Re: Filter/Speed/Meter & DON'T meter using a Nikon Camera

["R. C. Lacovara" <lacovara@xxxxxxxxxxx>]

At 01:47 PM 10/4/00, you wrote:
>bob ,
>find a heat absorbing glass inside of
>a slide projector and see what it blocks.
>Just curious, because it it pretty green.
>and does a good job of keeping a transparency from melting.

Hmm. Easy enough this weekend, I'll pull apart an old projector.


>BTW I bought some eg&g photo cells a couple of years ago
>and they all have green/blue glass filters over the sbc.

Without knowing what they were intended for, it's hard to know whether the 
coating was to block IR or merely protect the cell.


>And yes you are right about remotes pulsing brightly.
>I think that they charge a capacitor and discharge it for a short duration
>at a voltage over the led's rating. The pulse just happens to be too short
>to burn it out similar to the principle of an electronic flash?

Ah, they aren't operated like flash tubes. Flash tubes are connected to a 
source of high voltage on a capacitor. When it's time to flash, there's a 
second system to start the ionization in the flash tube, which then allows 
the capacitor to discharge through the tube. I'm not sure how variable 
intensity flash circuits work, since the discharge isn't to empty the 
capacitor, but is regulated by some other circuit.

LEDs in remotes are driven by integrated circuits at relatively low 
voltages, and don't depend on capacitive discharges. But the key you hold 
down determines the exact pulse pattern for the function the key 
represents. Basically, a particular short pattern is associated with each key.

The pattern is repeated over and over, as long as you hold the key. I 
suspect that we are seeing the repeated patterns, not the details of the 
pattern, as the LED is turned on and off. I doubt that the meters are fast 
enough to respond to the bit pattern within the control word, but the 
control word itself probably repeats slowly, perhaps 4 to 10 times per second.

Bob

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