An Energy Autonomous Light Intensity Sensor for Monarch Butterfly Migration Tracking

This paper proposes a light intensity sensing circuit for a millimeter-scale system that tracks monarch butterfly migration. The system targets to be mounted on a butterfly and record light intensity during its 3-month migration. From the recorded data, light-based localization technique finds sunrise/sunset times and thus its longitude and latitude per day. The proposed circuit contributes to light measurement of the system by enabling battery recharging, averaging light level for 1-minute sleep mode, and suppressing temperature sensitivity. A prototype system achieves energy autonomy at >300lx. A prototype circuit obtains a 3σ inaccuracy of ±1.78% and σ/µ of 2.7% from 10lx to 100klx, a temperature sensitivity of 0.035%/°C from −20 to 85°C, and a supply sensitivity of 1.08%/V from 3.6 to 4.2V.