Saturday, July 11, 2009
Thank heaven for 7-11 - Heh-heh
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Someday I'm going to get around to cataloging all of the electronics nahuals and books that I've collected over the years. They're a wealth of information on circuits, components and electronic theory, some of them obviously old and outdated. But then sometimes it's goof to have a data sheet on an old part so I can find out a more modern equivalent.
Some circuits have been around for fifty years or more, with just a few changes to update them to newer components. I have GE and RCA Transistor Manuals from the 1960s that have the complimentary coupled OTL audio amplifier circuits that are still used today. Silicon transistors were hard to find in the early '60s so they mostly used Germanium, but the circuits are still the same.
Then there's the theory and math. That hasn't changed in a very long time. A volt is still a volt as it has been for a century. Learn your theory and it's good for your life. Admittedly you may be working in Gigahertz instead of Megahertz, but a Hertz is still a Hertz and has been since they changed from cycles per second in the early '60s.
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Someday I'm going to get around to cataloging all of the electronics nahuals and books that I've collected over the years. They're a wealth of information on circuits, components and electronic theory, some of them obviously old and outdated. But then sometimes it's goof to have a data sheet on an old part so I can find out a more modern equivalent.
Some circuits have been around for fifty years or more, with just a few changes to update them to newer components. I have GE and RCA Transistor Manuals from the 1960s that have the complimentary coupled OTL audio amplifier circuits that are still used today. Silicon transistors were hard to find in the early '60s so they mostly used Germanium, but the circuits are still the same.
Then there's the theory and math. That hasn't changed in a very long time. A volt is still a volt as it has been for a century. Learn your theory and it's good for your life. Admittedly you may be working in Gigahertz instead of Megahertz, but a Hertz is still a Hertz and has been since they changed from cycles per second in the early '60s.
Tuesday, July 07, 2009
I'm sick and tired of all the media attention to M.J. and his untimely death. I have nothing against the popular star, but I think the media is doing a tremendous disservice to the majority of the population who feel indifferent like me, in order to cater to a small minority of fans who don't make up enough of the population to justify the media attention. I hope this all blows over so we can get back to the real news that is not waiting to happen just because some single relatively unimportant person dies. There are much more important things happening all around the world. Sometime in the last few days it came down to a point where a person is pushed into a corner where he has to just scream out "ENOUGH! I've had it, and I ain't gonna take it any more." And he reaches for the remote and CLICK! it's off, done, finished, ended.
I found a different version of a Phase Shift Oscillator that drives an LED so the light varies continuously instead of being just swtched on and off. It can be found here. The text is in German, by the way.
Back to experimenting...
I found a different version of a Phase Shift Oscillator that drives an LED so the light varies continuously instead of being just swtched on and off. It can be found here. The text is in German, by the way.
Back to experimenting...
Wednesday, July 01, 2009
1st of month update, Youtube opinion re Joule Thiefs
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It's the first of the month, and my blue blinky is still blinking. It's been running on the same single AA cell since Dec 1, 2007.
I did a lot of viewing of JT and similar circuits on Youtube, and many were informative. but I have two opinions, and I mean these to be constructive criticism, so that the people who post these videos can help us, the viewers, in understanding what is being displayed.
First off, there must be some companies in Asia that are becoming billionaires from selling alligator clip leads to YouTube experimenters. What I see repeatedly is a rat's nest of alligator clip leads laying around on a desk, connecting up the various components and equipment. Folks, this is not professional, and it makes it difficult to show anyone what is actually connected up.
I'm not asking anyone to learn to solder. That's not necessary; all you need is a small screwdriver. There are terminal strips that can be cut up and used to hold and connect components and wires together. These are available from the same place you got the clip leads, Radio Shack is one place. You can get the model 274-680 Euro Mini Strip and cut it into pieces of two terminals with a hacksaw, and use it to hold a single component, or leave it larger to hold more parts and/or wires.
You're probably complaining that you can't make or break connections with this easily like you can with alligator clips. Well, buy a switch and put it in the circuit. Or if you insist, connect an alligator clip up to the terminal strip. But by all means, get rid of that rat's nest of wires laying on the desk. Make it neater so you can show us what's connected to what.
