In all of these hex-char converters, there is the problem of eye-strain trying to match up the 1 to 1 relationship between the chars and the hex values. (Let's see did I count over 10 chars or was that 11, etc). It's better to display the chars and hex values together, so you can see the match at a glance. Below is some code which does that. If you could do that with your tk script, it would be a great app.

#!/usr/bin/perl -wnl012
# Prints the contents of a file a line at a time 
# followed by the ASCII value of each character in vertical columns. 
# Useful for debugging. 
# If no filename is specified then input is read from the keyboard. 
# Version 1.00 Ian Howlett ian@ian-howlett.com 6 July 2001 
# Version 1.10 James Yolkowski ajy@sentex.net 8 July 2001 

print;                          # Print the line we've just read 
@hexvals = map {sprintf "%02X", ord $_} split //; # Get hex value of e
+ach char 
for $a (0, 1) {print map {substr $_, $a, 1} @hexvals} # Print the hex 
+values. 
#print "\n";
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Janitored by Arunbear - removed pre tags to improve readability