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  1. #11
    bvy
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    So I built this device to spec -- AA battery, phototransistor recovered from an old mouse, and a mono jack. I'm trying it on my PC now using Audacity software, and it just barely responds to light. To make sure I assembled it properly, I connected my voltmeter up to each contact on the mono plug, and shined a light at it. The meter pegged. Is there some way to boost the signal? Another design I saw was the same except that it added a 4.7k resistor. Will that help?

  2. #12
    BetterSense's Avatar
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    You should be able to get the voltage to swing from 0 up to the maximum battery voltage between light and dark. If it doesn't do that, you need to adjust your resistor values. You could try using a higher voltage battery. I used a 9v for mine.
    f/22 and be there.

  3. #13
    bvy
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    Thanks. I'll try with a nine volt battery. As I mentioned, I don't have a resistor on the the circuit. So it sounds like I should add one?

  4. #14
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    Yes, typically you go from positive terminal, to the short leg of the photodiode, and from the long leg of the photodiode, into a resistor, and from that, back to the battery. You tap your output off between the photodiode and the resistor, and run that to your soundcard or whatever. The value of the resistor determines the sensitivity of the thing, so using a pot is a good idea. If the resistor is small, very small voltage will be developed when the photodiode is illuminated even with a bright light. If the resistor is very large, the full battery voltage may be developed even in room lighting, and the voltage will never go back down to zero.
    f/22 and be there.

  5. #15

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    Make sure that your aperature is open enough to transmit a signal and adjust your input signal (mike input) in Audicity to at least 50% ot higher if you need it.That slider seems to default to a very low value but you should be able to increase it enough to see your waveform at any amplitude that you like.Ron G

  6. #16
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    I just found the need for a shutter speed tester. Found this thread and some others in other sites. There's a guy in Romania I think it is, who has designed a low cost shutter speed tester. He's got an entry level model that's only $14.99 on eBay. That one works like with the Audacity program. Then he has a model that doesn't need a computer at all, it has all the electronics inside. Those go for $99 without a light source and $119 with a light source. I think I'm going to buy one of these rather than build one myself.

    On eBay, look for seller by the name "vfmoto" if you're interested.
    I love the wilderness and I love my trail cameras, all Fuji's! :) GA645, GW690 III, and the X100 which I think is the best trail camera ever invented (to date).

  7. #17
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    This all sounds pretty easy, at least easy enough that I can probably do it! Thanks to every who shared above.

  8. #18

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    I just put the lens next to my laptop, turn on audacity and fire the shutter. You'll see large spikes where it opens and closes.

  9. #19

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    Quote Originally Posted by alexhill View Post
    Saw this on one of the blogs I follow (hackaday.com) and thought it was pretty awesome. http://www.rusted.free.fr/speed%20tester.html
    Seems like I've been asking a lot of questions lately, for which I thank you guys. OK, another one: I intend to fabricate the tester in the referenced link to test my old 5-speed Betax. Now my thinking or logic might be flawed here, but it seems to me on an iris shutter, the shutter is open for less time on the edges of the round opening than the center, right? The shutter takes time to open and close, nothwithstanding the time it stays open. The edges are the last to be un-covered, and the first to be re-covered, right?. So if I make my tester with the phototransistor just a couple inches away from the rear lens element, it seems like I'd get a false reading. Seems like the phototransistor would have to be at the film plane to get a true reading. Feel free to correct my logic. Thanks.

  10. #20
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    If you shut down to f16 your opening is quite small so not really an issue, anyway your measuring the time light is hitting the film so as soon as the shutter opens light is coming through the hole so you measure time open to time close. With the photo transistor distance I only think it would be out by the percentage of the speed of light to cover the extra distance is photo transistor is away.

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