The reason you YouTube posters need to show us what's connected to what is because almost every schematic or wiring diagram I've seen on YouTube or on a link from YouTube is difficult at best to understand and sometimes unreadable. The usual problem on YouTube is the poster attempts to show it with the camcorder, but it comes out too blurry to read. But a major reason for misunderstanding is the poster uses symbols that are misunderstood or not understood by the viewers.
One help is to download a free software program called ExpressPCB which has a second program ExpressSCH. This easy-to-use program lets you draw schematic diagrams and even add your own custom components. It will do wonders for making your projects clearer to both you and your viewers. Or if you really need SPICE, download Linear Tech's free SwitcherCAD III.
The poster should go to Instructables.com and post a How-To on building the project, with explanations in pictures, diagrams and text on the project. Then the poster should go to Youtube and post only the finished project in operation. YouTube should not be used for the schematic, pictures and explanations that are so much clearer and better on Instructables. YouTube is great for some things, but it's not a substitute for pictures, diagrams and the printed word.
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It's the first of the month, and my blue blinky is still blinking. It's been running on the same single AA cell since Dec 1, 2007.
I did a lot of viewing of JT and similar circuits on Youtube, and many were informative. but I have two opinions, and I mean these to be constructive criticism, so that the people who post these videos can help us, the viewers, in understanding what is being displayed.
First off, there must be some companies in Asia that are becoming billionaires from selling alligator clip leads to YouTube experimenters. What I see repeatedly is a rat's nest of alligator clip leads laying around on a desk, connecting up the various components and equipment. Folks, this is not professional, and it makes it difficult to show anyone what is actually connected up.
I'm not asking anyone to learn to solder. That's not necessary; all you need is a small screwdriver. There are terminal strips that can be cut up and used to hold and connect components and wires together. These are available from the same place you got the clip leads, Radio Shack is one place. You can get the model 274-680 Euro Mini Strip and cut it into pieces of two terminals with a hacksaw, and use it to hold a single component, or leave it larger to hold more parts and/or wires.
You're probably complaining that you can't make or break connections with this easily like you can with alligator clips. Well, buy a switch and put it in the circuit. Or if you insist, connect an alligator clip up to the terminal strip. But by all means, get rid of that rat's nest of wires laying on the desk. Make it neater so you can show us what's connected to what.
The reason you YouTube posters need to show us what's connected to what is because almost every schematic or wiring diagram I've seen on YouTube or on a link from YouTube is difficult at best to understand and sometimes unreadable. The usual problem on YouTube is the poster attempts to show it with the camcorder, but it comes out too blurry to read. But a major reason for misunderstanding is the poster uses symbols that are misunderstood or not understood by the viewers.
One help is to download a free software program called ExpressPCB which has a second program ExpressSCH. This easy-to-use program lets you draw schematic diagrams and even add your own custom components. It will do wonders for making your projects clearer to both you and your viewers. Or if you really need SPICE, download Linear Tech's free SwitcherCAD III.
The poster should go to Instructables.com and post a How-To on building the project, with explanations in pictures, diagrams and text on the project. Then the poster should go to Youtube and post only the finished project in operation. YouTube should not be used for the schematic, pictures and explanations that are so much clearer and better on Instructables. YouTube is great for some things, but it's not a substitute for pictures, diagrams and the printed word.
Sunday, June 28, 2009
bowdenshobbycircuits.info now Bill Bowden's Hobby Circuits, http://ourworld.compuserve.com/homepages/Bill_Bowden is now history.
IMPORTANT! Bill Biowden informed me last month that Compuserve AKA Compuswerve is shutting down its classic service, including his website at the end of June. Compuswerve is one of the oldest if not the oldest of the original internet providers and predates the internet as a VAN (value added network) similar to AOL and Prodigy.
Bill's website has been the source of some of the most well thought out and comprehensive schematics, with excellent technical quality. As far as I know, he has built and tested them and knows that they do what they are supposed to do, without problems. His circuits have been plagiarized across the net, due to a few losers, mostly in foreign countries, that steal the work of others without giving credit to the original author.
Bill's new website is easy to remember, unlike the old one, which was a mouthful. It's www.bowdenshobbycircuits.info.
I checked it out and it's up and running. Oops, Bill misspelled Discrete Multistage Light Sequencer. If someone searches for Discrete --, they won't hit it, since he has descrete. It wouldn't be important if it wasn't the heading, but it is.
I'm hoping that Google and other search engines pick up the new website quickly. I know I often use it for referencing when I'm building something.
