From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 25 Nov 2020 15:41:00 -0800
Subject: Re: [OT] Hyperikon Retrofit LED Tubes Without Ballast and
	fluorescent lamps and TV!
Thread-Topic: [OT] Hyperikon Retrofit LED Tubes Without Ballast and
	fluorescent lamps and TV!
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On the TV fluorescent lamps, yes the frequency was much higher than the
frame rate (though I don't remember what it was).

NTSC television is interesting! It's described at
http://mai.hallikainen.org/org/FCC/FccRules/2021/73/682/ . Prior to color,
the field rate was indeed 60 Hz, the power line frequency, to avoid
rolling "hum bars." With color, it appears everything is based on a
precise 5 MHz with the chroma subcarrier being 5 MHz * 68/88. The
horizontal scan rate is 2/455 * the chroma subcarrier frequency. The field
rate is then 2/525 * the horizontal scan frequency. I think that the
frequencies were chosen such that dots created by the chroma signal would
be white on one scan and black on the next, letting the eye cancel them
out. Similarly, the European PAL system switched the chroma phase 180
degrees on adjacent lines (since the image is interlaced, perhaps this
works out to just being a phase switch on each field). Chroma phase error
resulted in a hue shift, but in opposite directions on adjacent lines. So,
the eye averaged them out to avoid hue shift due to chroma phase drift.
Clever!

On light flicker, movie projectors used to use an incandescent "exciter"
lamp to light the sound track. Light would pass through the film to a
photocell. At first, the film density was varied to carry the audio, but
later the black to white area (width of a white or black stripe on the
film) was varied to carry the sound. Of course, if the lamp was powered by
60 Hz, you'd get 120 Hz hum in the sound. So, the obvious solution would
be to run the lamp on DC. But, many projectors instead ran the exciter
lamp on high frequency AC. There was a power oscillator to drive the
exciter lamp.

On the NE-2, one of my earliest project was an NE-2 based relaxation
oscillator running off a B battery. Choosing component values, I could get
a light flasher or get audio out of it.

Harold
http://w6iwi.org





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