Strobe effect from LED regulation

PhotonWrangler · Jan 19, 2006

I discovered something by accident the other day. I'm sitting in front of this PC with the side panel off, and when I grabbed a nearby Dorcy 1AA to look at something on the motherboard, I realized that I could read the AMD logo on the center of the fan even though it spins at 2600rpm! Hmm.

Tried a non-regulated flashlight and the logo was just a blur.

Tried my Q-III and I can read it. Same for another regulated light as well as a nearby CFL.

Call me easily amused...

Navck · Jan 19, 2006

Might just be the PWM right?

PhotonWrangler · Jan 20, 2006

Navck said:
Might just be the PWM right?

Exactly. What's interesting is that the logo sits still regardless of the type of regulated flashlight (and thus PWM frequency). I would have expected slightly different results for different "strobing" repetition rates.

hyperslug · Jan 20, 2006

The PWM frequencies don't necessarily have to be the same, as long as they sample the fan at the correct multiples. If the fans frequency is 43Hz, then lights that sample at 21.5Hz or 10.25Hz would display that effect.

I think. Someone with a DSP background feel free to jump in.

Still, very strange.

xenopus · Jan 20, 2006

Insufficient output capacitor perhaps, or capacitor omitted for cost savings

Piers!

PhotonWrangler · Jan 20, 2006

hyperslug said:
The PWM frequencies don't necessarily have to be the same, as long as they sample the fan at the correct multiples. If the fans frequency is 43Hz, then lights that sample at 21.5Hz or 10.25Hz would display that effect.

I think. Someone with a DSP background feel free to jump in.

Still, very strange.

Yes, it occurred to me that any harmonic of the fundamental frequency would cause the iumage to sit still. Now there's got to be something useful
that I can do with this information...
:thinking:

Strobe effect from LED regulation

PhotonWrangler

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Navck

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PhotonWrangler

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hyperslug

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xenopus

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PhotonWrangler

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