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PICList Thread
'555 as a clock'
1997\02\06@181907 by Mike Ghormley

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I am not very experienced with the PIC but here are my two cents anyway...

1) be sure that the fuse is set for an LP osc.

2) run the output of the 555 timer into the clock of a J/K flip-flop in
toggle mode to produce a 50% duty cycle.  Try the 74LS76 part and the
built-in Schmitt triggers will square up the wave nicely -- in case that is a
problem.

I think from previous experience with other parts that the duty cycle ans
non-square waves may be the culprits.  It was on other CPU's.

Remember that in the above situation the J/K FF is a divide by 2 circuit as
well.

Hello, I must be going...

Michael

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1997\02\06@222350 by Prashant Bhandary

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At 03:49 PM 6/02/97 -0800, you wrote:
>I am not very experienced with the PIC but here are my two cents anyway...
>
>1) be sure that the fuse is set for an LP osc.
>
>2) run the output of the 555 timer into the clock of a J/K flip-flop in
>toggle mode to produce a 50% duty cycle.  Try the 74LS76 part and the
>built-in Schmitt triggers will square up the wave nicely -- in case that is a
>problem.
>
>I think from previous experience with other parts that the duty cycle ans
>non-square waves may be the culprits.  It was on other CPU's.
>
>Remember that in the above situation the J/K FF is a divide by 2 circuit as
>well.
>

You can get a 50% duty cycle from a 555 by connecting the other end of the
charge+discharge resistor(R2) to the output. In other words, the cap is in its
usual place with pins 2 and 6 at one end and the other to ground. One end of
the resistor goes to pins 2 and 6 and the other end goes to pin 3. Pin 7 is
not connected and the second resistor is not required. I am not too sure
about the pin nos. The 555 was the only IC I knew about once but that was a
long time ago.

Regards

Prashant
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1997\02\07@001536 by *optoeng

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Prashant Bhandary wrote:
{Quote hidden}

....
NB:
This approach works well with CMOS 555s, but not too well with the
asymmetrical output of bipolar 555s.

--
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Paul Mathews, consulting engineer
AEngineering Co.

email: .....optoengKILLspamspam@spam@whidbey.com
non-contact sensing and optoelectronics specialists

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