Mononymous maker Tim has discovered a surprise inclusion in the LED of a cheap flickering candle LED home accessory: a functional clone of the Microchip PIC12F50x eight-bit microcontroller.
"I was recently tipped off to an upgraded [LED tea-light] that includes a timer that turns off the candle after it was active for 6h and turns it on again 18h later, e.g. when you turn it on at 7PM on one day, it would stay active till 1AM and deactivate itself until 7PM on the next day," Tim explains of the feature which piqued his interest. "Seems quite useful, actually. The question is, how is it implemented? I bought a couple of these tea lights and took a closer look."
Externally, the timer-capable lights looked like any other LED-based tea-light candle: a white wax-like plastic shell and a plastic diffuser acting as the flame. Inside was a single compact LED connected to a battery through a switch — no other circuitry, and the switch simply moved one leg of the LED to make and break the contact with the battery.
What a casual inspection didn't reveal was any form of microcontroller, or even a timer. A look through a microscope at the LED, though, turned up something interest: the die of an integrated circuit which seemed over-engineered for being a simple LED. "What is curious about the IC," Tim explains, "is that it rather large, has plenty of unused pads (three out of eight used) and seems to have relatively small structures.
"There are rectangular regular areas that look like memory, there is a large area in the center with small random looking structure, looking like synthesized logic and some part that look like hand-crafted analog. Could this be a microcontroller?"
Recognizing the pad layout, Tim realized the chip was a functional clone of the Microchip PIC12F50x — a low-cost one-time-programmable eight-bit microcontroller, rather than an application-specific integrated circuit (ASIC) designed for the task. "In the year 2023, it appears that investing development costs in a candle-flicker ASIC is no longer the most economical option," Tim surmises. "Instead, ultra-inexpensive eight-bit OTP microcontrollers seem to be taking over low-cost electronics everywhere."
Tim's full write-up is available on his blog, along with observations on a surprisingly high current consumption which could be improved with a move to a sleep-mode microcontroller.