Our project is a solar charger using a printed circuit board (PCB) coil for isolated, expandable charging. The PCB serves as a wireless charger, utilizing a 74hc14 chip as a tunable oscillator running at 800 kHz. The receiver boards have an adjustable voltage regulator to charge e-bike batteries. The goal of the project is to keep multiple e-bike batteries fully charged while parked at a bike rack, utilizing the power of the sun to sustainably charge the batteries. The use of a PCB coil allows for a compact and efficient design, while the tunable oscillator and adjustable voltage regulator ensure optimal charging capabilities. This solar charger is a sustainable and convenient solution for e-bike owners looking to keep their vehicles charged and ready for use at all times. In addition to its advanced charging capabilities, our solar charger is also designed to be beginner friendly. We have selected components that are readily available and easy to replace, ensuring that users can easily maintain and repair the charger if necessary. The through hole parts make them easy to solder, even for those who are new to electronics.

The transmitter in our solar charger design is based on a logic inverter, resistor, and capacitor, which form an oscillator that switches power to the coil at 800 kHz. A MOSFET acts as a switch to control the flow of power to the coil, generating an electromagnetic field for wireless power transfer. The oscillator frequency is determined by the values of the resistor and capacitor and can be fine-tuned using the potentiometer in the Schmidt trigger circuit. This allows for efficient and precise power transfer to the receiver

The receiver of our solar charger is designed to pick up the electromagnetic energy transmitted by the transmitter and use it to charge an ebike battery. To do this, the receiver uses a full bridge rectifier to convert the alternating current (AC) of the electromagnetic field into direct current (DC), which can be used to charge the battery. To ensure that the battery is charged to the optimal voltage level, the receiver also includes an adjustable voltage regulator. This component allows users to set the desired battery voltage level, ensuring that the battery is charged to a level that is safe and appropriate for the specific battery type and size.

update 12/31

The boards power up in the sun! I have it wired into the Ebike pack and I'll be able to get some test data on how much energy I harvest at my bike rack. If there's any traction, I'll fix the bugs in the board and unlock the gerbers of an improved V2.

V2 improvement list:

• Fixed component spacing for better fitment and easier solderability
• Anti-drain diodes on receiver output
• Pads breaking out coil connections to allow easy expansion of booster boards
• Using a socket with the trigger for easy repair, and better parts availability with a DIP Schmitt
• MOSFET driver for better performance, and wider parts availability (not as sensitive to Vth)

Ordering boards 11/29!

I tried to use easy to find parts like LM7805

Should be solderable by hand, even though it uses surface mounted parts

The BOM will include a can of tomatoes, a steel enclosure will boost coil efficiency

BOM costs are enough for 1 transmitter board, 3 receiver boards, and 1 set of extra parts (so maybe a 4th)