# A Novel Plug-in Board for Remote Insect Monitoring
## 3 Results
### Power Consumption  
The computational load and the type of information transmission significantly influence the power consumption of an embedded system. Since the sensing device supports two communication units, the power consumption of the sensing device must be examined separately with both units. During the measurements, the input voltage was 7.3 V (voltage of the used battery), while the sampling frequency was 1 Hz. Moreover, the unused components, such as Bluetooth and activity LEDs, were deactivated. The outcome of the measurements can be seen in Figure 11. According to the measurements, the average power consumption was 2.4 W with LTE-based information transmission and 2.12 W with LoRa-based transmission in the active period. In the inactive period, it decreased to 22 mW. Similarly, the average current loads were 0.329 A and 0.290 A with LTE- and LoRa-based information transmission in the active state, respectively. In the inactive state, it was 0.003 A.  
Figure 11: Power consumption of the circuit with different communication modules. Figure 10: Sample image of cached insects taken by the sensing device (**left**) and the moths detected by the insect-counting algorithm (**right**). predict the operating time of the device. In the case of LTE communication, if we calculate with a 456 s active state period, the average current load per day is approximately 0.0047 A. Thus, the sensing device can run for about 1872 h (78 days) with our 11,000 mAh battery (80% efficiency). In the case of LoRa communication, the operating time is a little bit longer (80 days) because both the average active state (427 s) and the average current load (0.0046 A) are smaller than in the case of LTE communication. However, those operating times depend on several factors, such as ambient temperature, battery condition, age, etc. It is also important to highlight that changing the moth-counting algorithm can significantly change the operating time of the sensing device. Depending on the insect type, the earlier calculated operating time may not cover the whole insect swarm period. In this case, a solar charger circuit can fix the problem. Such a solar charger circuit is also placed on the plug-in board (Figure 13). The heart of the charger is an LT3652 power-tracking battery charger from the Linear Technology Corporation. It operates in a voltage range between 4.95 V and 32 V, and it provides an externally programmable charge current of up to 2 A. The LTE3652 can be adjusted to terminate charging when the charge current falls below a threshold level. After charging is terminated, it goes into standby mode. In standby mode, its current consumption is only 85 uA. The next charging cycle will start if the battery voltage falls 2.5% below the pre-defined float voltage. As another charging shutdown option, the charger contains a timer that can terminate charging after the desired time has elapsed. However, this option has not been used in our schematic. The output battery voltage can be programmed using a voltage divider via the V\({}_{\text{FB}}\) pin. The charge current can also be programmed via the SENSE pin with an appropriate resistor value. The circuit in Figure 13 has been designed for a 7.3 V battery that can be charged with the maximum 2 A current. If the sensed battery voltage is very low, the charger IC automatically enters a battery precondition mode. In this case, the charge current is reduced to 15% of the programmed maximum. Utilizing the solar charger circuit, we can fit the capacity and the solar panel's power according to the target insect's swarm period. To estimate the battery capacity and solar panel power, we need to know the expected average power consumption per day. With LTE information transmission, this value is 0.035 W.  
Figure 13: Solar power charger circuit.