Best of success in the future, Bill.
Update Jun 30 - In reply to his comment about the DMLS. At first I couldn't get it to work. I had to put resistors from bases to emitters to get it to work - can't remember the value. The problem is all the transistors are not conducting when powered on, so something has to be done to get it to start. A sharp transient is needed to get it going. I haven't had time to work further with it since last month.
The obvious solution is this one. It's so glaringly simple that it's impossible to ignore. The 2N7000 is so cheap - $16 a hundred - and the circuit is so simple that it's poor judgment not to use them. And you can replace them with some TO-220 power MOSFETs for well under a dollar each and light up LEDs at an amp or more, or if you're desperate, some automobile taillight bulbs.
That's why I'll probably forget about pursuing the BJT solution further and pull the parts oqff the protoboard when I need it.
An informative Forbes article concerning the shortage of employees in jobs like engineering and tech. Believe it or not, there are jobs out there in these jobless times that are going unfilled due to a lack of applicants.
IMPORTANT! Bill Biowden informed me last month that Compuserve AKA Compuswerve is shutting down its classic service, including his website at the end of June. Compuswerve is one of the oldest if not the oldest of the original internet providers and predates the internet as a VAN (value added network) similar to AOL and Prodigy.
Bill's website has been the source of some of the most well thought out and comprehensive schematics, with excellent technical quality. As far as I know, he has built and tested them and knows that they do what they are supposed to do, without problems. His circuits have been plagiarized across the net, due to a few losers, mostly in foreign countries, that steal the work of others without giving credit to the original author.
Bill's new website is easy to remember, unlike the old one, which was a mouthful. It's www.bowdenshobbycircuits.info.
I checked it out and it's up and running. Oops, Bill misspelled Discrete Multistage Light Sequencer. If someone searches for Discrete --, they won't hit it, since he has descrete. It wouldn't be important if it wasn't the heading, but it is.
I'm hoping that Google and other search engines pick up the new website quickly. I know I often use it for referencing when I'm building something.
Best of success in the future, Bill.
Update Jun 30 - In reply to his comment about the DMLS. At first I couldn't get it to work. I had to put resistors from bases to emitters to get it to work - can't remember the value. The problem is all the transistors are not conducting when powered on, so something has to be done to get it to start. A sharp transient is needed to get it going. I haven't had time to work further with it since last month.
The obvious solution is this one. It's so glaringly simple that it's impossible to ignore. The 2N7000 is so cheap - $16 a hundred - and the circuit is so simple that it's poor judgment not to use them. And you can replace them with some TO-220 power MOSFETs for well under a dollar each and light up LEDs at an amp or more, or if you're desperate, some automobile taillight bulbs.
That's why I'll probably forget about pursuing the BJT solution further and pull the parts oqff the protoboard when I need it.
An informative Forbes article concerning the shortage of employees in jobs like engineering and tech. Believe it or not, there are jobs out there in these jobless times that are going unfilled due to a lack of applicants.
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Joule Thief pages by Brooke Clarke
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I was perusing this author's web pages, which are very informative. Lots of good info about the technical aspects of JTs. There are lost of other stuff, including some military hardware.
I found one problem with a recommendation the author made. Here's a quote:
"If a Zener diode is connected between the Base and Emitter (cathode to emitter) it will clamp the base voltage to the Zener voltage protecting the E-B junction from breakdown."
The problem is that the zener works fine in its breakdown mode, when the reverse bias voltage exceeds its zener voltage. But when the transistor is forward biased, the voltage gets up to 0.6V, which is also the forward voltage of the zener. The zener then conducts, robbing the transistor's base of its current.
A better solution is to put a small signal diode (1N4148) in series with the base lead, cathode to base. But for a Joule Thief, this raises the base's voltage to 1.2V, which may be too high for the JT to start. For a low voltage drop, it may be best to put two or three regular small signal diodes in series, across the base to emitter, cathode to base. When the reverse voltage on the base gets to 1.2v or 1.8V, the diodes conduct, shunting the current to ground.
For a conventional JT, with a single white or blue LED and 1:1 turns ratio, the voltage at the base should never exceed the peak voltage across the LED which might approach but not exceed 5V, which is the typical emitter to base maximum reverse voltage. If the collector voltage exceeds 5V (more than one LED in series), then the number of turns of the feedback winding should be reduced so the base voltage doesn't exceed 5V. For two LEDs in series, half as many turns in the feedback winding would be a good point to start.
