We at the moment are within the homestretch and Christmas magic is within the air! Engineers and electronics hobbyists Jeff Keacher and Sean Beever couldn’t let this hacking alternative slip by like Santa eluding curious eyes on Christmas Eve, so that they constructed a cool gadget that may pluck a few of that magic out of skinny air to unfold Christmas cheer. Their machine is an digital vacation card that makes use of ambient RF and lightweight power to mild up LEDs on a customized printed circuit board tree. Since no battery is required, this little card can maintain the Christmas cheer going lengthy after the massive day has come and gone.
To energy the machine, power is gathered from a number of sources: light-harvesting LEDs, a 2.4 GHz RF resonant circuit, or — in case you are not feeling particularly magical — a USB-C port. When out there power exceeds rapid necessities, the surplus is saved in a supercapacitor to take care of operation in periods with out exterior energy. A PIC16LF18854 microcontroller manages the interconnection between the power accumulation and power consumption voltage rails.
The RF-based power harvesting system is especially attention-grabbing, resembling a easy 2.4 GHz crystal radio with a resonant antenna, an impedance-matching community tuned to 2.45 GHz, and a two-stage voltage multiplier made with environment friendly Schottky diodes to transform RF alerts into usable DC energy. The antenna, a rigorously simulated and optimized meander antenna, achieves roughly +3.8 dBi achieve and maintains good return loss throughout the two.4 GHz band.
The sunshine-harvesting mechanism on the cardboard makes use of specifically chosen LEDs to seize ambient mild and convert it into usable electrical power. Whereas LEDs are primarily used to supply mild, they’ll additionally work backwards and performance as small photovoltaic cells when uncovered to mild. The harvested mild power generates a voltage, which is then directed to the power accumulation rail for rapid use, or saved in a supercapacitor for later consumption. The system is very environment friendly, able to working on as little as 200 lux of sunshine — in regards to the brightness of a dimly lit room. This uncommon design allowed the cardboard to reap power with out the majority of conventional photo voltaic panels.
One other attention-grabbing function of the cardboard is that it may be managed by way of a 2.4 GHz Wi-Fi community. This works by utilizing amplitude-shift keying to modulate the two.4 GHz Wi-Fi sign’s energy. A management net web page on a cellphone or pc streams or pauses information to a websocket connection, creating excessive (information despatched) or low (no information despatched) sign energy states. The cardboard detects these energy modifications with out becoming a member of the community and interprets them as binary 1s or 0s.
To decode instructions, the cardboard samples the RF sign and appears for a Barker-7 sequence for synchronization, adopted by a 16-bit payload containing one among eight legitimate instructions. The cardboard processes the payload, executes the corresponding motion, and confirms profitable decoding by flashing an LED. Vary is determined by energy: when powered by way of RF from a cellphone, the cardboard have to be close by, however with exterior energy (USB or supercapacitor), it really works over a couple of ft.
On the floor, this may increasingly appear to be a typical PCB Christmas tree construct, however on nearer inspection it rapidly turns into clear that this is not your grandma’s digital card. Take a look at the technical write-up of the challenge for all the main points, and if you wish to construct you personal, be certain to check out the directions as properly.This digital vacation card is powered by ambient power (📷: Jeff Keacher, Sean Beever)
The {hardware} parts (📷: Jeff Keacher, Sean Beever)Vitality will be harvested from leaking microwave emissions (📷: Jeff Keacher, Sean Beever)
