MIKROE Qi RX Click is a compact add-on board made for the purpose of wireless power transfer. This board features the PIC16F15313, a general-purpose 8-bit MCU that makes a flexible, low-cost alternative to the wireless charging solutions based on ASICs from Microchip. It represents a simple, low-cost implementation of the Qi 1.1 5W wireless charging standard with the added functionality of a fully-featured Li-Ion charging controller. It can extend product life by reducing mechanical failures from connectors allowing the manufacture of devices truly resistant to water and dust. This Click board™ is suitable for wireless charging applications, cell phones, tablets, small hand-held devices, embedded electronics, and more.
NOTE: Qi RX Click needs to be placed near the suitable Qi Transmitter, also known as the charging pad, to successfully harvest the transmitted power.
Qi RX Click is based on the PIC16F15313, a general-purpose 8-bit MCU that makes a flexible, low-cost alternative to the wireless charging solutions based on ASICs from Microchip. The Qi RX Click allows users to quickly add wireless charging functionality to their projects without dealing with complex specific protocols or state machines. It is implemented using a general-purpose 8-bit MCU compatible with the Qi 1.1 (5W) standard that can be used in conjunction with any Qi 1.1 compatible wireless charging transmitters with the added functionality of a fully-featured Li-Ion charging controller.
Wireless charging uses the principle of magnetic induction to transfer power, which is similar to a conventional AC transformer where the receiver and the transmitter coils representing the transformer windings. The high-frequency signal of the Receiver Coil is rectified by a simple full-bridge rectifier implemented with four Schottky diodes (D1-D4), which output voltage is then monitored by the PIC16F15313 through a simple resistive divider R4 and R5. The communication with the base transmitter is implemented using Amplitude Shift Keying (ASK), as recommended by the Qi 1.1 standard, with two low-power MOSFETs (Q1 and Q2) and two capacitors (C4 and C5) used to modulate the absorbed power.
The rectified voltage is also applied at the input of the MCP1755, a low drop-out voltage regulator from Microchip, that supplies the 5V voltage for the battery charger and the PIC16F15313 up to 300mA. This LDO is associated with the charge LED indicator labeled as CHG that will indicate the charging progress and turns off once the battery charging is finished. The battery charging functionality is provided by the MCP73830, a single-cell Li-Ion/Li-Polymer battery charge management controller from Microchip.
The input current is measured by the PIC16F15313 using a shunt resistor R2 and the MCP6001, a single general-purpose OpAmp offering rail-to-rail input and output up to 6V from Microchip. The gain of this amplifier is set to 10. Measurement of the input current is necessary to accurately calculate input power and implement Foreign Object Detection (FOD) function using the power loss method.
Qi RX Click communicates with MCU using the MCP3221, a successive approximation A/D converter with a 12-bit resolution from Microchip. This device provides one single-ended input with very low-power consumption, a low maximum conversion current, and a Standby current of 250 μA and 1 μA. Data can be transferred at rates of up to 100 kbit/s in the Standard and 400 kbit/s in the Fast Mode. Also, maximum sample rates of 22.3 kSPS with the MCP3221 are possible in a Continuous-Conversion Mode with a clock rate of 400 kHz.
This Click board™ is designed to operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. It allows for both 3.3V and 5V capable MCUs to use the I2C communication lines properly. However, the Click board™ comes equipped with a library that contains easy to use functions and an example code which can be used, as a reference, for further development.
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