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'[pic]: PIC vs. 555'
2004\06\01@222912 by Mike Hord

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Not to mention the PITA that getting a 50% duty cycle at the exact
frequency you want, or getting a duty cycle above 50% (right?  Over
50% requires a diode, right?).

So let's add the parts count up:

PIC Based- 1 PIC, 1 decoupling cap.
555- at worst, 1 diode, two caps, three resistors, 555.  At best,
            555, two caps, two resistors.

Of course, the PIC has to be programmed, can only drive up to 25 mA,
and is limited to integer multiple of 1 uS, and can only run up to a bit
more than 5 volts.  OTOH, you could do multiple frequencies with one
chip, or at least have the complement available.

All in all, no, a PIC is not ALWAYS a replacement for a 555, but it can
be a great replacement for it in the right situation.

Mike H.

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2004\06\01@231140 by M. Adam Davis

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Under 50% requires a diode:
http://www.williamson-labs.com/555-circuits.htm

What I want is a replacement for the venerable lm3909.  I suppose one
could modify the joule thief for this with an extra cap, perhaps a zener...

-Adam

Mike Hord wrote:

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2004\06\02@031749 by Peter Moreton

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Yeah, I still have a few LM3909's blinking LED's scattered about the house.
There is something highly 'kewl' about an LED that flashes (very brightly)
for 5 years on one D-cell. I wish they still made these IC's

Peter Moreton

> {Original Message removed}

2004\06\02@032204 by hael Rigby-Jones

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>-----Original Message-----
>From: Mike Hord [spam_OUTgaidinmdTakeThisOuTspamHOTMAIL.COM]
>Sent: 02 June 2004 03:28
>To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
>Subject: [pic]: PIC vs. 555
>
>
>Not to mention the PITA that getting a 50% duty cycle at the
>exact frequency you want, or getting a duty cycle above 50%
>(right?  Over 50% requires a diode, right?).

50% is easy, you just use the output pin to charge/discharge the timing cap
via a resistor rather than using the normal pins.  The only downside of this
is that frequency stability isn't as good if the output pin is loaded by a
varying amount.

Regards

Mike




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2004\06\02@171530 by Peter L. Peres

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> What I want is a replacement for the venerable lm3909.

Hehe. Wait for the MAX3909 ? ;-)

Peter

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