My wife picked up a battery-powered Xmas light set, but she doesn't like the patterns the controller provides. The lights are "fairy" LED lights with two LEDs back to back in the ornament. So, 3V +- light one LED and 3V -+ lights the other.
It occurred to me that I could control the ornaments with PWM outputs into an H-bridge, not unlike controlling a motor direction and speed. I don't want to use one of my high power H-Bridge motor control boards for this, so can someone recommend a low-power H-bridge chip?
Pololu has the best selection, at very reasonable prices. Lowest current brushed DC motor driver module: https://www.pololu.com/product/2990
If it’s really just a couple of leds down in the 50mA area, you might squeak by using two arduino in pins…
At somewhat higher currents, you can do interesting things with 74ac logic gates. See things like the Z-bridge from “beam robotics”: BEAM Circuits -- Motor drivers
Above that, you can build circuits out of 4 to 6 discrete transistors. Or maybe use a couple of 555 timers (200mA) or a 556 - it depends on how much construction you want to do, and which parts you can get easily/cheaply. (Careful with 555 variants - not all have symmetric source/sink output currents.). Robotics: 555 Timer H-Bridge | Science 2.0
Also, some “gate driver” chips can be used to drive low power circuits without actually using any mosfets. Microchip used to have one whose datasheet specifically mentioned using it by itself for small motors, but I’m having trouble finding it now…
I don't see how. It's two wires feeding back-to-back LEDs, so I have to reverse the polarity. Which is why an H-bridge chip comes to mind.
I could easily use 555's like in the Robotics article you linked, but that's all the controller does. That's what she wants replaced.
I assembled our outside decorations and inside tree on programmable LEDs using FastLED, and this year WLED. She wants that kind of smooth control so PWM into an H-bridge is what I am thinking.
It looks like the L9110 will do the job, so it's a choice of $$7 each at Amazon or 50¢ from China. I think I will just order the parts from China and tell my wife: "Next Christmas".
Before I go looking for a CMOS buffer IC with 50 mA capability, I want to know how you are certain it requires only 50 mA. That sounds remarkably conservative though I suppose any more and the AA batteries would not last long.
If it is just ±50 mA, then three gates in parallel of a 74HC04 for each driver line would seem plausible.
Thanks- I hadn't thought of parallel buffers. But, I solved the problem by rewiring the ornament with 5V programmable LED strings and a Wemos D1 Mini. (Happy wife was the goal- nailed it).
To light LED1, you output LOW to D4 and HIGH to D5. To "reverse the polarity" and light LED2, set D5 LOW and D4 HIGH. It's a standard technique, and works on any sort of output that has both source and sink capability. See also "Charlieplexing", which uses the third available state ("Input") to drive N*(N-1) LEDs from only N pins. ( https://www.instructables.com/How-to-drive-a-lot-of-LEDs-from-a-few-microcontrol/ )
If it were just one pair of LEDs, then no problem using two data ports, but the string is ten back-to-back pairs of LEDs. No way a GPIO pin will supply enough current for ten LEDs.
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