4 Software Architecture

This project has multiple functions. Each having a name describing its main purpose. There are two types of functions in this code: MCC-generated functions and custom application functions.

• app_PrepareEnvelope
• app_ChargingPulseGen
• app_ThrshldTimeMeas
• app_CheckEnvelopeThrsld
• app_ResetTimer
• app_ThrsldMeasDefaultValue

The SYSTEM_Initialize function is called at the beginning of the code and includes all the used peripherals initialization generated and configured using MCC. It configures the main clock of the project, the pin management, the CMP, the DAC, the FVR, the OPA, the CCP and the timers. Essentially, the project development used all the peripherals. Other functions generated by MCC for each peripheral will be used in the development.

The app_PrepareEnvelope function is the first application-related function and is used to prepare the LC sensor to detect the metal object. When the external capacitor is discharging while the PWM signal is generated, the external capacitor recharges. The PWM signal is generated by the app_ChargingPulseGen function that starts the Timer2 counter and waits until the Overflow Interrupt flag of Timer2 is set for a complete PWM cycle. It clears once the cycle has completed.

The app_ThrshldTimeMeas function generates the period that starts at the peak of the envelope and stops when the set threshold is reached. A delay of 1 ms is applied to prevent any false spike while charging the external capacitor and then while the function is running to measure the period of interest. Timer1 starts counting internally when the comparator output is logic-low, which means it’s at the peak of the envelope. The function above returns a 16-bit integer that represents the TMR1 counter value that is directly proportional to the measured period and stored in a local variable, measuredPeriod.

The on-board LED is used as a visual confirmation of metal detection. The period parameter's app_CheckEnvelopeThrshld function has it’s stored value compared with a previous set threshold if there are no objects in the LC sensor proximity. If the measured period is lower than the set threshold, the LED turns on and indicates the presence of a metal object. Otherwise, it will either turn off or stay off.

The app_ThrsldMeasDefaultValue function calibrates the threshold value for metal detecting. This function determines a default threshold period for a number of cycles set by the user to determine the average value of this threshold. This value can be affected by the difference between values of the external components so the average value of the threshold will be more precise. The LED will blink until the calibration is fulfilled. The first measurement value will be dismissed, and an error calibration factor deducted from the average determined value to avoid inaccuracies.

The app_ResetTimer function resets the TMR1 counter value and prepares the timer for a new measurement cycle.

All the above functions are called in a logical, continuous cycle repeated once every 100 ms and represented in the diagram below.