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| 5/26 |
| 2008/6/22-27 [Science/Electric] UID:50331 Activity:nil |
6/22 I got a bunch of AA batteries that are about 0.8 - 0.9V. They're
not strong enough to power the devices I need. What are some creative
ways to get the most out of your batteries besides recycling?
\_ Look up "Joule thief"
\_ Seconded
\_ Wow, that's cool. I have all the parts except the transistor.
Anyone know where I can find a transistor really cheap/free?
\_ Here's an improved circuit that includes a capacitor:
http://www.talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html
http://preview.tinyurl.com/2llkrq [talkingelectronics]
\- http://www.slate.com/id/2193827 |
| 5/26 |
|
| www.talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html From a single AAA cell to 4, 5 and 6 "D" cells, as well as "lantern" and "fisherman's." This project uses a white LED to produce illumination equal to a small torch. A 1,000mcd white LED used in this project had a characteristic voltage of 35v and a 3,000mcd white LED had a characteristic voltage of 32v. Both LEDs were driven at 20mA and the 3candala LED produced a brighter, whiter light while the 1candella LED had a yellowish ring around the edge of the illumination. A LED torch is one of the simplest projects you can build and it's very interesting as it uses a super-bright white LED. In the history of LED production, red LEDs were the first to be invented and their output was so dim you could barely see if they were illuminated. As time went by, the brightness improved and it came to a point where the output would shine into the surrounding air. At first it was dull, but gradually the output increased to a dazzling glare. With the combination of red, green and blue, manufacturers had the potential of producing a white LED. Since the illumination produced by a LED comes from a crystal, it is not possible to produce white light from a single crystal or "chip." As soon as the output of blue came up to the quality of the other colors, a white LED was a marketable product. White LEDs are now with us and their output makes them a viable alternative to the globe. Although a LED torch is passable for illuminating an area, it certainly does not have the illuminating capability of a $10 lantern, using a 6v battery. A LED torch is more of a "fun-thing" to see how far LEDs have come in the past few years and see what can be done with a single cell and an handful of components. When we first decided to produce a LED torch project, we wanted to fit the circuit into a 2-cell torch but a white LED requires about 34v to operate, and two cells produce only 3v. So we had to think of a number of ways around the problem. As you know, a LED will not operate on a voltage below its characteristic voltage. This characteristic voltage depends on the type of LED and is about 17v for a normal red LED, while a super-bright LED is about 31v - 4v. The exact characteristic voltage varies with the colour, the intensity of the LED, the current flowing and the way it is manufactured. This feature cannot be altered after it is manufactured and the EXACT voltage must be delivered, otherwise the LED will be not work or if the voltage is higher, it will be destroyed. The supply voltage must exactly match the characteristic voltage. This sounds a difficult thing to do, but a simple solution is to add a resistor in series and the voltage across the LED will sit at the exact value required by the LED, while the extra voltage will appear across the resistor. According to Ohm's Law, a current will flow though the resistor and this will also flow though the LED. This applies when the circuit is supplied with a DC voltage. All we have to do is create a voltage higher than 34v and we can drive one of the latest SUPER-HIGH-BRIGHT white LEDs with a single cell, using a step-up-voltage circuit. This will produce a series of pulses to the LED and the brightness will be slightly higher than if a steady DC voltage is applied. These are the things we will be covering in this project. This project explains the operation of a "transformer" in flyback mode. A transformer is one of the most complex items in electronics. Even a simple hand-made "transformer" requires a lot of understanding to see how it works. CIRCUIT A The first circuit in this discussion is the simplest design. It consists of a transistor, resistor and transformer, with almost any type of LED. The circuit will drive a red LED, HIGH BRIGHT LED, or white LED. The circuit produces high voltage pulses of about 40v p-p at a frequency of 200kHz. Normally you cannot supply a LED with a voltage higher than its characteristic voltage, but if the pulses are very short, the LED will absorb the energy and convert it to light. The characteristic voltage of the LED we used was very nearly 4v and this means the voltage across it for a very short period of time was 4v. The core was a 26mm diameter "slug" 6mm long and the wire was 095mm diam. In fact any core could be used and the diameter of the wire is not important. The number of turns are not important however if the secondary winding does not have enough turns, the circuit will not start-up. HOW THE CIRCUIT WORKS The transformer is configured as a BLOCKING OSCILLATOR and the cycle starts by the