SC_Eraser.pdf

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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
1000~
capacitor is connected in parallel with the on-
board
220~F
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
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 devel­
oping microprocessor-based projects
needed access to an ultra-violet (UV)
eraser. Unlike current technology de­
vices that can be electrically erased in
seconds without even removing them
from circuit, older EPROM-based de­
vices 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 EPROM­
based 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 home­
built 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 tooth­
brushes 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 add­
ing a 1OOO!1F capacitor in parallel with the existing 220!1F
capacitor in the timing circuit. This larger total capaci­
tance 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/cm
2 ),
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 220!1F timing capacitor (the largest
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
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For more information about
the TPS2000 family...
Talk to NewTek Instruments:
Ph:
02 9888 0100
email: info@newtekinstruments.com
NewTek Instruments Pty Ltd • Sydney - Melbourne
Tektronix·
Enabling Innovation
/
siliconchip. com. au
...
NewTek Instruments
1-.-----------
------------·1
115
2.5mm THICK
PLASTIC SHEET
WOODEN DOWELS
45mm LONG x 9mm DIA.
(All DIMENSIONS IN MILlIMETRES)
I·
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.
51 __
'~11J
do both jobs with a couple of simple
additions. First, a switch can be insert­
ed in series with the lOOOJ..lF 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 l2mm countersunk screws. A
piece of conductive foam is then glued
to the face.
one). Solder a lOOOJ..lF 25V electrolytic
capacitor in parallel with this capaci­
tor. 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 po­
sition 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!
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 oc­
curs 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 lA plugpack produced 9.2V when
supplying the modest (llOmA) current /
demands of the holder. A lN4004 di-'
ode is series with the supply brought
SC
this back to the desired 8.5V
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 substi­
tute 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
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
dosed for the unit to operate.
82
SILICON CHIP
V
siliconchip. com. au
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