Cheap EPROM Eraser - Silicon Chip March 2005

[Steve Carroll]

I'm building an EPROM eraser from a toothbrush steriliser as described in "A
Cheap UV EPROM Eraser", Silicon Chip, March 2005. I don't have the article
in front of me and need to know the value of the cap that must be added. (I
assume that the cap must be added to alter the timer's period.)
Any other comments on the article/project are welcome.

Any help would be appreciated,
Steve.

 

[Franc Zabkar]

I'm building an EPROM eraser from a toothbrush steriliser as described in "A
Cheap UV EPROM Eraser", Silicon Chip, March 2005. I don't have the article
in front of me and need to know the value of the cap that must be added. (I
assume that the cap must be added to alter the timer's period.)
Any other comments on the article/project are welcome.

Any help would be appreciated,
Steve.

Add a 1000uF cap in parallel with the existing 220uF cap.

BTW, check that your LED isn't wired with reverse polarity. Mine was.
:-(

- Franc Zabkar

 

[Steve Carroll]

Add a 1000uF cap in parallel with the existing 220uF cap.

BTW, check that your LED isn't wired with reverse polarity. Mine was.
:-(

- Franc Zabkar

Excellent - thanks Frank. (I'll check the LED)
.... Steve

 

[Steve Carroll]

Add a 1000uF cap in parallel with the existing 220uF cap.

BTW, check that your LED isn't wired with reverse polarity. Mine was.
:-(

- Franc Zabkar

The LED was wired correctly, but they forgot to poke it into the hole in the
front case, so it wasn't visible. Even better, one of the wires on the UV
tube wasn't soldered on, it was attached with a hot glue gun. Despite this,
it actually worked, but only lit up 4 out of 5 times. All fixed now, and a
good little eraser. Takes 15 minutes. (Better than 36 hours with a UV insect
tube.)
.... Steve

 

[Steve]

Add a 1000uF cap in parallel with the existing 220uF cap.

BTW, check that your LED isn't wired with reverse polarity. Mine was.
:-(

- Franc Zabkar

As a final note on this one, the LED on mine was in backwards too. I didn't
realise it early on since it was still lighting. Having traced the circuit,
I think thet the LED/resistor combo doubles as a snubber, to prevent
excessive flyback voltage on the collector of the transistor. A novel
method, but it works fine. I've since pulled out all of the original timing
components and replaced them with a PIC16C711, a pot and an LCD display to
set the time easily between 0 and 60 minutes. It works really well, and
erases most chips in 20 minutes. A shame that Jaycar no longer sell the
toothbrush sterilisers.

.... Steve

 

[Franc Zabkar]

As a final note on this one, the LED on mine was in backwards too. I didn't
realise it early on since it was still lighting. Having traced the circuit,
I think thet the LED/resistor combo doubles as a snubber, to prevent
excessive flyback voltage on the collector of the transistor. A novel
method, but it works fine.

Thanks for the correction.

I've since pulled out all of the original timing
components and replaced them with a PIC16C711, a pot and an LCD display to
set the time easily between 0 and 60 minutes. It works really well, and
erases most chips in 20 minutes.

I was also thinking of replacing the timing stuff with something
adjustable.

A shame that Jaycar no longer sell the
toothbrush sterilisers.

... Steve

Yeah, I searched the Internet for an alternative but couldn't find
anything similar.

- Franc Zabkar