SPuC Bike Computer

The project is an open hardware initiative focused on developing a compact bicycle computer. This device excels in offering offline maps and real-time data through its motion sensors and GPS capabilities.

Key components of the device include:

• Processor and Memory: Equipped with an Allwinner T113-S3 processor and 128MB of RAM.
• Storage: Features 8GB of internal eMMC storage with microSD card support.
• Connectivity: Provides Wifi, Bluetooth, and LoRa connectivity.
• Display: Includes a 5-inch capacitive multitouch screen with 5 touch points.
• Sensors: Comprises an accelerometer, gyroscope, high-sensitivity magnetometer, and sensors for temperature, humidity, pressure, and light.
• Advanced Heart Rate and Oxygen Monitoring Sensor.
• Ports: Offers 2 USB Type-C ports and 1 USB Type-A port.
• Audio: Integrates stereo sound and a microphone.
• Power Management: Features comprehensive battery charge management and protection via a dedicated microcontroller, along with Soft Power ON/OFF.
• User Interface: Includes 3 quick-action buttons and a real-time clock with alarm functions.
• External Peripherals: It is capable of connecting to external sensors such as cadence and speed via Bluetooth Low Energy (BLE) or, alternatively, ANT+ through a USB device connected to any of the host ports.

The project aims to deliver a complete and customizable solution for cyclists by integrating advanced technology into a compact and efficient device.

Power Management

The primary power supply consists of a charging circuit based on the TP4056, complemented by a protection circuit utilizing the DW01A + FS8205A tandem. This configuration ensures the battery is safeguarded against overcharging and short circuits.

Thermal protection is provided by the R30 resistor, which shields the charging process from extreme temperature conditions. The voltage divider, formed by resistors R27 and R9, disables charging when temperatures fall below 0°C or exceed 45°C.

As detailed further, charging, discharging, and monitoring are managed by a dedicated microcontroller (ATTiny84), equipped with a voltage and current sensor (INA219). This setup allows for comprehensive battery monitoring and optimized charge/discharge management to extend battery lifespan.

The microcontroller assesses the charge and discharge status by monitoring the CHRG# and STDBY# pins of the TP4056 and can control the charging process via the CE pin. With data from the INA219, the microcontroller can halt charging at a specified percentage (e.g., 80%) or allow full charging as programmed by the main processor, even when the main processor is powered off.

A voltage converter is required to achieve the necessary 5V output, as the battery typically provides a voltage ranging from 3.2V to 4.2V. To accomplish this, a Powerboost circuit utilizing the FP6277 will be responsible for delivering the 5V output, regardless of the battery's charge state.

The pin in question is managed by the microcontroller to control the power supply to the circuit, either activating or deactivating it.

To maximize energy efficiency, when the device is connected to an additional power source, such as a USB Type-C charger or a power supply via the CON1 connector (for instance, wireless charging), a MOSFET-based circuit immediately switches the power source to preserve battery charge. If the external power supply is inadequate, the energy routing circuit will revert to using battery power.