Lindy,

I may be wrong but it seems that to get 10 uSec and 1 Sec you need 10megohm=
 for R1, 100 ohms for R2 and .15uFd,
But I guess that gives the wrong duty cycle (1 sec on, 10 uSec off, so you =
would need to rig a 1 transistor inverter from the output.=20
See calculator at=20
http://www.talkingelectronics.com/projects/555/Page2-555.html
Since no one has mentioned this approach, I suspect I may be wrong. Input w=
elcome.

Or you could use the two resistors and one diode hooked up from the output =
pin to the timing cap. I can't find the circuit I want to show you but look=
 at=20
http://www.learnabout-electronics.org/Oscillators/osc44.php   fig 4.4.8
And leave out R3 and VR1.  Hook R1 and R2 to output, probably something lik=
e R1 =3D 100 ohm and R2=3D10 megohm=20

Also, If hooking up to a R..Pi, could you use the Pi for the 1 sec function=
 and the 555 for the 10 uSec function.

At 09:28 AM 12/11/2013, Lindy Mayfield wrote:
>I wanted to try to create an analogue circuit that would trigger a=20
>sonic range finder (SR04) so that I could check things out with a=20
>scope.  It requires a 10us pulse to start it.  (Then the output line=20
>goes high relative to the distance.)  I don't think I have the=20
>ability (yet) to do much more with it though.  The intent is to=20
>connect it to a Pi.
>
>What I wanted was a 10us pulse every second or so, and I found a=20
>handy 555 laying around.  However, using the nice calculator I found=20
>below, I couldn't manage to get anywhere near the results I wanted=20
>no matter what I put in.   (The largest capacitor I have is 100=20
>uF.)  Is this possible?  I know it should be.
>
>Thank you!
>Lindy

Looking forward,
Al Shinn
--=20
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