I followed Brooke's link to "Bob Blick's speed tests showing how LEDs and laser diodes turn one." (sic) but I saw nothing on Blick's pages about that subject.
Brooke mentions white LED phosphors, and says, "There is also a white phosphors "cap" that can be installed over a blue LED to provide diffused white light. JKL Whitecap -". If you have read my past blogs on the 24/7 tests of white LEDs that I've purchased, you know that from my experience, all white LEDs (with the sole exception of Nichia) have a lifetime that is much, much shorter than the "100 thousand hour" claim made by almost all LED makers and sellers. The typical lifetime when run at 50% to 80% of max current is typically less than 2000 hours before they have lost half their initial brightness. This really bothers me because almost everyone assumes that the white LED will last much longer than an incandescent bulb, but it doesn't! ~ Perhaps this white phosphor cap will last a longer time than the typical LED.
Here's another JT circuit, from someone who has apparently collaborated with Brooke. Unfortunately the circuit uses a 10 ohm resistor to sense the LED current, and that causes a lot of power to be wasted in heating the resistor. This resistor could be reduced to 1 to 3 ohms and still do its job and yet waste a lot less power. This is done by 'prebiasing' the base to a half volt so that the current sense resistor only needs 0.1 volt drop to turn on the current limiting. I'll have to experiment with it later.
In Brooke's links I found a link to a Chinese LED maker that admits that white LEDs have a limited lifetime. In the footnotes they explain how white LEDs "decline" in output. But my 24/7 tests indicate that the losses are greater than 30%, I've found losses greater than 50% after 1500 hours or so. That much loss in my thinking makes a white LED no longer useful for illumination. Also, this Chinese maker sells 'cut-rate' LEDs for cheap toys, etc, and most other types including 1W, 3W and 5W power LEDs. They take Paypal, but there are minimum order and surcharges, so check their pricelist.
Back to experimenting...
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I was perusing this author's web pages, which are very informative. Lots of good info about the technical aspects of JTs. There are lost of other stuff, including some military hardware.
I found one problem with a recommendation the author made. Here's a quote:
"If a Zener diode is connected between the Base and Emitter (cathode to emitter) it will clamp the base voltage to the Zener voltage protecting the E-B junction from breakdown."
The problem is that the zener works fine in its breakdown mode, when the reverse bias voltage exceeds its zener voltage. But when the transistor is forward biased, the voltage gets up to 0.6V, which is also the forward voltage of the zener. The zener then conducts, robbing the transistor's base of its current.
A better solution is to put a small signal diode (1N4148) in series with the base lead, cathode to base. But for a Joule Thief, this raises the base's voltage to 1.2V, which may be too high for the JT to start. For a low voltage drop, it may be best to put two or three regular small signal diodes in series, across the base to emitter, cathode to base. When the reverse voltage on the base gets to 1.2v or 1.8V, the diodes conduct, shunting the current to ground.
For a conventional JT, with a single white or blue LED and 1:1 turns ratio, the voltage at the base should never exceed the peak voltage across the LED which might approach but not exceed 5V, which is the typical emitter to base maximum reverse voltage. If the collector voltage exceeds 5V (more than one LED in series), then the number of turns of the feedback winding should be reduced so the base voltage doesn't exceed 5V. For two LEDs in series, half as many turns in the feedback winding would be a good point to start.
I followed Brooke's link to "Bob Blick's speed tests showing how LEDs and laser diodes turn one." (sic) but I saw nothing on Blick's pages about that subject.
Brooke mentions white LED phosphors, and says, "There is also a white phosphors "cap" that can be installed over a blue LED to provide diffused white light. JKL Whitecap -". If you have read my past blogs on the 24/7 tests of white LEDs that I've purchased, you know that from my experience, all white LEDs (with the sole exception of Nichia) have a lifetime that is much, much shorter than the "100 thousand hour" claim made by almost all LED makers and sellers. The typical lifetime when run at 50% to 80% of max current is typically less than 2000 hours before they have lost half their initial brightness. This really bothers me because almost everyone assumes that the white LED will last much longer than an incandescent bulb, but it doesn't! ~ Perhaps this white phosphor cap will last a longer time than the typical LED.