transistor turning on via the 2k7 base resistor. This causes current to flow in the 60-turn main winding. The other winding is called the feedback winding and is connected so that it produces a voltage to turn the transistor on MORE during this part of the cycle. This winding should really be called a "feed-forward" winding as the signal it supplies to the transistor is a positive signal to increase the operation of the circuit. This voltage allows a higher current to flow in the transistor and it keeps turning on until it is saturated. At this point the magnetic flux produced by the main winding is a maximum but it is not expanding flux and thus it ceases to produce a voltage in the feedback winding. This causes less current to flow into the base of the transistor and the transistor turns off slightly. The flux produced by the main winding is now called collapsing flux and it produces a voltage in the feedback winding of opposite polarity. This causes the transistor to turn off and this action occurs until it is completely off. The magnetic flux continues to collapse and cuts the turns of the main winding to produce a very high voltage of opposite polarity. However this voltage is prevented from rising to a high value by the presence of the LED and thus the energy produced by the collapsing magnetic flux is converted to light by the LED. The circuit operates at approx 200kHz, depending on the value of the base resistor and physical dimensions of the transformer. The circuit draws 85mA from the 15v cell and the brightness of the LED was equivalent to it being powered from a DC supply delivering 10 - 15mA. Before we go any further, there are a number of interesting circuits on the web. The first circuit is identical to our "Circuit A" except the design engineer did not do his homework. He only added 8 turns to the 100uH inductor and found the circuit did not start-up. His solution was to add another transistor and tie the base to the collector. The second transistor is being turned on via a 1k resistor on the collector of the first transistor and when this "turn-on" current is not required, it is being shunted to "deck." Our circuit uses the "oomph" of the secondary winding to saturate the transistor and this produces the highest efficiency. Apart from the circuit being enormously complex and expensive, 62mA is too high for many white LEDs. Maybe the signal at the transformer end of the 220R needs to be stabilised to improve the performance of the circuit. But I actually thought of placing a small capacitor at the join and taking the other end to the 0v rail. This will allow rail voltage to enter the feedback winding of the transformer but prevent the signal generated by the winding being lost through the 2k7 resistor. The brightness of the LED did not alter but the current changed from 85mA to 28mA. The frequency of the circuit changed from 200kHz to 500kHz. The LED was getting more than twice the number of pulses per second. This improvement has never been presented in any circuit on the web. If the brightness of the LED is equal to a DC voltage of 4v and a current of 10mA, the circuit we have produced is slightly more efficient than delivering a DC voltage to the LED, even though there are some losses in the transformer and transistor. This proves the fact that LEDs driven with a pulse, are more efficient than being driven by a DC supply. With this we turn to a surface-mount chip that has been designed to carry out the exact same task as circuit B The chip is called PR4401. I could not find any sales literature on the internet, but the manufacturer requires 9,000 pieces to be bought at a c... |
| preview.tinyurl.com/2llkrq -> www.talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html From a single AAA cell to 4, 5 and 6 "D" cells, as well as "lantern" and "fisherman's." This project uses a white LED to produce illumination equal to a small torch. A 1,000mcd white LED used in this project had a characteristic voltage of 35v and a 3,000mcd white LED had a characteristic voltage of 32v. Both LEDs were driven at 20mA and the 3candala LED produced a brighter, whiter light while the 1candella LED had a yellowish ring around the edge of the illumination. A LED torch is one of the simplest projects you can build and it's very interesting as it uses a super-bright white LED. In the history of LED production, red LEDs were the first to be invented and their output was so dim you could barely see if they were illuminated. As time went by, the brightness improved and it came to a point where the output would shine into the surrounding air. At first it was dull, but gradually the output increased to a dazzling glare. With the combination of red, green and blue, manufacturers had the potential of producing a white LED. Since the illumination produced by a LED comes from a crystal, it is not possible to produce white light from a single crystal or "chip." As soon as the output of blue came up to the quality of the other colors, a white LED was a marketable product. White LEDs are now with us and their output makes them a viable alternative to the globe. Although a LED torch is passable for illuminating an area, it certainly does not have the illuminating capability of a $10 lantern, using a 6v battery. A LED torch is more of