Raspberry Pi Bat Call Recorder

Transcription

1 Raspberry Pi Bat Call Recorder This project uses a Raspberry Pi and Wolfson Audio Card, with a simple LED and Push Button wired to the GPIO. A home-made ultrasound microphone is plugged into the headphone socket of the Wolfson card. Using a Bat Scanner, when bat calls are detected recording is started by pressing the button. The LED indicates that recording is active. Sound is captured at a sample rate of Hz until the button is pushed again. Holding the button down when stopping the recording causes the Pi to shut down safely. Attaching the push-button to the GPIO The Wolfson Audio Card appears to use all the GPIO pins, but two GPIO pins (#8 and #10) are available on the Wolfson card. Using these, plus the 3.3V pin and Ground as shown, it is possible to connect the push-button and LED. 3.3V 5V Ground Pin 10 Pin 8 Note that these connectors are 2mm pitch. Do not connect anything to the 5V pin! Pin 10 will be used for the push-button, and pin 8 for the LED. Wiring diagrams for each of these are shown below. Connecting things to the GPIO is done entirely at your own risk! Please check that you are happy with my wiring diagrams and check your wiring before powering on your Pi. For more information about connecting things to the Raspberry PI GPIO, visit Push Button LED 3.3V PIN 8 (GPIO 14) PUSH BUTTON PIN 10 (GPIO 15) LED GND 10kΩ 1kΩ GND 330Ω

2 Setting up GPIO Pins To set the GPIO pins on the Wolfson Audio Card for Input/Output on start-up of your Pi, add the following to /etc/rc.local, before exit 0: ($ sudo nano /etc/rc.local) # setup GPIO # enabling pin 15 as input: # exports GPIO pin 15 for use, sets the direction to "in" echo "15" >/sys/class/gpio/export echo "in" >/sys/class/gpio/gpio15/direction ### # set to active low if required (invert the value) # echo 1 >/sys/class/gpio/gpio15/active_low # input value can be checked by command below # cat /sys/class/gpio/gpio15/value ### # enabling pin 14 as output: # export GPIO pin 14 for use, sets the direction to output echo "14" >/sys/class/gpio/export echo "out" >/sys/class/gpio/gpio14/direction Making the Microphone To make a microphone capable of recording ultrasound, you can use an electret type microphone. Choose one with a good frequency response. The data sheet for the one I use specifies a range of 20Hz to 20kHz. For bat recording, a range of up to 100kHz or more may be required. The electret microphone should be able to record up to this frequency, but the sensitivity will be reduced. I haven t found this to be a problem (up to 96kHz - more on this later). A four pole 3.5mm Jack plug is also required ( Solder screened wire (e.g. Maplin XR20W) to the jack plug and electret as shown below. Tip: after tinning the wires, bend the ends 90 before soldering on to the back of the electrec microphone. After soldering, use heatshrink over the electret and wire to finish the microphone. MIC GROUND (SHIELD) Python script The python script for recording using the push button is on the following pages. You may need to copy the following two Wolfson files into /home/pi, or modify the code to point to the files: Record_from_Headset.sh Reset_paths.sh Save the folowing script as record.py in /home/pi.

3 # record.py # python code to record sound at press of button and light LED # push button again to stop # keep button held down when stopping recording to safely shut down the Pi # # # import RPi.GPIO as GPIO GPIO.setmode(GPIO.BCM) import time import os import subprocess import datetime import psutil #used to kill arecord #to install psutil: #sudo apt-get install python-dev #sudo apt-get install python-psutil procname = 'arecord' print "Resetting..." #reset playback paths for wolfson card subprocess.call ("/home/pi/reset_paths.sh", shell=true) # use pin 8 for LED # use pin 10 for button GPIO.setwarnings(False) GPIO.setup(14, GPIO.OUT) #8 GPIO.setup(15, GPIO.IN) #10 shut_down = 0 LED = 0 killed = 0 # check to see if there is a USB stick partitionsfile = open("/proc/partitions") lines = partitionsfile.readlines()[2:]#skips the header lines for line in lines: words = [x.strip() for x in line.split()] minornumber = int(words[1]) devicename = words[3] if minornumber % 16 == 0: path = "/sys/class/block/" + devicename if os.path.islink(path): if os.path.realpath(path).find("/usb") > 0: print "/dev/%s" % devicename USB = 1 # usb fitted, so can write to /media/usbstick, otherwise write to /home/pi filepath = " /media/usbstick" filepath = " /home/pi" subprocess.call ("/home/pi/record_from_headset.sh", shell=true) #set up to record from headphone mic print filepath try: while True: if GPIO.input(15) and recording == 0 and shut_down == 0: GPIO.output(14, True) #turn on LED to show recording recording = 1 killed = 0 timestamp = datetime.datetime.now().strftime('%y%m%d%h%m%s')

4 process = subprocess.popen ("arecord -Dhw:0 -r c 2 -f S32_LE -d0 " + filepath + "/record_" + timestamp + ".wav", shell=true) #channels = 2 for stereo print "PID " + str(process.pid) print "Recording started" # not recording # flash LED to show system is active if LED == 0 and recording == 0 and shut_down == 0: time.sleep(0.25) LED = 1 if LED ==1 and recording == 0 and shut_down ==0: GPIO.output(14, True) time.sleep(0.25) LED = 0 if GPIO.input(15) and recording == 1 and shut_down ==0: #button held during recording stops recording print "Recording stopped" for proc in psutil.process_iter(): if proc.name == procname: proc.kill() killed = 1 if GPIO.input(15) and killed == 1 and recording ==0: print "Shutting down..." shut_down = 1 subprocess.call(['shutdown -h now "System halted by GPIO action" &'], shell=true) time.sleep(0.1) except KeyboardInterrupt: print " Quit" # Reset GPIO settings GPIO.cleanup() Mounting a USB stick Use the following guide to mount a USB stick to your Pi, if that is where you want to record wav files to: The Python script above checks whether a USB stick is mounted at /media/usbstick and will use that. Otherwise, wav files will be saved in /home/pi. Using the Pi Bat Recorder Check your wiring, then check it again. Make sure that the microphone jack is fully pushed into the socket on the Wolfson Audio Card. Power on your Pi. The LED will probably glow/flicker as the Pi is booting. $ sudo python /home/pi/record.py will run the record script. The LED should be flashing slowly. Press the push button to start recording. The LED should be on continuously. Push the button again to stop recording.

5 Analysis of wav files Using Audacity, open a recorded wav file. Choose Tracks Stereo Track to Mono to convert the track to mono. The wav files are not recorded in mono due to a current limitation with the Wolfson Audio Card when recording at Hz. This rate is used as it allows analysis of sounds up to half this frequency Hz - which is what we need for most bats :-) Click the small arrow here, and select Spectrogram. You should be able to see a nice spectrogram of your bat calls. You may need to zoom in a bit. Spectrogram settings can be changed using Edit Preferences. What next? To get your script to run when the Pi boots, add sudo python /home/pi/record.py to /etc/rc.local, just before exit 0. August 2014