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  • pipistrelle
Picture - About pipistrelle
π•pistrelle?
​INSTRUCTIONS
ASSEMBLY
FIRMWARE
RESOURCES
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π•pistrelle 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 contains
  • Knowles SPU0410LR5H-QB solid-state ultrasonic microphone
  • Microchip MCP622-E/SN dual op-amp with high gain-bandwidth
On-board 7.2kHz first-order high-pass filter for suppression of low frequencies and speech
  • Additional programmable 1.9kHz / 3.8kHz / 7.5kHz high-pass filter in firmware for more aggressive low frequency / speech suppression
Bandpass filter on audio output acts as low-pass filter for PWM audio output and as AC coupler
10-LED real-time spectrum and informational display
Two buttons, endless rotary encoder
microSD card interface for recording 384kHz wav files


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 
Speech synthesiser for frequency and bat ID feedback
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 RTTX (Real-Time Time eXpansion) modes
  • On-board RAM limits duration of RTTX 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 :
  • Onboard Real-Time Clock must be set by AudioMoth smartphone app to allow recording - download for iOS here and for Google Play here
  • Overnight mode triggered by triple-click of right button, acknowledged by a recognisable flash pattern
  • Device is in low-power mode during daylight hours
  1. ​​DAC is silenced
  2. Signal analysis is halted
  3. Spectrum LEDs go dark
  4. '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)

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 : Approx. £17.00 per unit 
'Recorder' configuration : Approx £12.50 per unit (recorder omits LEDs and audio output circuits)
'Synthesizer' configuration : Approx £20.00 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

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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
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Serotine (or Noctule?) echolocating
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Myotis species bat (possibly Daubenton's) echolocating
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Robin singing plus Noctule (or Serotine?) echolocating

​Two recordings of Lesser Horseshoes from a field trip to Portugal, May 2022 - this shows that π•pistrelle is comfortable capturing data above 100kHz
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Common Pipistrelle and Lesser Horseshoe, Portugal
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At least two Lesser Horseshoes, Portugal
Below are some files for you to download and review in Kaleidoscope.

21_03_51_soprano_pipistrelle-clipping.wav
File Size: 4194 kb
File Type: wav
Download File

21_06_15_Serotine_robin_singing.wav
File Size: 4194 kb
File Type: wav
Download File

22_07_56_common_pipistrelle.wav
File Size: 4194 kb
File Type: wav
Download File

22_33_15.wav - Common Pip and Lesser Horseshoe
File Size: 4194 kb
File Type: wav
Download File

22_42_52-sopranopip_quiet_serotine.wav
File Size: 4194 kb
File Type: wav
Download File

22_32_58.wav - Lesser Horseshoe
File Size: 4194 kb
File Type: wav
Download File

                                                                                        
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