E PROM ERASER







A. PREFACE


An EPROM can be reprogrammed if we erased the data. How do the erase work ?
EPROM can be erased used an ultraviolet light. Usually EPROM being erased by used a specific ultraviolet lamp. This lamp has a wave-length about 2537 Angstrom or less than 400 nm. Even with sun light or neon light can erased EPROM, it is the reason why an EPROM must cover its quartz crystal window with an opaque label. Research showed that a 2716 type should be erased after 3 years by exposured with neon light continuously. With sun light, it's about one week.
The best way to erased EPROM is by exposure the crystal window with 253.7 nm ultraviolet light and intensity 12 mW/m2. The window has a distance about 2 to 3 cm. The exposure must apply as long as about 10 to 40 minutes (usually 15 to 20 minutes is enough).
What is the philosophy of erased an EPROM ?
The philosophy is that when we erased an EPROM, we make the data stored in it to be logic 1 all. EPROM use a floating-gate avalanche-injection MOS (FAMOS) transistor cell to store charge. Applying a special programming voltage (Vpp) cause a high electric field to be developed in the channel region of the transistor. This is in turn causes electrons to jump the silicon dioxide barrier between the channel region and the floating gate. During programming the select gate is given a positive bias which helps attract these electrons to the floating gate electrode. Because the floating gate is surrounded by silicon dioxide, the injected charge is effectively trapped. Cell with trapped charge cause the transistor to be biased on, where as those cells without trapped charge are biased off. Blank EPROMs have no trapped charge and each cell store a logic 1. The electrons on the floating gate absorb photons from the ultraviolet light source and acquire enough energy to reverse the programming process and return to the substrate.

Pursuit of Dignity 


B. ERASER  

 There are many type of EPROM eraser sold in the market, but the price is too high. If we want to do some work, we can build an EPROM eraser with a low cost. Here it is.
To get an ultraviolet lamp, we can used a specific lamp from philips, i.e.: TUV 6 W. this lamp has a wave-length that match for our purpose. This lamp usually used for sterilization medical devices. May be this type quiet hard to find. Another type is Germicidal lamp. This is also for sterilize. I have used this one and seems to work good.
Prom Nights from Hell 
More about Germicidal lamp please visit Sci.Electronics FAQ: Cheap EPROM Eraser
Last search about Germicidal lamp, I got a catalog info at my office from 'EYE' maker, one of the largest lamp maker. Here if you want to see it.

Note that neon lamp type usually used for aquarium accessory can not be used, because the wave-length is not match.
The lamp is about 5 to 10 W. Almost the same as the general neon lamp. The glass is clear, and the fillament can be seen directly. The length about 15 to 25 cm depends on the rating. Used a 10 W / 220 V ballast coil and a starter. Figure I-1. shows the schematic diagram for this lamp connection (the same like conventional neon lamp). Except this kind of circuit, many electronically ballast sell on the market can be used too!
New BOSCH Evaluation/Shuttle Board For Digital Pressure Sensor BMP085 Temperature Measurement 
'Electrolux' product sell this ultraviolet kind of lamp, for their water purifier product part. This can be used also.
Warning!!! Be careful when apply circuit to main line, allways check and recheck the circuit before connecting it in the first time, and also keep in mind that do not see the lamp light directly because ultraviolet light can make you blind !







Fig I-1. Neon lamp wiring schematic.

  • Part list for the eraser circuit :
    1. Neon ballast coil, 10W/220V.......................................................... 1 pce
    2. Neon Starter, 10 - 65W................................................................. 1 pce
    3. Germicidal lamp, type: G8T5, GL-8, 8W........................................... 1 pce
    4. Neon fitting................................................................................. 2 pcs
    5. Electrical switch, 2A/220V.............................................................. 1 pce
    6. Main outlet plug connector, 2A/220V............................................... 1 pce
C. TIMING CIRCUIT  

The erasing time of an EPROM variate about 10 to 40 minutes. It is a pity to waste our time to waiting it while watch the clock round until the EPROM has to be erased. Here a circuit to get the perfect time while it is erased, we can do some another work and let the eraser work by it self. Figure I-2. shows this timer circuit diagram.






Fig.I-2. Timer circuit diagram.

  • Part list for the timer circuit :
    • Resistors :
    1. R1=10 kOhm ............................................................................ 1 pce
    2. R2=180 kOhm .......................................................................... 1 pce
    3. R3, R4, R6=56 kOhm ................................................................. 3 pcs
    4. R5=100 kOhm .......................................................................... 1 pce
    5. R7, R8=1 kOhm ........................................................................ 2 pcs
    6. R9=470 Ohm ............................................................................ 1 pce
    7. Variable P1=50 kOhm ................................................................ 1 pce
    • Capasitors :
    1. C1=470 uF/16V (electrolith) ...................................................... 1 pce
    2. C2=100 nF (ceramic) ................................................................ 1 pce
    3. C3=10 uF/10V (electrolith) ........................................................ 1 pce
    4. C4=330 nF (ceramic) ................................................................ 1 pce
    5. C5=1 uF (non polar) ................................................................. 1 pce
    • Diodes :
    1. D1=1N 4001 ............................................................................ 1 pce
    2. D2=Red LED ............................................................................ 1 pce
    3. D3=Yellow LED ........................................................................ 1 pce
    4. D4=1N 4148 ............................................................................ 1 pce
    5. Bridge BD=1N 4001 .................................................................. 4 pcs
    • Semiconductors :
    1. Transistor T1, T3=BC 557 ......................................................... 2 pcs
    2. Transistor T2=BC 160 ............................................................... 1 pce
    3. IC1=7805 ............................................................................... 1 pce
    4. IC2=4060 ............................................................................... 1 pce
    • Others :
    1. Transformer Tr1=500mA/6V sec, 220V pri ................................... 1 pce
    2. Relay Re1=5V/100mA or 6V/100mA ........................................... 1 pce
    3. Push on switch S1 ................................................................... 1 pce
    4. Microswitch S2 .........................................................................1 pce
    5. Selector switch 1P3T (rotary) S3 ................................................ 1 pce
D. CONSTRUCTION

Because the lamp must not be seen directly when on, so we must make the box fully closed. Figure I-3. shows an example of the construction box. The dimension depends on the lamp size.







Fig. I-3. EPROM eraser box construction.

More attention to mounting the microswitch in the cover box. It must be on when the cover is fully closed or the circuit is never work Also it is not right if the microswitch has to be on when the cover not fully closed yet. Set the distance between the ICs and lamp about 2 to 3 cm length. You can add some hole in the bottom of box for ventilation, because when the lamp is on, the temperature inside may be rised. This was not showed in the figure, but I had added it in my prototype. There is some gap between the styroform and the bottom of box. So, you can make this hole. Use small hinges to open or close the cover. The box divide by two section. The back section is to mounting the timer PCB, ballast coil and lamp starter. Also some panel in the top of box for push button set/reset, power indicator lamp, and the selector switch to choose the right time to exposure the EPROM.
 
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