The next time you buy a disposable camera, ask for it to be returned to you when the store develops the film.Īlternatively you can ask the store to save the next unit that comes in for development - after all, they throw the units away!įor this project, all you need is a flash unit and two extra components - a BD 679 transistor and a high speed diode. (For a discussion on transistor pin-outs, and finding if the transistor is PNP or NPN, go to: transistor pin-outs. Well, now you can take advantage of this and pull apart a USED camera. It seems such a waste, to throw away a complete high-voltage flash unit, but that's the cost of progress. With a little bit of fore-thought, manufacturers could have made the camera re-loadable, but that would defeat the purpose of disposability! For less than $20 you get a pre-loaded camera with a flash! It's absolutely amazing technology, but what a waste of resources! After 12-27 flashes, you throw away the camera and a perfectly good flash unit. Every supermarket, photographic store and corner shop has them near the check-out counter. It costs less than $3.00, contains six BUILDING BLOCKS, re-cycles a disposable flash camera and you are going to learn a lot about electronics.Įveryone has seen a disposable flash camera. You may want a good Cap across the supply, but may not be essential.
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These estimates also depend on LED, PNP and 6V characteristics for internal series resistance at operating current.
If 6V=>6.5V we get I = 2.0V/4.5 = 440mA You can choose the nearest value of R. The accuracy of the 6V will affect the current. The drop across the Darlington will be around 1.2V when ON leaving the difference across your current limiting resistor of 1.5V. The PNP will need much more current gain so choose a Darlington that can handle 500mA with 1W dissipation derated to 50%. In order to drive a 1 Watt LED such as white, it needs around 330mA 3.3V. A red LED can be 2.0 -> 2.2V, a green LED can be 2.4 -> 2.7V and white and blue LEDs are even higher. That may be the drop for a typical silicon diode but the LED will be greater. The forward voltage drop across the LED will not be 0.7V. Lowering the capacitance and/or resistance will make it cycle faster The cycle time will be a function of the 10u capacitor and 22R. 2.0v (approximate) drop across a red LED ( blue may be up to 3.3v) - 0.2v drop across the collector/emitter transistor junction A " Darlington pair " of transistors has a much higher gain and can be used for higher-current applications. make sure the PNP transistor is also rated for the current. Lowering the resistance value will increase the current and thus brightness. The current through the LED is limited by the "22R" resistor.
I need to get this circuit or a very similar one to FULLY power optionally a 1/2 watt LED or 2 half watt LEDs, so from 120ma to 240ma, depending on resistors. Apparently I have not fully grasped the dynamics at work in how/why Q1 shuts off and why the Darlington has changed this. I tried a few changes of resistors but no luck. Apparently for some reason the discharge of the electrolytic does not drop the voltage low enough to turn off Q1 let alone keep it off for any length of time. Ĭircuit LED FLASHER theory : when the BC557 PNP is replaced by the Darlington the circuit powers the LED up slowly (too slow) then it fails to shut off. We tried using a couple of different Darlington transistors (the one on the breadboard now is a Fairchild Transistors Darlington PNP Epitaxial Sil US HTS:8541408000 ECCN:EAR99. Is it possible or possible to use some variation on this? I also need to be able to manage or set the strobe rate. We must be able to run either this circuit or one that does the same thing but with a 1/2 watt or 1 watt LED.
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