OS X (Apple)

Right guys...

The code below is a working example of the real DC voltage input with the output read off of a professional frequency counter. (The builtin counter inside AudioScope.sh works just as well but I needed to work out the calibration method so I tested the board on the bench at work. [ Shhhh, don't tell anyone... ;o) ]
The values of '$freq' were rounded up or down to the nearest 0 or 5...
The board has had one very minor modification, a 1M resistor added.
The code below is working a dream, thank you Don...
A highly mofified version will be incorporated into the main code over the WE...

Code:

#!/bin/bash
# lookup
freq=( 0 860 945 1025 1110 1190 1275 1355 1445 1520 1605 1685 1770 1855 1940 2025 2110 2200 4000 )
voltage=( 0.000 0.000 0.125 0.250 0.375 0.500 0.625 0.750 0.875 1.000 1.125 1.250 1.375 1.500 1.625 1.750 1.875 2.000 0.000 )
while true
do
	read -p "Simulate frequency from AudioScope builtin counter, 0 to 3999:- " num
	for ((i=0; i < ${#freq[@]}; i++))
	do
		[ "$num" -lt ${freq[i]} ] && break
	done
	[ $i -gt 0 ] && [ $i -lt ${#freq[@]} ] && V="${voltage[$i]}"
	echo "$V Volts DC..."
done