a "fun-thing" to see how far LEDs have come in the past few years and see what can be done with a single cell and an handful of components. When we first decided to produce a LED torch project, we wanted to fit the circuit into a 2-cell torch but a white LED requires about 34v to operate, and two cells produce only 3v. So we had to think of a number of ways around the problem. As you know, a LED will not operate on a voltage below its characteristic voltage. This characteristic voltage depends on the type of LED and is about 17v for a normal red LED, while a super-bright LED is about 31v - 4v. The exact characteristic voltage varies with the colour, the intensity of the LED, the current flowing and the way it is manufactured. This feature cannot be altered after it is manufactured and the EXACT voltage must be delivered, otherwise the LED will be not work or if the voltage is higher, it will be destroyed. The supply voltage must exactly match the characteristic voltage. This sounds a difficult thing to do, but a simple solution is to add a resistor in series and the voltage across the LED will sit at the exact value required by the LED, while the extra voltage will appear across the resistor. According to Ohm's Law, a current will flow though the resistor and this will also flow though the LED. This applies when the circuit is supplied with a DC voltage. All we have to do is create a voltage higher than 34v and we can drive one of the latest SUPER-HIGH-BRIGHT white LEDs with a single cell, using a step-up-voltage circuit. This will produce a series of pulses to the LED and the brightness will be slightly higher than if a steady DC voltage is applied. These are the things we will be covering in this project. This project explains the operation of a "transformer" in flyback mode. A transformer is one of the most complex items in electronics. Even a simple hand-made "transformer" requires a lot of understanding to see how it works. CIRCUIT A The first circuit in this discussion is the simplest design. It consists of a transistor, resistor and transformer, with almost any type of LED. The circuit will drive a red LED, HIGH BRIGHT LED, or white LED. The circuit produces high voltage pulses of about 40v p-p at a frequency of 200kHz. Normally you cannot supply a LED with a voltage higher than its characteristic voltage, but if the pulses are very short, the LED will absorb the energy and convert it to light. The characteristic voltage of the LED we used was very nearly 4v and this means the voltage across it for a very short period of time was 4v. The core was a 26mm diameter "slug" 6mm long and the wire was 095mm diam. In fact any core could be used and the diameter of the wire is not important. The number of turns are not important however if the secondary winding does not have enough turns, the circuit will not start-up. HOW THE CIRCUIT WORKS The transformer is configured as a BLOCKING OSCILLATOR and the cycle starts by the transistor turning on via the 2k7 base resistor. This causes current to flow in the 60-turn main winding. The other winding is called the feedback winding and is connected so that it produces a voltage to turn the transistor on MORE during this part of the cycle. This winding should really be called a "feed-forward" winding as the signal it supplies to the transistor is a positive signal to increase the operation of the circuit. This voltage allows a higher current to flow in the transistor and it keeps turning on until it is saturated. At this point the magnetic flux produced by the main winding is a maximum but it is not expanding flux and thus it ceases to produce a voltage in the feedback winding. This causes less current to flow into the base of the transistor and the transistor turns off slightly. The flux produced by the main winding is now called collapsing flux and it produces a voltage in the feedback winding of opposite polarity. This causes the transistor to turn off and this action occurs until it is completely off. The magnetic flux continues to collapse and cuts the turns of the main winding to produce a very high voltage of opposite polarity. However this voltage is prevented from rising to a high value by the presence of the LED and thus the energy produced by the collapsing magnetic flux is converted to light by the LED. The circuit operates at approx 200kHz, depending on the value of the base resistor and physical dimensions of the transformer. The circuit draws 85mA from the 15v cell and the brightness of the LED was equivalent to it being powered from a DC supply delivering 10 - 15mA. Before we go any further, there are a number of interesting circuits on the web. The first circuit is identical to our "Circuit A" except the design engineer did not do his homework. He only added 8 turns to the 100uH inductor and found the circuit did not start-up. His solution was to add another transistor and tie the base to the collector. The second transistor is being turned on via a 1k resistor on the collector of the first transistor and when this "turn-on" current is not required, it is being shunted to "deck." Our circuit uses the "oomph" of the secondary winding to saturate the transistor and this produces the highest efficiency. Apart from the circuit being enormously complex and expensive, 