Paul emailed and said he has built his 12th Joule Thief. Man, this guy is Helen Wheels – an even dozen in a matter of a fortnight (or week or two, I forget which).
I’ve been puttering with the TE Flashers. I made most of them on small pieces of “Woodsie” wood that I got from Michaels arts and crafts store. I was getting low on the 3/4″ by 1-1/2″ size, so I stopped by their store to get some more. But they were out of those, so I looked at a 4 by 12 inch piece of 1/8″ thick birch plywood, the kind used for building model airplanes. I decided to buy one for a buck and a half, less than a soft drink at a fast food joint. I sawed off a couple strips to make more squares. Then I peeled off the label, which took almost the whole end, one third of the total board. I managed to get the label off in one piece, but the board was covered with the sticky, gooey glue they used on the label. I can’t believe they could cause such a big mess on something they know is going to be used on a model, where looks are so important. It has already picked up dirt and dust, and I can’t paint over it with the clear sealer, so I’m going to go back and get my money back and see if they have any of the Woodsie wood pieces in stock.
The pieces I had already cut are going to get the parts for the TE flasher mounted on them. I think they will be my fourth and fifth? Whatever. I’ll use yellow LED for the most visual impact. The yellow LEDs measured 2.4V at 28 or so mA, so this circuit drives them with no problems.
I bought some LEDs of various colors including red from alanparekh.com a few years ago, and at that time I found that the blue ones all had bubbles in them. I complained and he replaced them. But because I had a bag of 100 of very bright red LEDs from superbrightleds.com, I didn’t open the red LEDs from alanparekh.com until recently. Now I find that the red ones put out a small fraction of the light that the superbright LEDs put out, and it’s too late to complain. I think I’ve learned my lesson: to never buy any more LEDs from eBay sellers and the like, and stick with the big distributors even if it costs more. I’ll get a lot better product in the end.
Update Mar 10 – Paul said that after he has run the cells down to less than a volt, he runs the JT using two almost dead cells in series. I’ve been running more than a half dozen germanium JTs with cells less than a volt, and they run the cells down to less than 0.3V before the LED dims to darkness. I have found that many of the cells leak, and I’m glad I put a piece of pressed board on the shelf, to save the shelf from damage. It now has leakage spots all over. Since I’m using small magnets to hold the wires to the batteries, there is no holder to be damaged by the leaking. My thought is that if the cells had not been so run down they may not have leaked so often. In the end the cells I’ve put on the germanium JTs are less than a hundred millivolts, and ready for the trash can.