This README provides instructions and information about the battery monitoring system implemented in a DIY handheld device. The system utilizes the SPI interface for communicating battery status in real-time.

The system measures the voltage level of the battery connected to an analog pin on a microcontroller and sends this data over SPI to a host device. This setup is intended for use in low-power, real-time applications such as a handheld gaming device or portable instrument.

• Real-Time Battery Monitoring: Measures battery voltage in real-time and sends it via SPI.
• Interrupt-Driven Communication: Utilizes the SPI interrupt to handle data transmission seamlessly in the background.
• Simple and Efficient: Runs an empty loop in the main program while handling all data communication in the interrupt service routine, optimizing power consumption.

• Any compatible microcontroller with SPI support and an ADC (Analog to Digital Converter).
• Battery connected to an ADC capable pin (in this example, A2).

1. Configure the microcontroller:

   • Set up the SPI communication by configuring the MISO pin as output.
   • Enable SPI and SPI interrupt in the setup to allow asynchronous data handling.

2. Voltage Reading and Calibration:

   • Adjust the analogRead(batteryPin)-440)/2 formula based on your battery's voltage range and the reference voltage of your ADC for accurate readings.

1. Upload the provided code to your microcontroller using your preferred IDE (e.g., Arduino IDE).
2. Connect the battery to the specified analog pin (A2).
3. Connect the SPI lines (MISO, MOSI, SCK, SS) to your host device if necessary.

Once the setup is complete and the code is running:

• The microcontroller will automatically read the battery voltage and output it over SPI whenever a transmission is completed.
• The host device can continuously receive battery status without polling, reducing the processing overhead.

• The code does not include error handling or power-saving modes, which may be necessary for battery-operated devices.
• Calibration is crucial for accurate readings; ensure that the voltage divider and reference voltage are correctly set up for your specific battery and microcontroller.

This software is provided "as is", without warranty of any kind. Use at your own risk.