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..For STANDARD Python 2.6 and above...

This code will display a horizontal full colour analogue "VU" style meter. It displays green for normal, yellow for warning and red for danger with a critical error beep near the end of full scale, at value 120+.

This version is for Python 2.6 and above and only for the Linux, (*nix?), platform.

It is an "at a glance" display that is in colour rather than having to read say a digitally generated number.

A Python 3.x version can be found here:-

http://www.linuxformat.com/forums/viewtopic.php?t=13443

This has uses "for at a glance" voltmeters, ammeters, data-loggers, anemometers etc, etc...

Watch for wordwrapping etc...

NOTE:- This is Public Domain and you may do with it as you please.

73...

Bazza, G0LCU...

Team AMIGA...

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# SevenBitBargraph2x.py
#
# A DEMO 7 bit analogue bargraph generator in colour for STANDARD Python 2.6.x and Linux...
#
# (Original copyright, (C)2010, B.Walker, G0LCU.)
# A Python 3.x version can be found here:-
# http://www.linuxformat.com/forums/viewtopic.php?t=13443
#
# Saved as SevenBitBargraph2x.py wherever you like.
#
# This DEMO goes from safe green, to warning amber, to danger red, with a crirical
# error beep above 120 on the horizontal scale...
#
# Two system commands are required, "clear" and "setterm", for this to work.
# I assume that these are available on all recent and current Linux distros.
# The device /dev/audio is used so this must be free also. 
#
# It is useful for quick glance readings from say an 8 bit ADC used as a simple
# voltmeter, etc. Getting a digital readout is SO simple I left it out this time...
#
# To run use the following from inside a Python prompt...
# >>> exec(open("/full/path/to/code/SevenBitBargraph2x.py").read())
# OR...
# >>> execfile("/full/path/to/code/SevenBitBargraph2x.py").read()
# Tested on Debian 6.0.0 with Python 2.6.6.

# Add the required imports for this DEMO.
import os
import random
import time

def main():

	# For this DEMO set up variables as global...
	global column
	global count
	global bargraph
	
	column=0
	count=2
	bargraph="(C)2010, B.Walker, G0CLU. Now Public Domain"
	
	# Disable the cursor as it looks much nicer... ;o)
	os.system("setterm -cursor off")

	while 1:
		# Do a full, clean, clear screen and start looping.
		print os.system("clear"),unichr(13),"  ",unichr(13),

		# Set to terminal default colour(s).
		print "\033[0mSeven Bit Level Horizontal Analogue Bar Graph Display..."
		print
		print "Original copyright, (C)2010, B.Walker, G0LCU."
		print
		print "Issued to all as Public Domain."
		print
		print
		# Set the bargraph to light green for this DEMO.
		# This is equivalent to 0 for the column value.
		bargraph="        \033[1;32m|"

		# Generate a byte value as though grabbed from a serial, parallel or USB port.
		column=int(random.random()*256)
		# Now divide by 2 to simulate a 7 bit value.
		column=int(column/2)
		# Although this should never occur, don't allow any error.
		if column>=127: column=127
		if column<=0: column=0
		
		# Now to generate the bargraph...
		count=0
		while count<=column:
			# It is equivalent to BIOS character 222 for column value of 1 ONLY.
			if count==1: bargraph="        \033[1;32m"+unichr(0x2590)
			count=count+1
			if count>=2:
				while count<=column:
					# Change bargraph colour on the fly when entering the YELLOW zone... :)
					if count>=90: bargraph=bargraph+"\033[1;33m"
					# Change bargraph colour on the fly when entering the RED zone... :)
					if count>=100: bargraph=bargraph+"\033[1;31m"
					if count%2==0:
						# For every odd column value print this BIOS character 221.
						bargraph=bargraph+unichr(0x258c)
					if count%2==1:
						# For every even column value OVERWRITE the above with BIOS character 219.
						bargraph=bargraph+"\b"+unichr(0x2588)
					count=count+1
		# Print the "scale" in the default colour(s)...
		print "\033[0m        0   10   20   30   40   50   60   70   80   90   100  110  120"
		# Now print the meter and bargraph in colours of your choice... :)
		print "\033[1;32m        |    |    |    |    |    |    |    |    |    \033[1;33m|    \033[1;31m|    |    |"
		print "\033[1;32m        +++++++++++++++++++++++++++++++++++++++++++++\033[1;33m+++++\033[1;31m+++++++++++++++"
		print bargraph
		print "\033[1;32m        +++++++++++++++++++++++++++++++++++++++++++++\033[1;33m+++++\033[1;31m+++++++++++++++"
		print
		print "           \033[1;34m  Analogue resolution is half of one division, that is 1."
		print
		# Return back to the default colours and for this DEMO the column value...
		print "\033[0mColumn number",column,"\b...     "
		print
		print "Press Ctrl-C to stop..."

		# Do a critical error beep, [sine wave(ish)] for about 1second.
		if column>=120:
			# Set up the binary code as a crude sinewave.
			waveform=b"\x0f\x2d\x3f\x2d\x0f\x03\x00\x03"
			# Set audio timing to zero, "0".
			count=0
			# Open up the audio device to write to.
			# This could be /dev/dsp also...
			audio=open("/dev/audio", "wb")
			# A "count" value of 1 = 1mS, so 1000 = 1S.
			while count<=1000:
				# Send 8 bytes of data to the audio device 1000 times.
				# This is VERY close to 1KHz and almost sinewave.
				audio.write(waveform)
				count=count+1
			# Close the audio device access.
			audio.close()

		# Add a DEMO delay to simulate a simple digital voltmeter speed...
		if column<=119: time.sleep(1)
	
	# Enable the cursor again if it ever gets here... ;oO
	os.system("setterm -cursor on")
main()

# DEMO end.
# Enjoy finding simple solutions to often very difficult problems...

3 comments

John O'Hagan 10 years, 8 months ago  # | flag

How did you derive the bytes to write to /dev/audio to produce the (almost) sine wave? Generally, what is the principle of writing directly to /dev/audio to produce particular desired sounds?

Barry Walker (author) 10 years, 8 months ago  # | flag

Hi John O'Hagan...

Trial, error, and an viewing on an oscilloscope.

And it is a "crude" sinewave, not pure. With a simple passive filter it could be made into a nice example of a sinewave at 1KHz easily.

The sample rate is FIXED at 8KHz. Therefore 8 bytes fed to /dev/audio will give an accurate 1KHz signal.

There are two amplitude limits to generate any waveform, 0 and 63.

There is a non-linear ralationship between the output amplitude and any number between the above two limits. Careful manipulation of these numbers can generate various waveforms to white noise easily.

From this, (logarithmic), relationship, I found the values purely by trial and error and observation on an Oscilloscope as mentioned above.

As I experiment with HW I tried these values on various computers, and the result remained the same; a not-bad representation of a sinewave signal...

See here for other waveforms that can be generated...

http://code.activestate.com/recipes/577592-simple-1khz-audio-function-generator-using-standar/?in=user-4177147

Bazza, G0LCU...

Barry Walker (author) 10 years ago  # | flag

To the person(s) who voted this up...

You know who you are...

Many thanks from me...

Bazza, G0LCU...