Another Python Freebie, DC_IN.py...

Bazza — Sun Dec 04, 2011 3:01 pm

Author: Bazza

Posted: Sun Dec 04, 2011 3:01 pm

Hi all...

I recently uploaded this to <http://code.activestate.com/> and thought I
would share it with you lot... Another bit of my lateral thinking and has
opened up new avenues for experiment like a text mode Python Audio
I/O Modem using the audio socket(s) on my netbook, notebook and
laptop, a la Sinclair Spectrum Load/Save modem... ;o)

Watch for word wrapping etc...

Code:

# DC_IN.py
#
# This DEMO shows how to get DC, (Direct Current), into a computer without
# the need for Integrated Cirduits, USB, Serial, Parallel etc, etc...
# It is used in this code as a very simple Logic Probe that will give some
# indication of a Logic 0, 1 or indeterminate. Only the external microphone input
# is required. "/dev/dsp" IS required so install "oss-compat" from your distro's
# repository if you do not have "/dev/dsp"...
# Ensure the sound system is not in use, and, use the OS's mixing facilities to
# set any input and output levels...
# Tested on Debian 6.0.0 using Python 3.1.3 and PCLinuxOS 2009 using Python 3.2.2.
# (C)2010, B.Walker, G0LCU. Now issued as Public Domain.
# Written in such a way that anyone can understand how it works.
#
# A very simple VCO, (Voltage COntrolled Oscillator), can be found here...
#
# http://www.4qdtec.com/mvbz/vco2.gif
#
# Assume a supply rail of 5 Volts to the VCO along with the circuit of the probe below...
#
# +5 Volt rail on VCO, (Vcc).
# O-------------------------+
# |
# | +
# --+--
# D2. / \
# +---+
# |
# 1-4 Volt VCO I/P, (Vc). |
# O--------o---/\/\/\---o---o---/\/\/\---0 Probe I/P.
# | R2. | R3.
# O < | +
# | > --+--
# | R1. < / \ D1.
# | > +---+
# | < |
# | | |
# +--------o------------o-------o--------O -VE.
# 0 Volts. |
# ---+--- GND.
# Parts List. ///////
# -----------
# R1 = 1 MegOhm.
# R2, R3 = 470 Ohms.
# D1, D2 = 1N4148 Diodes.
# All tolerances are wide open.
# Sundries, stripboard, wire, etc...

def main():
# Make variables global; my choice... ;o)
global record
global n
global freq
global logic
global LED
global colour
# Set the startup values...
freq=0
record=b"?"
n=0
logic="0"
# Use "H" for this DEMO although the commented out "LED" may look better.
LED="H"
# LED=chr(0x2588)
colour="\033[1;32m"
while 1:
   # Do a 1 second recorded burst...
   audio=open('/dev/dsp', 'rb')
   # "record" is the "binary string" to be counted...
   record=audio.read(8000)
   audio.close()
   # Enter another loop to do the count...
   n=0
   freq=0
   while 1:
      # A VCO with a mark to space ratio of 1 to 1 will be used for this DEMO,
      # so "wait" until a "space" is found.
      # (For those that don't know.)
      #
      # +------+ +---
      # Square wave:- | Mark |Space |
      # ---+ +------+
      #
      # This ensures that the loop cycles when NO input is
      # applied to the microphone socket.
      # Exit this loop when "mark" is found or n>=8000...
      while record[n]<=127:
         n=n+1
         # Ensure as soon as n>=8000 occurs it drops out of the loop.
         if n>=8000: break
      # Ensure as soon as n>=8000 occurs it drops completely out of this loop.
      if n>=8000: break
      # Now the "mark" can loop until a "space" is found again and the whole
      # can cycle until n>=8000...
      while record[n]>=128:
         n=n+1
         # Ensure as soon as n>=8000 occurs it drops out of the loop.
         if n>=8000: break
      # Ensure as soon as n>=8000 occurs it drops completely out of this loop.
      if n>=8000: break
      # "freq" will become the frequency of a symmetrical waveform
      # when the above loops are finally exited, n>=8000...
      # Tick up the freq(uency) per "mark to space" cycle.
      freq=freq+1
      # Just 3 levels are displayed here but with more "if" statements much more
      # accuracy and range is easily possible. Also "look up tables" could be used if desired...
      # Set colour to Green for Logic 0, Red for Logic 1 and Yellow for indeterminate.
      # Logic 1 is approximately greater than 4 Volts.
      if freq>=3000:
         logic="1"
         # Red...
         colour="\033[1;31m"
      # Logic 0 is approximately less than 1 Volt.
      if freq<=300:
         logic="0"
         # Green...
         colour="\033[1;32m"
      # Indeterminate is between 1 and 4 Volts and/or a slow oscillation being measured...
      if freq>=301 and freq<=2999:
         logic="indeterminate"
         # Yellow...
         colour="\033[1;33m"
   # An ultra simple clear screen line...
   # This line is not needed for the demo but added for fullness...
   print("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n")
   # Now display the value in the same place on screen every time.
   # This assumes a 24 or 25 line Python Shell window. Just modify to
   # suit your particular Shell that you use...
   print("\033[0m\nSimple DC Input in the guise of a TTL level Logic Probe.\n")
   print("(C)2010-2011, B.Walker, G0LCU. Issued as Public Domain.\n\n\n")
   # Print a large coloured square "LED" for quick and easy viewing.
   for n in range (0,3,1):
      print(" "+colour+LED+LED+LED+LED+LED+LED)
   print("\033[0m\n\n\nLogic level is "+colour+logic+"\033[0m...\n\n\n\n\n\n\n\n\n")
main()
# End of DC_IN.py DEMO.
# Enjoy finding simple solutions to often very difficult problems.

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Another Python Freebie, DC_IN.py...