Design Challenge

We set out to support Ontario bat conservation with a universal, non-invasive counter that works on existing bat boxes(rural or urban), handles high bat traffic and both small and large brown bats, and requires minimal cleaning. We didn’t want a special box or a lab setup — we wanted a drop-in device that meets all the criteria and outperforms competitors.

Proposed First Solution 

• We originally designed the system around a Raspberry Pi Zero 2W, using two PIR sensors, a load cell with amplifier, and an NFC module to detect and log bat activity.

• After comparing power consumption, we switched to a SAMD21 microcontroller, reducing draw from 0.2775 W to 0.0185 W and allowing us to run on a smaller 3.7 V battery while adding a microSD breakout board for data storage.

• The two PIR sensors were positioned inside and outside the bat box to detect motion direction, while the load celltracked weight changes to confirm entries and exits. A temperature sensor monitored internal conditions for context.

• Data was stored locally on the microSD and transferred via NFC (PN532) in .txt format when scanned—offering a quick, contactless way for maintenance teams to retrieve logs.

We had to make changes...

We replaced the load-cell concept with a sequential, beam-based counter to keep the system universal, ditched NFC for an HC-05 Bluetooth link (BLE), which gave smoother transfers, worked with a phone app for real-time pulls, and fit our power budget; we also switched to the Arduino MKR Zero to simplify data logging and keep consumption low. (We also enforce keeping BLE off except when retrieving logs to conserve battery.)

Our Solution

We built a self-contained system around an Arduino MKR Zero that logs to the onboard microSD, reads three IR break-beam sensors (two at the lower entrance, one at the top exit), and records temperature/humidity via DHT11 for context. Data can be retrieved by BLE using an HC-05 module or by pulling the SD card. The kit mounts to the side of any bat box in a waterproof enclosure and is serviced monthly for a quick battery swap. 

In lab validation, the sensor logic achieved ~96% entry/exit accuracy, data logging and BLE transfer worked reliably, and the enclosure passed drop and 24-hr waterproof tests.

Design Day