Here's another JT circuit, from someone who has apparently collaborated with Brooke. Unfortunately the circuit uses a 10 ohm resistor to sense the LED current, and that causes a lot of power to be wasted in heating the resistor. This resistor could be reduced to 1 to 3 ohms and still do its job and yet waste a lot less power. This is done by 'prebiasing' the base to a half volt so that the current sense resistor only needs 0.1 volt drop to turn on the current limiting. I'll have to experiment with it later.
In Brooke's links I found a link to a Chinese LED maker that admits that white LEDs have a limited lifetime. In the footnotes they explain how white LEDs "decline" in output. But my 24/7 tests indicate that the losses are greater than 30%, I've found losses greater than 50% after 1500 hours or so. That much loss in my thinking makes a white LED no longer useful for illumination. Also, this Chinese maker sells 'cut-rate' LEDs for cheap toys, etc, and most other types including 1W, 3W and 5W power LEDs. They take Paypal, but there are minimum order and surcharges, so check their pricelist.
Back to experimenting...
Wednesday, June 17, 2009
2009 June 17 - Half way through the month
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On occasion I go by the switchyard in Orange, on Tustin Ave and Taft. This is a big switchyard, taking up more than a city block. The high voltage lines coming into this yard are from out in the desert, probably from Hoover Dam and Lake Mead. I've followed them using Google maps or Wikimapia, and they go through the desert to a big switchyard near the Calif.-Nevada border.
People go by this every day, and don't realize that just one of these super high voltage lines can power almost half of Los Angeles. The various generating sites such as San Onofre Nuclear Generating Station, Hoover Dam, the steam power plants on the coast by El Segundo and the Los Angeles Airport, and the steam generating plants on the coast near Huntington Beach are tied together to this grid of power lines. It's very interesting, because when the power goes off, you suddenly find out how much it affects your life. Wow, you grope around in the dark trying to find a flashlight. You reach for that remote but it doesn't do anything! Surprise! Your life depends on electricity.
Measuring Current
Experimenters don't realize rhat they are making inaccurate measurements and not getting the best performance from their circuit that runs from a 1.5 volt battery. The culprit is the digital multimeter they're using on the milliamp or amp ranges. The meter's internal resistance drops up to 200 millivolts or 0.2V
Two tenths of a volt drop is only 1 percent of a 20 V supply voltage, and can be ignored. But it's 13.3 percent of a 1.5 V battery, and that's a lot of loss. It's as if you removed the 1.5V alkaline battery and put in a 1.3V rechargeable, and with that low a voltage, there will be a very noticeable loss in performance. Try this. with the meter in series with the battery, and the LED lit, put a jumper across the meter, and watch the LED get noticeably brighter.
The other problem is the meter causes the readings to be in error. With the lower voltage and current caused by the meter's voltage drop, the performance of the circuit measures less. If the voltage is 13.3 percent lower and the current is also 13.3 percent lower, the circuit will be operating at 75 percent power, or about 25 percent drop in input power. This assumes that the load is purely resistive. But an active circuit such as a Joule Thief may draw less than 25 percent since it is not a pure resistance, thus the performance drop may be more noticeable.
Solution
The solution is to not use the meter's current ranges. Instead, put a low value resistor in series with the battery or power supply lead. The value should be low so that the drop will be much less than 0.2V, preferably below 0.05 V or 50 millivolts. For a typical Joule Thief that draws 100 milliamps, this would be 1/2 ohm. Lower drop would be better, provided it doesn't cause the meter readings to lose accuracy. A 100 milliamp current would measure 10 millivolts across a 0.1 ohm resistor. A typical DMM might be able to measure 10 millivolts to the nearest 0.1 millivolt, which may not be very accurate. But it's still better than losing performance due to excessive voltage dropped across the meter's resistance.
How to Make a Low Value Resistor
I make my own 0.1 ohm resistors. I use an 8 inch length of 32 AWG solid enameled wire. The actual length for 0.1 ohm is 7.4 inches, which leaves about a quarter inch on each end to wrap around and solder. I wind it on a 1 watt resistor, any value of a few hundred ohms or more. I coat the wires with liquid tape or lacquer (nail polish works okay). These measure very close to 0.1 ohm with my H-P 3478A DMM in the 4-wire ohms measuring mode.
