> > An IR data stream from a dedicated IR transmitter IC will have
> > a pretty accurate data clock.
>
> Not in my experience. They tend to be RC based and will drift
> a fair amount. There is measurable drift over the length of a
> transmission but not enough to cause too much trouble.

Those I've been familiar with have at minimum a 455kHz resonator
as the clock source. All operations of, and data from, the IC are
based on Tosc. They have different formats for data streams, eg
pulse-width (say 10 x Tosc for "0" and 5 x Tosc for "1") or the
more conventional "0" & "1" level equi-time bits like RS comms
>
> You also have to watch the rise and fall times of some IR
> detectors. They aren't the same so measuring a pulse width gives
> you wrong information, but edge to edge is OK.

Using a 3-terminal (inverting) receiver-filter-amplifier like the Sharp
IS1U60, particularly if the data is sent with a 38kHz carrier, makes
for a pretty good long-range reliable transfer. Nice clean edges and
ambient light immunity. Alternatively an IR diode and LP311 work
well together for a lower cost short-range application

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