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'[EE] : 555 as Bistable'
2000\10\10@153255 by ?=

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   Hello all:

   Does anybody have an schematich of how to use a 555 as a bistable?

   I looked in to datasheets but I couldn't find it there, also the Net
same result...

   Thanks in advance,

   Gonzalo

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2000\10\10@172419 by James Paul

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Gonzalo,

As far as I can remember, you can't use a 555 as a bistable.
Only monostable or astable.  Due to the fact that it is a
timer, you want the output in one state, and then switch to the
other state when the timer runs out in the case of a monostable.
In the case of an astable, you want it to repeatedly switch states.
But in no way can you put in in one state, and have it remain there
forever or until you switch to the opposite state.

If you want a bistable, choose a 7474 or the CMOS equivalent.

Hope this helps you out.


                                           Regards,

                                             Jim




On Tue, 10 October 2000, Gonzalo Jiminez Yamasaki wrote:

{Quote hidden}

spam_OUTjimTakeThisOuTspamjpes.com

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2000\10\11@033513 by Caisson

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> Van: Gonzalo Jiménez Yamasaki              <.....gonzalo.jimenezKILLspamspam@spam@CONTROLMATIC.COM>
> Aan: PICLISTspamKILLspamMITVMA.MIT.EDU
> Onderwerp: [EE] : 555 as Bistable
> Datum: dinsdag 10 oktober 2000 21:38
>
>     Hello all:

Hello Gonzalo,

>     Does anybody have an schematich of how to use a 555 as a bistable?
>
>     I looked in to datasheets but I couldn't find it there, also the Net
> same result...

Well, Allmost no-one tries to do it ...  That's due to the problem that a
555 contains a Flip-flop (and therefore is a Bi-stable element), but has
got it's "Set" input inverted.

This means that a Stable condition will be reached if "Clear" (pin 2) is
High, and "Set" (pin 6) is Low.

There are several possibilities to get this condition, such as a
contact-making button for pin 2 , and a contact-breaking button for pin 6
(both with a pull-up resistor)

Regards,
 Rudy Wieser

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2000\10\11@034314 by Maurizio Viterbini

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Gonzalo Jiménez Yamasaki wrote:

>     Hello all:
>
>     Does anybody have an schematich of how to use a 555 as a bistable?
>
>     I looked in to datasheets but I couldn't find it there, also the Net
> same result...
>
>     Thanks in advance,
>
>     Gonzalo
>
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> (like ads or off topics) for you. See http://www.piclist.com/#topics

Ciao Gonzalo, I suggest to try this schema (from an old idea on EDN Oct 5
1974 R.L.Gephart):
Connect  pull-up resistors 4.7K to pins 2 and 4 (Trig and Res) , connect pin
1 to pin 6 , connect any R to pin 3.
The SET action will be performed switching  pin 2 to GND, RESET switching
pin 4.



Maurizio Viterbini
Istituto di Fisica dell'Atmosfera
Via Fosso del Cavaliere 100
00133 Roma
Italy

tel. +39 06 49934200
fax +39 06 20660291
email .....viterbinKILLspamspam.....ifa.rm.cnr.it

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2000\10\11@151109 by w. v. ooijen / f. hanneman

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>  As far as I can remember, you can't use a 555 as a bistable.

A bistable is a circuit that can be in either of two modes and will then
remain in that mode. The 555 clearly has that ability: in astable mode for
a certain voltage on the C the C is either being charged or being
discharged. In an astable there is (negative) feedback so eventually the
each mode turns into the other mode, but if you remove the feedback, tie
the sense to a 0.5 Vcc (I think the switch thresholds are 1/3 and 2/3) you
have a bistable. Making the sense high (for a short time) starts one mode,
making it low starts the other.

Wouter

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2000\10\11@190842 by me

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The 555 can be used as a bistable of sorts by connecting a single resistor
between the output and the trigger input. The discharge output is /Q the output
is Q, threshold can be used to force state (esp. reset). The normal input is
through a small capacitor into the trigger input. It can be used as a touch
switch (CMOS 555 and Rfeedback > 2M2). In this case there are two 'meshed'
type touchpads, one supplies +Vcc to trigger through 100K, the other GND. It
can also debounce switches etc.

There are other tricks that can be played using separate +trig and -trig
inputs and Q and /Q (the later with a pullup).

hope this helps ;-)

Peter

PS: There is a book full of 555 circuits but I don't remember where I saw it.
The ideas above are NOT from that book.

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