Project Overview
"Qi-Logics" is a sophisticated power management sub-system designed for encapsulated embedded devices. Disassembling a compact enclosure for battery replacement is often impractical; thus, this project implements Near-Field Inductive Charging and Active SoC Diagnostics. By integrating a Qi-compliant receiver with a modified CC/CV charging controller, the module creates a "seamless" energy profile for any miniaturized Arduino project.
Technical Deep-Dive
- Inductive Energy Transfer (The Qi Standard):
- Faraday’s Law of Induction: The system utilizes a primary coil (transmitter) to generate a varying magnetic field, which induces an electromotive force (EMF) in the project’s secondary coil.
- Resonant Coupling: To maximize efficiency, the receiver circuit is tuned to the same resonant frequency as the transmitter, allowing power transfer across the non-conductive enclosure wall without physical copper contacts.
- Li-Ion Charging Forensics (TP4056 Modification):
- Constant Current (CC) Phase: The TP4056 IC is a linear charger. For a 250mAh battery, a standard 1A charge rate represents a dangerous 4C stress level.
- The $R_{prog}$ Calibration: To ensure battery longevity and safety, the SMD resistor on Pin 2 ($R_{prog}$) must be swapped. Changing the default 1.2k resistor to a higher value (e.g., 5k to 10k) reduces the charging current to ~130mA, aligning with the recommended 0.5C charging curve for small-form-factor lithium cells.
- High-Precision SoC Monitoring:
- Internal Bandgap Reference: Standard Arduino ADC readings fluctuate as the supply voltage drops. To solve this, the firmware utilizes the 1.1V Internal Reference. This stable silicon-based voltage remains constant even as the Li-Ion discharge curve falls from 4.2V to 3.0V.
- Static Current Drain: A high-impedance 680k/220k Voltage Divider is used to scale the 4.2V battery voltage down to the <1.1V domain. Using high-value resistors is critical for energy forensics, as it minimizes the parasitic current "leakage" through the measurement bridge.
Engineering & Implementation
- HMI Diagnostic Interface:
- The SSD1306 OLED provides visual feedback on the Battery Voltage ($V_{bat}$) and calculates the remaining percentage capacity. The UI includes dynamic icons that represent the three primary states: Discharging, Alert (<15%), and Charging.
- The Two-Way Switching Topology:
- To prevent interference between the measurement ADC and the high-voltage charging rail, a DPST switch isolates the battery. In "Run" mode, the battery drives the Pro Mini; in "Charge" mode, the rails are physically switched to the Qi-Receiver’s output.
- Thermal Consideration:
- Linear charging (TP4056) generates heat proportional to the voltage drop ($V_{in} - V_{bat}$). In a sealed case, this heat can be detrimental. The inductive coil itself also generates eddies. Future iterations may utilize thin copper foil as a heat spreader to protect the LiPo chemistry.
Conclusion
Qi-Logics provides the blueprint for "Forever Devices"—projects that never need to be plugged in. By mastering charge-rate calibration and stabilized analog sensing, developers can build robust, water-tight, and maintenance-free electronics.