AFC2 - Sensors for more efficient aquaculture

Purpose and goals

The project develops a wireless sensor system that will send sensor data in real time. The sensors measure parameters at individuals in the population but also describe external factors.

Challenge

The system needs to be very small but at the same time be able to communicate wirelessly underwater and be online for months. Batteries that meet the size requirements have a capacity of approximately 5 mAh, which sets the need for extremely low quiescent current. The power from the transmitter must be optimized and this puts high demands on the receiver side. The system operates under water and must therefore be waterproof.

Solution

The sensor system collects data using a microcontroller whose main feature is low power consumption. A real-time clock (RTC) has also been added to the system, which can shut down the system completely for a certain period of time. The current in idle mode is in the order of 10 nA. The transmitter element of the underwater communication is a piezoelectric tube whose mechanical resonant frequency is the same as the carrier frequency. The system wakes up measures sensor data from three sensors, the data is modulated on the carrier and transmitted to a hydrophone located on the edge of the pen. The wake-up / sleep time ratio in the current configuration is 0.4%.