Bicolor THT LED with four separate pins -- or alternative idea? - Page 1
Forum section: electronics / projects

author: ebastler
author_rank: Super Contributor
timestamp: October 07, 2024, 06:33:57 am
content: For a hobby project (which will hopefully be of interest to a few others, so should be reasonably easy to build) I am looking for a bi-color LED to indicate battery charging and power-on state. The two LEDs can't share any terminals: One sits between the external power supply and the charging IC's "charging now" output, the other between the switched internal supply voltage and ground.While I found various bicolor LEDs in SMD packages which bring out the two anodes and two cathodes separately, I came up empty looking for THT parts. Has anyone come across such a beast?I would prefer THT since it gives me more flexibility in positioning the LED, bringing it to the same height over the PCB as the switch and jack next to it. (It would be bent 90° to face a side wall of the enclosure.) I could use an SMD LED with an angled light guide to bring the light out to the side, but the off-the-shelf light guides don't have the right heights.Any other ideas? Have you been successful making your own 90° light guides, so they could be "cut to size"? (I have used straight polycarbonate rods with good success, but assume a sharp bend will make them lose most of the light.) Maybe there are off-the-shelf light-guide prisms which can be glued to the enclosure instead of being mounted on the PCB, so they sit at the desired position? Or some DIY solution which uses two separate THT LEDs and combines their light?Many thanks for your input!

author: Analog Kid
author_rank: Super Contributor
timestamp: October 07, 2024, 06:39:30 am
content: Dunno if this'll help, but I have successfully cut down through-hole LEDs (for model railroad purposes) by grinding with a Dremel. You can get really really close to the active element before the magic smoke escapes. Maybe you could grind two of 'em side-by-side and glue them together?Of course this will change the light dispersion, but maybe you can fix that somehow.

author: Ian.M
author_rank: Super Contributor
timestamp: October 07, 2024, 07:10:39 am
content: Hmm . . .Assuming there is a common ground, what about adding an optocoupler, opto's LED in place of the charging LED to drive a common cathode LED, cathode to ground, with the Opto's output transistor and a dropper resistor feeding it from the ext. power in? You *may* even be able to simply use a PNP transistor, emitter to ext, power in, instead of the optocoupler.As to the light guides, a swept bend, with a well polished surface wont loose much light. See page 7 of:https://www-eng.lbl.gov/~shuman/XENON/REFERENCES&OTHER_MISC/Lightpipe%20design.pdfPolycarbonate is heat bendable, but must be heated slowly or preferably baked out to prevent bubbling from absorbed moisture.

author: magic
author_rank: Super Contributor
timestamp: October 07, 2024, 07:16:48 am
content: The PNP thing makes sense. One transistor, one base resistor and you can use common as dirt RGB LEDs with common cathode.Maybe you will even find a use for the third color.

author: ebastler
author_rank: Super Contributor
timestamp: October 07, 2024, 07:35:07 am
content: Thanks! I like the optocoupler or PNP idea a lot. Common-cathode LEDs are plentiful of course, both RGB and bicolor. Add one or two components to the PCB and avoid the fiddling with making a custom light guide (and then not breaking it later when installing and removing the PCB from the enclosure...)