Quick and dirty Hellschreiber code for ToorCon San Diego 15's software defined radio workshop

SDR Hellschreiber

#!/usr/bin/env python

import math

import numpy

import scipy.fftpack
import scipy.signal

letters = {
	' ': [
		"     ",
		"     ",
		"     ",
		"     ",
		"     ",
	],
	'/': [
		"*    ",
		" *   ",
		"  *  ",
		"   * ",
		"    *",
	],
	'C': [
		"*****",
		"*    ",
		"*    ",
		"*    ",
		"*****",
	],
	'E': [
		"*****",
		"*    ",
		"***  ",
		"*    ",
		"*****",
	],
	'L': [
		"*    ",
		"*    ",
		"*    ",
		"*    ",
		"*****",
	],
	'M': [
		"*****",
		"* * *",
		"* * *",
		"* * *",
		"* * *",
	],
	'N': [
		"*****",
		"*   *",
		"*   *",
		"*   *",
		"*   *",
	],
	'O': [
		"*****",
		"*   *",
		"*   *",
		"*   *",
		"*****",
	],
	'R': [
		"*****",
		"*   *",
		"*****",
		"*  * ",
		"*   *",
	],
	'T': [
		"*****",
		"  *  ",
		"  *  ",
		"  *  ",
		"  *  ",
	],
	'W': [
		"*   *",
		"*   *",
		"* * *",
		"* * *",
		"*****"
	],
}

message = "/// WELCOME TO TOORCON "

image = []
for c in message:
	image.extend(letters[c])
	image.append("     ")

sampling_rate = 1e6

line_rate = 5
samples_per_line = sampling_rate / line_rate
samples_per_line = 1 << int(math.ceil(math.log(samples_per_line, 2)))
fft_width = samples_per_line
print('samples per line: %d' % samples_per_line)

char_width = 5
print(fft_width)

waveform_window = scipy.signal.blackman(fft_width)

bin_per_hz = float(fft_width) / sampling_rate

pixel_stride = int(5e3 * bin_per_hz)
pixel_width = 1

#bin_offset = int(100e3 * bin_per_hz)
bin_offset = 0
print('offset: %d' % bin_offset)
print('stride: %d' % pixel_stride)

waveforms = []
for line in image:
	spectrum = numpy.zeros((fft_width,), dtype=numpy.complex64)
	for n in range(len(line)):
		pixel = 0 if line[n] == ' ' else 1
		bin_start = bin_offset + n * pixel_stride
		bin_end = bin_start + pixel_width
		spectrum[bin_start:bin_end] = pixel
	#spectrum = scipy.fftpack.ifftshift(spectrum)
	waveform = scipy.fftpack.ifft(spectrum)
	#waveform = scipy.fftpack.fftshift(waveform)
	waveform *= (fft_width / char_width)
	#waveform *= waveform_window
	waveforms.append(waveform)

waveforms = numpy.concatenate(waveforms)
waveforms.tofile('banner_bb.c64')