
π•pistrelle : an ultra-inexpensive, multi-function, ultrasonic handheld
field device for citizen bat science
Features :
Hardware features :
Processing by Raspberry Pi Pico - a low-power, high-performance, dual-core microcontroller
Powered by 3x AA cells or 5V USB powerbank
BatSignal ultrasound module features
10-LED real-time spectrum and informational display
Two buttons and endless rotary encoder
Micro SD card interface for recording
Bat Detector mode :
'Eyes to the skies' operation
Connect headphones or powered speaker to 3.5mm jack
Manual override and fine-tuning of heterodyne frequency via rotary controller ('classic bat detector' mode)
Switch between Heterodyne and RTX (Real-Time eXpansion) modes
Bat Recorder mode :
Overnight / multi-night unattended field recording :
On-demand recordings when in detector mode :
Recording requires "AudioMoth" iPhone / iPad / Mac / Android app
Bat Synthesizer mode :
For educational use, volunteer training or detector / recorder testing
Simply connect a low-cost L010 ultrasound speaker to headphone output
Reproduces synthesized echolocation calls of multiple UK bat species
Programmed species to include :
Currently selected species indicated on LED display
Build cost for 10-off units (early 2022 - global semiconductor shortage makes these costs somewhat volatile) :
'Detector' configuration : Under £19.00 per unit
'Recorder' configuration : Under £22.00 per unit (recorder includes Adafruit SPI SD breakout plus SD card)
'Synthesizer' configuration : Under £25.00 per unit (synthesizer requires L010 ultrasonic speaker and minor change to audio output filter)
field device for citizen bat science
Features :
- Frequency-scanning heterodyne / real-time time-expansion Bat Detector
- Full-spectrum 384kHz / 16-bit Bat Recorder
- Bat echolocation call Synthesizer
Hardware features :
Processing by Raspberry Pi Pico - a low-power, high-performance, dual-core microcontroller
Powered by 3x AA cells or 5V USB powerbank
BatSignal ultrasound module features
- Knowles SPU0410LR5H-QB solid-state ultrasonic microphone
- Dual op-amp with high gain-bandwidth
- Additional programmable 1.9kHz / 3.8kHz / 7.5kHz high-pass filter in firmware for more aggressive low frequency / speech suppression
10-LED real-time spectrum and informational display
Two buttons and endless rotary encoder
Micro SD card interface for recording
Bat Detector mode :
'Eyes to the skies' operation
- largely non-visual user interface
- auto-frequency scanning, audio feedback on bat frequency detection
- allows user to track and ID bats visually
Connect headphones or powered speaker to 3.5mm jack
Manual override and fine-tuning of heterodyne frequency via rotary controller ('classic bat detector' mode)
Switch between Heterodyne and RTX (Real-Time eXpansion) modes
- On-board RAM limits duration of RTX mode
- Most recent 170ms of sampled sound is played back, slowed down by a large factor
- Time Expansion factor preset to 16x - exactly 4 octaves lower than actual bat call
- If preferred this factor may be configured to 10x or 20x via configuration tool which patches firmware (requires a reflash of device)
Bat Recorder mode :
Overnight / multi-night unattended field recording :
- Overnight mode triggered by triple-click of right button, acknowledged by a recognisable flash pattern
- Device is in low-power mode during daylight hours
- DAC is silenced
- Signal analysis is halted
- Spectrum LEDs go dark
- 'Heartbeart' flash pattern on single Pico LED indicates sleep mode
- 'Wake on Bat' - during non-daylight hours, 5 second / 4MByte recordings to micro SD triggered by ultrasonic signal detection
- 3 fresh 2000mAh - 2400mAh rechargeables typically last for 2 overnight sessions
- Battery life highly dependent on bat activity - writing to SD card is power-hungry
- Storage capacity limited by SD card size
- 8GB-16GB typically good for 2 nights' recording, may need 32 or 64GB if the night is particularly busy
On-demand recordings when in detector mode :
- On-demand single recording of 5 seconds (single click of right button)
- Or 1 minute via 12 consecutive recordings of 5 seconds each (double click of right button)
Recording requires "AudioMoth" iPhone / iPad / Mac / Android app
- Sets Real-Time Clock for wav file timestamping and sleep management
Bat Synthesizer mode :
For educational use, volunteer training or detector / recorder testing
Simply connect a low-cost L010 ultrasound speaker to headphone output
Reproduces synthesized echolocation calls of multiple UK bat species
Programmed species to include :
- Noctule
- Serotine
- UK Pipistrelles (Common, Nathusius' and Soprano)
- Daubenton's
- Brown Long-Eared
- Greater Horseshoe
Currently selected species indicated on LED display
Build cost for 10-off units (early 2022 - global semiconductor shortage makes these costs somewhat volatile) :
'Detector' configuration : Under £19.00 per unit
'Recorder' configuration : Under £22.00 per unit (recorder includes Adafruit SPI SD breakout plus SD card)
'Synthesizer' configuration : Under £25.00 per unit (synthesizer requires L010 ultrasonic speaker and minor change to audio output filter)
HOW π•pistrelle WORKS
EXAMPLE RECORDINGS
4 or 5 species, captured in a 2 hour session in a rural garden in Wiltshire, April 2022
Recordings visualised and analysed using Kaleidoscope Free, from Wildlife Acoustics
Below are some example files for you to download and review in Kaleidoscope. These were recorded in a rural garden in Wiltshire, between 9.00pm and 11 p.m on 10th May 2022
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