeesley]

I UV LEDs would work I've built one I mentioned in another thread: http://vintage-radio.net/forum/showt...&highlight=led

However Kat's idea is definitely cheaper! I would have gone that way if I'd thought of going to the pet shop or garden centre.

However for PCB work the LED has a marked advantage, as it is effectively a point source with a very even coverage over its "footprint" it gives sharper images -even when the negative is not in perfect contact with the PCB. I sent a friend a copy of a circuit I'd produced perfectly but on his lamp exposer we had to thicken all the traces and pads to get it to work.

I'll have to get hold of some eeproms!

Dom

[ppppenguin]

Maybe I'm mistaken but UV LEDs are about 350nm while germicidal UV tubes are about 280nm. 350nm may be OK for PCB work but they are not going to erase EPROMs very well.

[dominicbeesley]

Mmm, looks like you're right. They're not even 350nm but 400 mostly so no good...

Dom

[XTC]

Originally Posted by DAVEHALL

Next queery - what to use for the transparency to print it on a laser printer ?

I'm just gearing up to produce PCB transparencies with a mono laser printer. I've got film and tracing paper to try. From what I've read, apart from the cost, film crinkles slightly with the heat. Tracing paper is better and transparent enough to UV, but you have to experiment to get the exposure right.

A few years back, I used film with an inkjet and that worked fine.

Pete.


.

[dominicbeesley]

The people at http://www.craftycomputerpaper.co.uk/ were very helpful I got some inket slip-transfers (for logos) and "roughened" transparencies for ink-jet PCBing - both worked a treat.

They don't list laser transparencies but its probably worth seding them an email asking for advice.

Dom