On May 11, 2025 I finished building my diode sorting fixture using a LM317 constant current source. In the fixture is a 1N4003 diode being tested today on May 29, 2025. On the 11th I sorted 100 1N4148 diodes for future use in Diode Ring Mixers. From that sorting I got 16 batches of 4 diodes matched and 5 batches of 2 diodes matched. Once I started the process it didn't take long and it was well worth it! For the 1N4148 diodes my measured forward voltage was from .714 to .729 vdc.
Whenever I go to hamfests or thrift stores, I like to look for cheap enclosure possibilities. After gutting the parts inside I repurposed this mouse controller case I bought several years ago. I owe credit for this project to "M0NTV Homebrewing" youtube channel. Nick M0NTV did a great job on explaining how to design and build a constant current source for diode sorting using the LM317 regulator.
https://www.youtube.com/watch?v=EkMpLKwNl2U
I decided to leave out the variable pot. Like Nick I planned my circuit to use about 10mA constant current. I used 2 64 ohm resistors in series to get 124 ohms and provide 10 mA of constant current. I adjusted my power supply to provide 5.24 vdc to the fixture.
Here are the parts I used to build the fixture:
LM317T - Tayda - A-177 - $.23
4-40x 1/4" machine screw and nut (to mount LM317T)
.1uF - A5E104 - junkbox - $.00
51 ohm - Mouser - 271-51-RC -
1K - linear pot - Tayda - A-1962 - $.50
enclosure - used from Ohio Thrift store - $4.99
2 Red Binding Post - Tayda - A-3583 - $.25 ea
2 Black Binding Post - Tayda - A-3908 - $.25 ea
DC 2.1mm Jack DC-099 - Tayda - A-5245 - $.55
DC Power Cable 12V5A - 2.1mm - Centro Power - B07C7VSRBG - $.46
I enjoyed building another piece of test gear for the lab. Good luck on your build if you choose to make a diode sorting fixture.
73,
Alan, N8WQ
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