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Old 06-21-2013, 04:54 PM   #167
Hoppy
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While experimenting with putting 3 photodiodes in one sensor, in order to improve the spectral sensitivity of the PAR meter, I found that I could fit a photodiode into a 1/2" diameter acrylic tube. This led me to redesign the one diode PAR meter to be 2/3 the size of what I had been making - a 1/2" diameter vs. 3/4" diameter sensor.


Assembling this is much easier if you make a simple fixture to hold it while you work on it, while also keeping the photodiode located where it should be. This is just a piece of 3/8" tube, with a longitudinal saw kerf in one side, to make it fit inside a 1/2" acrylic tube easier, with a length sticking above the base equal to the desired distance from the top of the 1/2" tube housing to the top of the photodiode (9/32 inch), cemented into a sheet of acrylic.

Fit the 1/2" tube housing on the assembly fixture, and poke the electric cable through the hole, and up out of the housing far enough to let you strip the insulation about 1/4" back. Don't do this before trying to stick the cable through the hole - it is much easier to do before stripping the wires.


After stripping the wires, gently move the cable back so the stripped wires are inside the housing.


Now, look at the face of the photodiode and locate the mark, either a "+" or just a dot, which identifies the cathode of the diode. This is the lead that connects to the red wire in the cable. Turn the housing over and carefully drop the diode in, so the leads straddle the cable, with the cathode lead on the red wire side. Put the housing back on the fixture, so the diode rests on the top of the stub of tube in the fixture. Use a wood toothpick or something similar to bend up the wires to get them in contact with the diode leads, ready to solder the connections.


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