Figure 3-7 illustrates how the internal peripherals of the CC13xx are utilized to design a simplified, ultra-low-power glass break detector with an external piezoelectric sensor. For this use-case we used the internal Comparator B together with a reference DAC and ADC. The COMPB peripheral is a low-power clocked comparator that is updated at 32kHz. COMPB can be used to continuously monitor slow signals and wake up the Sensor Controller from standby mode. Monitored signals include but is not limited to power supply voltages or analog sensor outputs. In Sensor Controller Studio, the threshold voltage of the COMPB peripheral can be configured using the internal reference DAC. Once the piezoelectric sensor signal surpasses the configured threshold, the system samples the entire piezo signal over a dedicated time using the internal ADC. This sampled data is then used to calculate the signal’s energy, allowing differentiation between a knock on the glass and an actual break.

Figure 3-7 High-Level Glass Break Detection Block Diagram

Figure 3-8 Internal Connection of Sensor Controller Peripherals

Figure 3-9 was generated by connecting a piezo sensor in the topology that is mentioned previously. By vibrating the board with the Sensor Controller + piezo, we can simply plot different voltage spikes that are reaching between 0.5V to 5V (depending on how large is the resistor you load the piezo sensor with). Then by analyzing the signals and the energy, we can understand what is considered as a break and was is considered as a normal knock or vibration.

Figure 3-9 Piezo Sensor Signals