Here's a link to the circuit we're talking about.
http://www.netcentral.co.uk/satcure/design/microtor.htm
I've talked to Martin and here was his reply:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> These ferrite beads cost only pennies
What I'll do is to post 100 to Ken on (hopefully) Tuesday. You can all
then fight amongst yourselves
The wire is 38SWG or 0.0060". I don't know what this is in AWG but I'm
sure you can find out. The stuff I use is polyurethane coated. You need a
90cm length. That's a yard. You fold it in half and thread the folded end
through the bead until only two 1.5 inch tails remain. Then thread the
folded end through the bead another 19 to 20 times. Finally, snip the
folded end so you have four wires. Measure them for continuity so you can
pair them and solder two non-connected ends together. Take care when you
"tin" the ends because the urethane gives off poisonous fumes.
The resistor is 10k. You can reduce this to 2K which will increase the
*average* LED current from 18mA to 30mA - more than enough for a
hyperbright LED! Obviously, if you decide to use a PNP transistor, you
have to reverse the LED and battery connections. The physical size of
this circuit is tiny. I used a surface mount resitor, cut the transistor
leads real short and mounted the whole thing inside my old General Motors
car key *instead* of the existing bulb!! The most efficient transistor is
the ZTX650. Other transistors work but at reduced efficiency. A ZTX650
gives 79 percent efficiency, a ZTX450 73 percent and a BC550 57 percent.
I have used four white LEDs in series. These ran at full brightness for
12 hours off a 1.5v mercury "button" cell. For the next 12 hours the
brightness gradually reduced. Of course, you could run it off one or two
"D" cells (large torch cells) and it would run for weeks.
If you can club together to send me $20 for the beads then I'll be happy.
I can also supply the wire and transistors, if required. You have till
Monday night to decide.
I get the white LEDs from **** Smith Electronics in Australia. You could
club together to make up an order and pay by credit card to save time. (I
can't accept credit cards yet).
Well, I won't make much profit from this but I'm just pleased to see
people actually interested in Electronics. There aren't many of us left.
Most people nowadays think it's essential to use a microcontroller or a
PIC to make even a simple oscillator!
Kind Regards,
Martin
Martin T. Pickering B.Eng.
<HR></BLOCKQUOTE>
I will send Martin $20 and KenBar whatever it costs for him to ship 100 beads to me here in Indiana.
Then I will offer the beads "at cost" plus shipping to anyone interested.
Hope this helps to inspire some neat new LED lights!