# 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="?"
n=0
logic="0"
# Use "H" for this DEMO although the commented out "LED" may look better.
LED="H"
# LED=unichr(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.
