HP-65 Morse Code

[Dan Lewis]

Awhile back, I was using my HP-35 to calculate the plate current in one of the vacuum tubes of an old radio I was repairing. I got a little too close to the radio's antenna with the calculator and I heard an awful squealing noise. It was then that I realized the LED display was acting as a crude (and even unintentional) AM radio transmitter. Then I decided to have some fun. I pressed the divide key with an empty stack, so the display would blink. Those "blips" on the radio got me thinking, "What if I could modulate that noise it's making, I COULD SEND A MESSAGE IN MORSE CODE!"

Well, with the HP-65 (or other programmable HP with LEDs), it's possible!

I decided that I was going to use the calculator's speed to my advantage. Since it takes very little time to execute a g NOP, I could place many of them in sequence. Just how many in a row would dictate what was being sent, Dah or Dit.

To break these Dahs or Dits apart, I figured out I could use the RCL instruction.

The first message I made was (of course) SOS, or ... - - - ... in CW. CW stands for "continuous wave" and is amateur radio speak for Morse code (which, actually, Samuel Morse had little to do with).

Anyway, the best I can come up with is below. RCL 1 just recalls 0 and acts as a break between the pulsing code characters. SST just skips over the g NOPs (after you have cleared the program memory).

LBL
A
f
SIN
RCL 1
SST x 4
RCL 1
SST x 4
RCL 1
SST x 4
RCL 1
SST x 12
RCL 1
SST x 12
RCL 1
SST x 12
RCL 1
SST x 4
RCL 1
SST x 4
RCL 1
SST x 4
GTO
A

The program uses 75 steps to repeat SOS in CW. When you press A (or B,C,D,or E), the program executes and you'll hear a very crude SOS over your AM radio around 730 kHz or so.

I tried to shorten the number of steps (resulting in faster send speed) so I could add my call sign. It worked, but it's too fast for a human to interpret, so it's useless.

Chances are someone would have to be pretty close to your calculator if they wanted to hear your distress call, so identification doesn't really help if they can't hear you anyway.

Maybe one of you can improve on this, I hope you enjoyed this little story.

-Dan

[Les Bell]

Quote:

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It was then that I realized the LED display was acting as a crude (and even unintentional) AM radio transmitter.

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Nice work! It reminds me of the first program I got working on my S-100 8080-based system, back in 1977, from an article by Steve Dompier in Dr. Dobbs Journal of Tiny Basic Computer Calisthenics and Orthodontia, or Running Light Without Overbyte, called "Music of a Sort".

I had a '65 back then, and was a radio amateur, too, but it never occurred to me to transmit CW with it!

Best,

--- Les

[http://www.lesbell.com.au]

[Mike Morrow]

Quote:

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The first message I made was (of course) SOS, or ... - - - ... in CW.

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I was concerned that what your program would generate was, according to your dot-dash representation above, the character string "S T T T S". The SOS distress signal would not be sent in such a manner. Nor would it be sent as "S O S", either, which is absolutely incorrect and the most common error seen in the movies and comic books, and among radio amateurs as well. It must be sent as one continuous signal, as ...---... with no character-to-character spacing between the S, O, and S.

But it appears that your program does send the signal correctly as one character. Congratulations!

Quote:

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CW stands for "continuous wave" and is amateur radio speak for Morse code.

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CW refers to the transmitter's emitted carrier signal which is should be of continuous constant amplitude and frequency while the key is depressed. The term CW contrasts to "damped wave" transmission...from the damped wave emissions generated each time early transmitters of the spark-gap era were keyed. The keying could be in any of a bazillion different "codes", including that which became international Morse. I cringe when I read "continuous wave" (the emission) as equivalent to "Morse Code" (the keying code). Clearly they are not the same thing at all.

Quote:

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(which, actually, Samuel Morse had little to do with).

---

He did pioneer the use of numbers-only messaging. Alfred Vail then expanded that to letters and special characters.

Many will be surprised that radiotelegraphy ceased commercially in its last sphere of world-wide use only in July, 1999, after treaty and rule changes allowed merchant vessels to sail without a radiotelegraph officer. I was licensed as such a commercial radiotelegrapher for a couple of decades.

[Garth Wilson]

I was very active on QRP CW as a radio amateur and got quite proficient at it, but quit being active in it when I got married in '84 and moved into an apartment that did not allow antennas. A couple of years later I got my 41cx and soon after got into synthetic programming and fooled around with Morse on that.

[LHH]

As a converse I've read that mainframe operators "back in the day" used an AM radio as a sort of monitor and could detect things like infinite loops and other processing anomalies by the sounds the radio picked up. Seems reasonable to me.

[Les Bell]

Quote:

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As a converse I've read that mainframe operators "back in the day" used an AM radio as a sort of monitor and could detect things like infinite loops and other processing anomalies by the sounds the radio picked up. Seems reasonable to me.

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They did. Another trick was to hook a speaker up to the carry flag of the main accumulator register and listen to the buzzing - back in the days when clock frequencies were measured in kHz.

Best,

--- Les

[http://www.lesbell.com.au]

[Harald]

Quote:

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Well, with the HP-65 (or other programmable HP with LEDs), it's possible!

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I suspect the HP65 is the only programmable HP that will work for this. On the classic calculators inductors are charged and then discharged into the LEDs. On later models the LEDs are simply driven from the Supply voltage with a resistor in series to the LEDs.

[Mike T.]

Not just the HP65, the Spice series make quite effective short range jamming devices as well.

Mike T.