White LEDs were the technological breakthrough that changed the world of lighting, now they are everywhere. There’s no better sign of their cost-effective ubiquity than the dollar store solar garden light: a complete unit integrating a white LED with its solar cell and battery storage. Not content with boring white lights on the ground, [Emily] decided to switch up their colors with a mix of single-color LEDs and dynamic color-changing LEDs, then hung them up high as colorful solar ornaments.
The heart of these solar devices is a YX8018 chip (or one of its competitors.) While the sun is shining, solar power is directed to charge up the battery. Once the solar cell stops producing power, presumably because the sun has gone down, the chip starts acting as a boost converter (“Joule thief”) pushing a single cell battery voltage up high enough to drive its white LED. Changing that LED over to a single color LED is pretty straightforward, but a color changing LED adds a bit of challenge. The boost converter deliver power in pulses that are too fast for human eyes to pick up but the time between power pulses is long enough to cause a color-changing circuit to reset itself and never get beyond its boot-up color.
The hack to keep a color-changing LED’s cycle going is to add a capacitor to retain some charge between pulses, and a diode to prevent that charge from draining back into the rest of the circuit. A ping-pong ball serves as light diffuser, and the whole thing is hung up using a 3D-printed sheath which adds its own splash of color.
Solar garden lights are great basis for a cheap and easy introduction to electronics hacking. We’ve seen them turn into LED throwies, into a usable flashlight, or even to power an ATTiny microcontroller.
Continue reading “Give Your Solar Garden Lights A Color Changing LED Upgrade”
Solar garden lights are just another part of the great trash pile of our age, electronics so cheap as to be disposable. Most of you probably have a set lurking somewhere at home, their batteries maybe exhausted. Internally though they are surprisingly interesting devices. A solar cell, a little boost converter chip, and a little NiCd battery alongside the LED. These are components with potential, as [Randy Elwin] noted with a mind to his ATtiny85 projects.
The YX805A chip he references in his write-up is one of several similar chips that function in effect as joule thieves, extending the available charge in the battery to keep the LED active as long as possible when their solar panel is generating nothing, and turning it off in daylight when the panel can charge. Their problem is that they are designed as joule thieves rather than regulators, so using them as a microcontroller PSU without modification can result in overvoltage.
His solution is to use the device’s solar panel input as a feedback pin from his ATtiny, allowing the microcontroller to keep an eye on its supply voltage and enable or disable the converter as necessary while it keeps running from the reservoir capacitor. Meanwhile the solar panel now charges the NiCd cell through a single diode. It’s not perfect and maybe needs a clamp or something, he notes that there is a condition in which the supply can peak at 8 volts, a level which would kill an ATtiny. But still, we like simple hacks on dollar store parts, so it’s definitely worth further investigation.
This isn’t the first garden light hack we’ve shown you, there was this flashlight, and some LED hacks.
Solar light picture: Leon Brooks [Public domain].