74HC14 wired as R/C osc. With  diodes in the feedback path you can set
whatever duty cycle you like. 555 has the advantage of being able to
drive the LED directly (300mA output spec on the Signetics part IMS).
555's are also more stable w.r.t. temperature. 555C + vfet is lower
power solution.

Debbie Hynes wrote:
>
> PICers - i'm looking round for ideas to build an IR modulator cct. did a quick
> google but mostly fopund IR receivers.
>
> I'm using a 16f84 to drive an IR led but i'll need to modulate it at 38kbps. i
> guess i could use a 555 to gate the LED on/off - any other ideas?
>
> thankz 4 advice

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