62mA is too high for many white LEDs. Maybe the signal at the transformer end of the 220R needs to be stabilised to improve the performance of the circuit. But I actually thought of placing a small capacitor at the join and taking the other end to the 0v rail. This will allow rail voltage to enter the feedback winding of the transformer but prevent the signal generated by the winding being lost through the 2k7 resistor. The brightness of the LED did not alter but the current changed from 85mA to 28mA. The frequency of the circuit changed from 200kHz to 500kHz. The LED was getting more than twice the number of pulses per second. This improvement has never been presented in any circuit on the web. If the brightness of the LED is equal to a DC voltage of 4v and a current of 10mA, the circuit we have produced is slightly more efficient than delivering a DC voltage to the LED, even though there are some losses in the transformer and transistor. This proves the fact that LEDs driven with a pulse, are more efficient than being driven by a DC supply. With this we turn to a surface-mount chip that has been designed to carry out the exact same task as circuit B The chip is called PR4401. I could not find any sales literature on the internet, but the manufacturer requires 9,000 pieces to be bought at a c... |
| www.slate.com/id/2193827 As a woman who loves sports, I've always found the concept of breasts bothersome. If all goes according to plan, they will fulfill their intended function for about three of the 70 years that I have them. The rest of the time, they alternate between getting in my way and embarrassing me. They are a favorite target of Frisbees and soccer balls. I am still tortured by the memory of three cousins standing in a circle around me, at the impressionable age of 10, mocking my early development and telling me that I was going to be the Asian Dolly Parton. Fortunately, that never happened, but the possibility haunted my late childhood. As I rode public transportation to the office, my messenger bag slung uncomfortably across my chest, I thought, "Why not put the girls to work?" solar-powered bra that supposedly will generate enough energy to power an iPod. But I live in foggy San Francisco and prefer not to walk around in my underwear in public. It turns out that the physics of breast motion have been studied closely for the last two decades by a gamut of researchers, most of them women. LaJean Lawson, a former professor of exercise science at Oregon State University, has studied breast motion since 1985 and now works as a consultant for companies like Nike to develop better sports bra designs. Lawson was enthusiastic about my idea but warned it would be tricky to pull off. You would need the right breast size and the right material, she explained, and the bra itself would have to be cleverly designed. "It's just a matter of finding the sweet spot, between reducing motion to the point where it's comfortable but still allowing enough motion to power your iPod," she said. Lawson explained that breasts move on three different axes: from side to side, front to back, and up and down. Naturally, the bigger the breast, the more momentum it generates. "Let's face it--if you're a double-A marathoner, you're probably not going to get that iPod up and running," Lawson said. Fabric and design are also important factors in distance traveled. Choosing between an encapsulation design, in which the cups are separated, or a compression design, where they are hugged close to the body, can also affect breast motion. An encapsulation design further reduces motion because two smaller masses are easier to control than one large one. "Also, if you have a really high neckline, the breasts won't fly up," Lawson said. So I was in the market for an elastic, compression-style bra with a low neckline. Of course, even a bra that perfectly maximized motion (without sacrificing support and comfort) would be useful to me only if there were a way to turn that motion into energy. For a primer on how to do that, I turned to Professor Zhong Lin Wang of Georgia Tech, who is currently working to develop fabric made from nanowires that will capture energy from motion. Wang's wires are about 1/1,000^th the width of a human hair. When woven together in a fabric, these nanowires rub up against one another and convert the mechanical energy from the friction into an electric charge. According to Wang, the fabric is cheap to produce and surprisingly efficient; his team hopes to use it to create energy-generating T-shirts and other articles of clothing. A square meter of fiber produces about 80 milliwatts of power, which is enough to run a small device like a cell phone. Wang expects to have a shirt available for purchase within five years. Many bra patterns call for about a meter of fabric, which would probably mean that a regular bra would have enough energy to power an iPod. But the fabric could also be layered, doubling or even tripling the amount of energy produced. I asked Wang whether his fabric could be used to make a bra. "There is a lot of friction and movement in that general area. Share with Stumble Upon Adrienne So is a researcher and writer for Wired magazine. Join the Fray: our reader discussion forum What did you think of this article? |