On Mon, 12 Aug 2002, Spehro Pefhany wrote:

>NS patented a neat way of calibrating LED watches way back, they used the
>mux frequency of the display as a non-contact way of transmitting the
>frequency externally. You could do that with the "power on" LED in a product,
>just run it at 50% duty cycle at 4MHz and use a PIN photodiode to pick up
>the signal. Visible LEDs typically switch in around 100ns, so that should
>not be a problem.

Neat, however good luck passing emissions certification with a device
that has a 4MHz 30mW radiator on it (in H field at least). Maybe one could
put it into jig mode using a jumper and output a slower clock (a few kHz).

Peter

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