Listening to your LED Flashlight

I was walking the dog this evening and was carrying a small AM/FM radio (Tuned to an AM station) and also a McL4 with a clickie. I noticed something a bit unique: If the light was turned on close to the radio, it would apparently couple to the radio and then an amplified, variable pitch sound would eminate from the radio. It was akin to the whirring, SW Radio interferance sound which raised in pitch and then dropped again. Everytime I turned off the light it stopped.

Anyone ever notice anything like this? /ubbthreads/images/graemlins/confused.gif

yes my direct drive led lights
are the loudest

We used to use the original Texas Instruments TI-30 calculator to test the built in window antenna in cars. The modulator circut oscillator leaked RF like crazy in a low enough of a field to isolate a break in the antenna wire. Probably in a light you would get more signal by pointing the beam at the antenna as the body shell might absorb some of the field.

I think the effect leads to the acceleration of Arthritis or chronic hangnails in your torch hand. I read that on the internet somewhere so it must be true. /ubbthreads/images/graemlins/nana.gif

I thought DD used no active circuitry. Are the LEDs, themselves, creating RFI? Am I a little (a lot?) slow and didn't understand you were teasing? /ubbthreads/images/graemlins/grin.gif

yes I was joking

some times I can not stop my self

never grow up never grow old

You can also record the ARC4 noise and turn it into an art form:

kool I think I have seen those screens before

Any of the regulated flashlights will generate some RFI. There are also many other household items that have a clock oscillator inside that produces RFI. Place a calculator next to an AM radio, tune to a blank spot on the dial, then push a few buttons on the calculator and listen; ou can "hear" it thinking. The functions that require more processing time will produce more interesting sounds as the calculator swaps information in and out of it's registers.

[ QUOTE ]
markdi said:
yes my direct drive led lights
are the loudest

[/ QUOTE ]

Hmmmm, DD lights should not produce any RFI. They are being driven off the batteries either directly or through a dropping resistor and thus have no "switching" currents. Regulated lights typically use switching DC-DC converters and these should produce some interference depending on the switching frequency.

CM

CM,

[ QUOTE ]
markdi said:
yes I was joking

some times I can not stop my self

never grow up never grow old

[/ QUOTE ]

/ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/grin.gif

Newbie-Now I see what I've heard. Cool /ubbthreads/images/graemlins/thumbsup.gif

Oh-so it is switching RFI.

Thanks to all the sparkies who answered...

Any flashlight that uses a driver circuit (other than just one or more resistors) can produce RFI.
Some of them also produce a faint but audible sound, such as the Super Baby Pin and the SureFire L2.

So at the next CPF gathering, fire up your regulated flashlights, turn on an AM radio, and you should hear an orchestra. /ubbthreads/images/graemlins/grin.gif

[ QUOTE ]
B@rt said:
CM,

[ QUOTE ]
markdi said:
yes I was joking

some times I can not stop my self

never grow up never grow old

[/ QUOTE ]

/ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/grin.gif

[/ QUOTE ]

Ooops /ubbthreads/images/graemlins/smile.gif B@rt, can you help me take both feet out of my mouth? /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif

CM

Aren't WinAMP visualizations just the coolest! Next best thing to licking those odd little tabs that that guy downtown sells for ten bucks apiece... /ubbthreads/images/graemlins/evilgrin07.gif