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Re: [OM] circuit to measure shutter speed

Subject: Re: [OM] circuit to measure shutter speed
From: Chuck Norcutt <norcutt@xxxxxxxxxxxxx>
Date: Sun, 13 Feb 2000 07:56:30 -0500
Tim Hughes asked:
I don't know if you are using photovoltaic cells or phototransistors or
CDS cells?
----------------------
Phototransistors bought at a small shop for about $2 each.  The one I
used has a wide angle lens and the one in reserve a narrow angle lens. 
I'm pretty sure the biggest problem is not having a DC light source. 
I've also tried it with daylight but an incandescent lamp was probably
still contributing to what the detector saw.  As it is, it still works
OK for 1/60 and slower where an error of 1-2 milliseconds doesn't matter
much.  Timing is via a little Quick Basic program which needs to be run
in DOS mode or under real DOS to keep Windows from trying to multi-task.

I should be a little smarter now if I ever find the time to get back to
it.  BTW, it was easy to make.  I used a 15-pin D connector plugged into
the joystick port.  The phototransistor acts as  one of the four
joystick push buttons.  The joystick port provides the power so the only
other part required is a 100K resistor which is a normal part of the
pushbutton circuit.  Presumably, one could use up to four
phototransistors to make a more sophisticated device.

Chuck Norcutt
Woburn, Massachusetts, USA

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