Toner transfer is a method (common in hobby PCB making)
of printing your circuit board on paper, then using heat and
pressure to de-laminate the plastic toner onto the clean, bare
copper untreated (and cheap) PCB.
It can be done with ink jet photo paper and a clothes
iron, but you get more consistent results if you use a laminator
and glossy paper. I use Hammermill Laser Gloss, but others
have had good results with the gloss paper used in magazine
You print the resist pattern on the paper, use the iron or
laminator to transfer it to the copper, then you soak the paper
in water to make it easy to remove. The plastic toner stays on
the copper, and makes an excellent etch resist.
It takes a little practice to get the technique down, but
once you have it you can knock out good prototype boards for
essentially the cost of the copper board.
see if I could build a better charger (with two smart charger
circuits) that would fit in exactly the same slot as the
current printed circuit board (PCB); see Figure 1.
Cramming all these components in this tiny space
meant I would have to use surface-mount components.
That’s right up my alley anyway, as I use them exclusively
for all the circuit boards I make. This has the drawback that
I can’t prototype things as easily as with through-hole
components and a breadboard, but there is the advantage
that when I have a working product, I don’t have to
convert it to the final form. I just have to stick it in a case
and move on. I do my prototyping using software design
and simulation tools, specifically NI Multisim (a descendant
of Electronic Workbench), and minimize my breadboard
costs by buying in bulk and making my own PCBs. SMD
components are much less expensive than through-hole
There are basically two methods of smart-charging
NiCd and NiMH batteries: one method detects the fall in
voltage that happens when the battery is fully
charged and is called delta V; the other method
detects the rise in temperature of the fully charged
battery and is called delta T. I decided to forgo the
temperature change method of determining that the
batteries are charged, and instead used the delta V
method. This way, I didn’t have to fiddle with trying
to sense the temperature of the batteries in the stock
Versapak battery holder. Sensing the temperature of
the batteries would require putting thermistors in
physical contact with the batteries, and I didn’t want
to have to make the modifications to the holder that
this would entail.
There are quite a few manufacturers of smart
charger chips, but Mouser (my favorite electronics
supplier) carries the MC33340DG made by ON
Semiconductor which happens to use the delta V
method for primary charge termination. It also
supports elapsed time or even thermistor temperature
sensing as secondary methods for
terminating charging. And at $1.45, each
they are fairly inexpensive.
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