The old homemade shutter tester.
I want to do the old DIY soundcard shutter tester originally presented here. Digging around I found this little snippet at http://medfmt.8k.com/mf/shutterspeed.html on how to make the readings more readable at high speeds.
I haven't done much with circuits in a long time, would some one be able to translater how that into a scematic for me?
I have the phototransistor in series with a 4K resistor and 1.5 volt cell, and take the output from across the 4k resistor. I run this output signal through a 3900 pF capacitor to the mike input of the sound card. the resulting voltage spikes that occur when the shutter opens (negative-going) and then closes (positive-going) are now so quick and widely separated and it is easy to pinpoint the exact times of each event
I should note that I want to build this to test the Focal Plane shutter on my Speed Graphic, so I have an idea this idea in my head. What Id like to do is build two of these circuits, and mount them both into one old leaky filmholder I have. I'd drill two holes though it too mount the two sensors, one at the top, and one at the bottom. This way I could measure any slow down as the shutter travels. I haven't noticed any horrible effects of any, but I'm a geek and want to know if it is there, and how much it is. :p Also, I'd keep the darkslide in closest to the shutter, and drill small holes into it lining up with the photosensors, to get rid of any light coming from elsewhere(like the rest of the huge shutter slit) from messing up the readings.
And major flaws with this logic that I'm missing? Ideas for improvement?