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Registered Member #202
Joined: Sat Feb 18 2006, 07:20AM
Location:
Posts: 3
Just for fun, I tried this with a large TO-36 case germanium power transistor. I didn't want to dig out a power supply so I just used two and then three 9v batteries in series to bias the junction. I did not get any light output or maybe I could not see it. So maybe a Silicon only thing or possibly I wasn't using enough current. I will try again with more power later. I also hooked the junction across my mutimeter and exposed it to light and got slight phototransistor effect (drop in junction resistance when exposed to bright light).
Another thought... I have a very old (like 1970 or so) power photodarlington (pic below with his friend the mangled germanium transistor) that looks like a standard power transistor with no lid. It is a germanium device but the junctions are potted with rose colored translucent plastic. It says in the data sheet that the rose colored plastic is to filter out ambient IR light as it would destroy the junction.
It still worked last time I was playing with it so apparently the rose plastic works. Also pictured below is a very clever and very simple little self holding shooting gallery target that came with this photodarlington (called a photomultiplier) on the package. You could make this with any modern photo-transistor that would handle the current from bulb or LED. The basic idea is that you hit the phototransistor with a light which in turn switches it on and turns on the bulb and then the light from the bulb shines on it and holds it on. Very good for kids (or adults) shooting gallery games. Fun to build with LED AND pizeo buzzer. Also can be triggered with laser pointer. Gives you sense of power to aim pointer and make annoying beeeeeeeeeep sound happen like magic. Man I have gone completely off topic now.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
What photographic setup are you using. You are getting a lot of magnification.
Nikon D70 and a 150 mm 1:1 Macro lens. The focal length does not affect the magnification only the distance you get that magnification on. The CCD chip in the D70 is about 22 mm wide so with a 1:1 macro lens an object that is 22 mm wide would fill the whole frame. To get larger magnification you need to add lens rings beween the lens and the camera to make it possible to focus on shorter distances.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
I wonder if this would work with the junction under water. this would exclude air (as someone mentioned before) and would act as a good heat sink as soon as the temperature reached 100C. (my 1st post on the new improved forum BTW).
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Worlds most inefficient LED
