Multiple diodes can be driven by the same power supply as long as they are connected in series, but they must never be connected in parallel. I suspect/hope this is some fairly straightforward concept - but if the battery is sitting as it is, everything works well and these are fairly low-power devices, all connected in parallel - I don't. The laser diodes are connected backwards in the posted schematics, and there are no current limiting resistors in series with the optoisolator inputs, as is required. An important consideration for this practice is the current sharing between diodes due to the difference of electrical characteristics. When two diodes are connected in series they will function properly as long as the. Although laser light is often thought of as a straight, parallel beam, the light emitted from a laser diode actually diverges to some extent as it diffracts.
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