Computer-based shutter speed tester

Circuit diagram and description

The circuit is very simple requiring only 5 components. It could be a lot more sophisticated but this does the job and most people who can turn on a soldering iron can build it.

The theory behind is fairly simple.

• The parallel port is fast and this means that the output is minimally influenced by transmission etc.
• By using the clicks of the Intel processor, timing can be accurate - claimed at the nonsecond level.
• The power is supplied from the computer so you can have a simple circuit without batteries.
• The sensitivity of the photodiode can be controlled.

The software monitors the Status lines to see if line 15 changes. When light hits the photodiode(the shutter opens) , it changes the status of 15 via the BC212 transistor. The timing starts. When the light is cut off (the shutter closes) the timing stops and the software presents the result on the computer screen.

The circuit is tuned by adjusting the variable resistor to accommodate the level of light your are providing at the front of the camera - the more light the better.

All the Data line is doing is providing a power source for the Photodiode.