I needed to have something to test the speed of the shutters of my cameras since many of the cameras that I buy are completly broken.

My younger brother, who just finished his telecommunications studies came out with this idea.

He suggested to use the photo transistors of an old mouse.

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Wiring diagram

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Photo transistors. There are two clear ones with a plastic cover and two red ones. One of the clear ones is used.

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I used a slide box because the with of the box is the size of a battery. The central leg and one side leg of the photo transistors are welded to one wire and the other leg is welded to the other wire. If it does not work, invert the battery.

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Play Doh! What a great invention. 

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I use "music morpher gold" to measure the signal produced by the tester. The tester is connected to the microphone plug of my computer.

SPEED MILLISECONDS
1 1000,00
1/2 500,00
1/4 250,00
1/5 200,00
1/8 125,00
1/10 100,00
1/15 66,67
1/25 40,00
1/30 33,33
1/50 20,00
1/60 16,67
1/70 14,29
1/100 10,00
1/125 8,00
1/200 5,00
1/250 4,00
1/150 6,67
1/200 5,00
1/300 3,33
1/400 2,50
1/500 2,00
1/1000 1,00

This table shows the equivalence between the tester reading and the shutter speed. The example is roughly a 1/25 speed (it's a Lomo Lubitel, not a Hasselblad!)