90 lines
3.1 KiB
Python
90 lines
3.1 KiB
Python
#!/usr/bin/python
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# Bicycle Bell/Horn firmware
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# Copyright (C) 2015 Stuart Longland
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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import math
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import wave
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import struct
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import textwrap
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# Generate a horn sound
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F_sample = 6400 # 6.4kHz sample rate
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# Horn frequencies and amplitudes
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A_horn = 0.8
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FA_horn = [
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(485, 10**(-20.4/20)),
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(618, 10**(-15.4/20)),
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(762, 10**(-7.3/20)),
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(967, 10**(-13.4/20)),
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(1147, 10**(-15.0/20)),
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]
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T_attack = 0.029 # Rise time, seconds
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T_hold = 1.000 # Hold time, seconds
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T_decay = 0.300 # Decay time, seconds
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N_samples = int(math.ceil((T_attack+T_hold+T_decay) * F_sample))
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T_hold_end = T_attack + T_hold
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duration = T_hold_end + T_decay
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def amplitude(t):
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if t < T_attack:
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return (1.0 + math.sin((t*math.pi)/(2*T_attack)))/2.0
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elif t < T_hold_end:
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return 1.0
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else:
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t -= T_hold_end
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return (1.0 + math.cos((math.pi*t)/T_decay))/2.0
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horn = lambda t : amplitude(t) * sum([ \
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a * A_horn * math.sin(2*math.pi*f*t)\
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for f, a in FA_horn \
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])
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samples = []
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for n in range(0, int(duration*F_sample)):
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t = float(n)/float(F_sample)
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samples.append(int(127*horn(t)) + 127)
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assert samples[-1] >= 0, '%s <= 0' % samples[-1]
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assert samples[-1] <= 255, '%s > 255' % samples[-1]
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num_samples = len(samples)
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# C output
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with file('hornsnd.c','w') as f:
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f.write('#include "hornsnd.h"\n')
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f.write('const uint8_t horn[%s] PROGMEM = {\n' % num_samples)
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f.write('\n'.join(textwrap.wrap(', '.join([str(s) for s in samples]),
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initial_indent='\t', subsequent_indent='\t',
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expand_tabs=False)))
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f.write('\n};\n')
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with file('hornsnd.h','w') as f:
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f.write('#include <stdint.h>\n')
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f.write('#include <avr/pgmspace.h>\n')
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f.write('#define HORN_RATE (%s)\n' % F_sample)
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f.write('#define HORN_LOOP_OFFSET (%s)\n' % int(T_attack*F_sample))
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f.write('#define HORN_LOOP_SZ (%s)\n' % int(T_hold_end*F_sample))
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f.write('#define HORN_SZ (%s)\n' % num_samples)
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f.write('const uint8_t horn[%s] PROGMEM;\n' % num_samples)
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# For the sake of analysis, we'll dump wav audio too
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f = wave.open('hornsnd.wav','w')
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f.setnchannels(1)
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f.setsampwidth(1)
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f.setframerate(F_sample)
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f.setnframes(num_samples)
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f.setcomptype('NONE','not compressed')
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f.writeframes(''.join([
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struct.pack('B', s) for s in samples
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]))
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f.close()
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