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
Robin singing, Soprano Pipistrelle echolocating and communicating with social calls
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Common Pipistrelle echolocating
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Soprano Pipistrelle echolocating and social calls
Serotine (or Noctule?) echolocating
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Myotis species bat (possibly Daubenton's) echolocating
Robin singing plus Noctule (or Serotine?) echolocating
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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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