At 11:34 PM 3/14/01 +0100, you wrote:
>I have finished a IR proximity sensor with a 556 (<=> 2x555),
>an IR led and an IS1U60. In order to save mA I need to reduce
>the duty cycle of my 555's.
>
>Somebody knows how to make a 555 oscillate with a duty cycle
>smaller thab 0.5 ?
>
>Note : duty cycle = ratio of the time duration when the ouput
>pulse is high to the total period.

One way is to leave 7 open, connect 2 & 6 together & to cap,
as usual, and connect two resistors in series with diodes,
back to back between 2&6 and 3. This works better with
CMOS 555 and output lightly loaded.



6 & 2 --x----|<|----- R1 -----x--- 3
        |                     |
        x----|>|------R2 -----x

Ton = k * R1
Toff = k * R2

Duty cycle = Ton/(Ton+Toff) = k * (R1/(R1+R2))

So, just make R1 < R2 to get < 50% duty cycle

Best regards,
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