How to make a photocoupler

The production principle is shown in Figure 6-16 (a). The light-emitting diode uses a round red diode; the phototransistor is modified from 3A×31. 3AX31 uses a slender cap. Use a file to flatten the top of the cap, and then use a needle to carefully remove the silicone grease in the tube. Do not damage the tube core, otherwise the photosensitivity will be lost. Take another aluminum shell electrolytic capacitor, hollow it out, file off the shell top, and refer to Figure 6-16 (c). Align the light-emitting diode and phototransistor and insert them from both ends of the aluminum shell. Seal the left rear with epoxy resin glue. After curing, it can be put into use.