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On occasion I go by the switchyard in Orange, on Tustin Ave and Taft. This is a big switchyard, taking up more than a city block. The high voltage lines coming into this yard are from out in the desert, probably from Hoover Dam and Lake Mead. I've followed them using Google maps or Wikimapia, and they go through the desert to a big switchyard near the Calif.-Nevada border.
People go by this every day, and don't realize that just one of these super high voltage lines can power almost half of Los Angeles. The various generating sites such as San Onofre Nuclear Generating Station, Hoover Dam, the steam power plants on the coast by El Segundo and the Los Angeles Airport, and the steam generating plants on the coast near Huntington Beach are tied together to this grid of power lines. It's very interesting, because when the power goes off, you suddenly find out how much it affects your life. Wow, you grope around in the dark trying to find a flashlight. You reach for that remote but it doesn't do anything! Surprise! Your life depends on electricity.
Measuring Current
Experimenters don't realize rhat they are making inaccurate measurements and not getting the best performance from their circuit that runs from a 1.5 volt battery. The culprit is the digital multimeter they're using on the milliamp or amp ranges. The meter's internal resistance drops up to 200 millivolts or 0.2V
Two tenths of a volt drop is only 1 percent of a 20 V supply voltage, and can be ignored. But it's 13.3 percent of a 1.5 V battery, and that's a lot of loss. It's as if you removed the 1.5V alkaline battery and put in a 1.3V rechargeable, and with that low a voltage, there will be a very noticeable loss in performance. Try this. with the meter in series with the battery, and the LED lit, put a jumper across the meter, and watch the LED get noticeably brighter.
The other problem is the meter causes the readings to be in error. With the lower voltage and current caused by the meter's voltage drop, the performance of the circuit measures less. If the voltage is 13.3 percent lower and the current is also 13.3 percent lower, the circuit will be operating at 75 percent power, or about 25 percent drop in input power. This assumes that the load is purely resistive. But an active circuit such as a Joule Thief may draw less than 25 percent since it is not a pure resistance, thus the performance drop may be more noticeable.
Solution
The solution is to not use the meter's current ranges. Instead, put a low value resistor in series with the battery or power supply lead. The value should be low so that the drop will be much less than 0.2V, preferably below 0.05 V or 50 millivolts. For a typical Joule Thief that draws 100 milliamps, this would be 1/2 ohm. Lower drop would be better, provided it doesn't cause the meter readings to lose accuracy. A 100 milliamp current would measure 10 millivolts across a 0.1 ohm resistor. A typical DMM might be able to measure 10 millivolts to the nearest 0.1 millivolt, which may not be very accurate. But it's still better than losing performance due to excessive voltage dropped across the meter's resistance.
How to Make a Low Value Resistor
I make my own 0.1 ohm resistors. I use an 8 inch length of 32 AWG solid enameled wire. The actual length for 0.1 ohm is 7.4 inches, which leaves about a quarter inch on each end to wrap around and solder. I wind it on a 1 watt resistor, any value of a few hundred ohms or more. I coat the wires with liquid tape or lacquer (nail polish works okay). These measure very close to 0.1 ohm with my H-P 3478A DMM in the 4-wire ohms measuring mode.
Thursday, June 04, 2009
Joule Thief uses TV color convergence coil
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I built this two transistor, single winding Joule Thief quite a while ago, and I remodeled it with a 0.5W multichip white LED and a few other changes. The original coil gave 56 mA LED current when I adjusted the base bias resistor to 44k, and the half watt LED was running nice and bright. I then changed the coil to the red winding of a TV color convergence coil I had in my junkbox, just because it looked cool. Obviously it was for the red gun on the CRT.
After many years the old timer finally has a purpose in its life. But the red coil has too high a DC resistance, so the LED isn't very bright, current is just a few mA. It's doubtful that you will ever see one of these again, because in the last few years, CRTs have all but disappeared, replaced by LED flat panel displays.
The circuit uses two BC338 transistors. I've uploaded the schematic, check it out.
Back to experimenting....
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I built this two transistor, single winding Joule Thief quite a while ago, and I remodeled it with a 0.5W multichip white LED and a few other changes. The original coil gave 56 mA LED current when I adjusted the base bias resistor to 44k, and the half watt LED was running nice and bright. I then changed the coil to the red winding of a TV color convergence coil I had in my junkbox, just because it looked cool. Obviously it was for the red gun on the CRT.
