🚀 go-pugleaf

        I have a circuit using one semiconductor chip and costing about 5$ that
can turn your Apple II, II+ IIe into a frequency meter.  I can additionally
send you a print out of the program or send me a blank 5 1/4" floppy, and
I'll send you the program on disk.  (Hey--send postage for the return :-))

        Oops, forgot a component make that about 7$.  We use the Apple power
supply and solder it right into the Apple.  We use a speaker for the micro
phone.

        It works well from < 100 Hz (depending on the size of the speaker) to
a little over 500 Hz.  This range works well for blowing notes in soft drink
bottles.

        I provide student teams with a soft drink bottle labelled with n Hz.
They are to add water (or remove water) as necessary to hit the n Hz frequency
+/- x% tolerance (I use 10%).  This gets them to see in a rudimentary way that
one of the determiners of frequency in a closed end vibrating air column is
the length.

        Student lips never touch the bottles.  We use a rolled quarter sheet
of paper (around a pencil is super) taped to stay in a tube.  Then we flatten
one end of the tube.  Placing the flattened end of the tube on the lip of the
bottle and holding the tube perpendicular to the axis of the bottle while
blowing provides a clear clean tone.

        We hold the speaker (microphone) to the side so the air stream from
the tube will not interfere with the correct reading.

        Use snail mail with SASE for the diagram alone, or the diagram with
software, or whatever you need.  I haven't written a lesson plan, but you
should be able to work up your own in the form of a challenge.  We find that
6 computers is more than adequate for 30 - 35 kids.

Charles Toth
Owens Science Center
9601 Greenbelt Road
Lanham, MD   20706

PS Give me a week or two to respond.