After many years the old timer finally has a purpose in its life. But the red coil has too high a DC resistance, so the LED isn't very bright, current is just a few mA. It's doubtful that you will ever see one of these again, because in the last few years, CRTs have all but disappeared, replaced by LED flat panel displays.
The circuit uses two BC338 transistors. I've uploaded the schematic, check it out.
Back to experimenting....
Sunday, May 31, 2009
June 1st (almost), Blue Blinky Update, etc.
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Running LEDs Off a Super Capacitor Bank
I left a message in Energetics forum about how to drive an LED from a bank of super capacitors. I'm trying to come up with a solution to the following problems. I have solar cells that put out about 4 volts. I'm using them to charge a bank of four super capacitors up to 4 volts. Problem is that when the JT voltage gets up to the LED's forward voltage or about 3 volts, the LED starts to conduct. But the only thing between the LED and the battery is the winding of the coil, which is very low resistance. The current through the LED can get so high it will damage the LED.
I think the problem of the LED conduction at input voltages over 3 volts can be solved by putting two LEDs in series to raise the total forward voltage to over 6 volts. But that still leaves the wide input voltage problem.
This slow discharging of the super capacitor bank means that I need a circuit that will accept a wide range of input voltages, anywhere from 4 volts down to 1 volt, and will put out about the same current to the LED over this range. A conventional JT will put out LED current that varies with the input voltage; low input voltage will give low LED current. I think I may be able to compensate for the change in input voltage by increasing the JT base bias as the input voltage decreases. I'll have to try this on a JT.
Actually, I'm not so concerned about the LED current tapering off as the input voltage decreases, I'm concerned that the LED current will be too high at the highest input voltage. If the LED current stays somewhat steady as the input voltage increases above 3 or so volts, it would be okay if the current drops off somewhat below 2 volts. Why not? It will help extend the time that light will be available.
BLUE BLINKY MONTHLY UPDATE
Tomorrow will be the first of the month, and it will be a year and a half - 18 months - since I put the partially depleted AA cell into the blue blinky's battery holder and it started to blink 24/7. It's dim but still blinking. For the last several months the AA cell's voltage has been stuck at about 0.78 volts, with little if any sign of decreasing. This month it measures ... 0.784 volts, not surprising since that's about what it was last month and the month before, but totally surprising in that it hasn't decreased in months. It seems the battery and circuit are at a point of equilibrium where one draws only as much as the other can put out.
More to follow.
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Running LEDs Off a Super Capacitor Bank
I left a message in Energetics forum about how to drive an LED from a bank of super capacitors. I'm trying to come up with a solution to the following problems. I have solar cells that put out about 4 volts. I'm using them to charge a bank of four super capacitors up to 4 volts. Problem is that when the JT voltage gets up to the LED's forward voltage or about 3 volts, the LED starts to conduct. But the only thing between the LED and the battery is the winding of the coil, which is very low resistance. The current through the LED can get so high it will damage the LED.
I think the problem of the LED conduction at input voltages over 3 volts can be solved by putting two LEDs in series to raise the total forward voltage to over 6 volts. But that still leaves the wide input voltage problem.
This slow discharging of the super capacitor bank means that I need a circuit that will accept a wide range of input voltages, anywhere from 4 volts down to 1 volt, and will put out about the same current to the LED over this range. A conventional JT will put out LED current that varies with the input voltage; low input voltage will give low LED current. I think I may be able to compensate for the change in input voltage by increasing the JT base bias as the input voltage decreases. I'll have to try this on a JT.
Actually, I'm not so concerned about the LED current tapering off as the input voltage decreases, I'm concerned that the LED current will be too high at the highest input voltage. If the LED current stays somewhat steady as the input voltage increases above 3 or so volts, it would be okay if the current drops off somewhat below 2 volts. Why not? It will help extend the time that light will be available.
BLUE BLINKY MONTHLY UPDATE
Tomorrow will be the first of the month, and it will be a year and a half - 18 months - since I put the partially depleted AA cell into the blue blinky's battery holder and it started to blink 24/7. It's dim but still blinking. For the last several months the AA cell's voltage has been stuck at about 0.78 volts, with little if any sign of decreasing. This month it measures ... 0.784 volts, not surprising since that's about what it was last month and the month before, but totally surprising in that it hasn't decreased in months. It seems the battery and circuit are at a point of equilibrium where one draws only as much as the other can put out.
More to follow.
