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'[EE]: looking for retriggerable 555 monostable cir'
2006\03\30@123004 by Rob Robson

flavicon
face
I'm looking for a 555-based monostable (one-shot) circuit whose output will
STAY high as long as short negative-going pulses are present at the input.
The textbook 555 monostable circuit doesn't do this.  I have a spare NPN on
the board to utilize if necessary.  Has anyone come across a 555 circuit
that will do this?

Many thanks,
RR


2006\03\30@124509 by David VanHorn

picon face
You're looking for a retriggerable one shot, AKA "Missing pulse detector"
I've seen 555 ckts to do this, check an older National semi data book



On 3/30/06, Rob Robson <spam_OUTrobTakeThisOuTspamsilk.net> wrote:
{Quote hidden}

> -

2006\03\30@125138 by Peiserma

flavicon
face
piclist-bounces@mit.edu wrote:
> I'm looking for a 555-based monostable (one-shot) circuit
> whose output will STAY high as long as short negative-going
> pulses are present at the input.

I think the 74HC123 will do this. Once triggered, the output pulse can
be extended by retriggering. IIRC, it can be configured for either
positive or negative pulses.

2006\03\30@130442 by Bob Axtell

face picon face
I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5 as much, and
would be more reliable than a 555. Take about 5 minutes to write this code.

--Bob

David VanHorn wrote:

{Quote hidden}

>>-

2006\03\30@132511 by William Chops Westfield

face picon face

On Mar 30, 2006, at 9:29 AM, Rob Robson wrote:

> I'm looking for a 555-based monostable (one-shot) circuit whose
> output will STAY high as long as short negative-going pulses are
> present at the input. The textbook 555 monostable circuit doesn't
> do this.  I have a spare NPN on the board to utilize if
> necessary.  Has anyone come across a 555 circuit that will do this?
>
Google for "555 missing pulse detector" and you'll turn up a
standard schematic.  It uses an external PNP transistor to
discharge the cap...

BillW

2006\03\30@133146 by Rob Robson

flavicon
face
The problem is that I'm trying to fix a circuit that's already been
committed to PCB with the least ugly kludge possible.  It's like the Apollo
13 problem: trying to turn what you have into what you need.  What I have is
a 555 one-shot and an extra NPN transistor. What I need is a retriggerable
one-shot whose output goes high and stays high when the input receives
negative-going pulses, then goes low again once the pulses have been gone
for a second or two.  I'm looking at the inner workings of the 555 to try to
come up with a clever way to do this, but I'm running out of cleverness.  I
don't have access printed resources at the moment, and my Googling has yet
to expose a solution.  I'd be very grateful if anyone who has come across a
circuit that fits this description could pass it along.

RR



> I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5 as much, and
> would be more reliable than a 555. Take about 5 minutes to write this
> code.
>
> --Bob


2006\03\30@133341 by Wouter van Ooijen

face picon face
> I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5
> as much

dunno where you buy your 555's (or 10F's!), but I can still buy a bunch
of 555's for the price of one 10F. But if you include the components
around the 555 the price is probably the same. If you include the PCB
area and cost of placement... (but then you'd have to include the cost
of programming the 10F too).

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\03\30@141831 by Marcel duchamp

picon face
Rob Robson wrote:
> The problem is that I'm trying to fix a circuit that's already been
> committed to PCB with the least ugly kludge possible.  It's like the Apollo
> 13 problem: trying to turn what you have into what you need.  What I have is
> a 555 one-shot and an extra NPN transistor. What I need is a retriggerable
> one-shot whose output goes high and stays high when the input receives
> negative-going pulses, then goes low again once the pulses have been gone
> for a second or two.  I'm looking at the inner workings of the 555 to try to
> come up with a clever way to do this, but I'm running out of cleverness.  I
> don't have access printed resources at the moment, and my Googling has yet
> to expose a solution.  I'd be very grateful if anyone who has come across a
> circuit that fits this description could pass it along.
>
> RR

Rob, what you want is more easily found under the name of "missing pulse
detector".

Googling finds some similar ones:

http://www.uoguelph.ca/~antoon/circ/mispulse.htm


http://home.cogeco.ca/~rpaisley4/LM555.html#22




2006\03\30@142019 by David P Harris

picon face
See figure 10 here: <http://www.web-ee.com/primers/files/555AN.pdf>

Did that help?

David

Rob Robson wrote:

{Quote hidden}

2006\03\30@142212 by Robert Rolf

picon face
Or if the OP wants a no brainer hardware solution, 74HC221 retriggerable monostable.

If he want's to do it with 555, couple the short negative going pulse
into the timing cap using a diode so that the charge is pulled off
for every negative pulse and so the cap never reaches 2/3 Vcc to flop
the flip flop and activate 555 reset.
Use the negative pulse to trigger the 555 as well (sets the flip,
clearing reset and driving output high).

If the input signal can't handle the cap loading, they he'll have
to use the NPN to discharge the timing cap, and add another series
cap and R & Diode to ground to differentiate the incoming pulse and
turn the NPN on for long enough to reset the cap.

Robert

Bob Axtell wrote:

{Quote hidden}

>>>--

2006\03\30@142922 by Jay Shroff

picon face
Something like http://www.uoguelph.ca/~antoon/circ/mispulse.htm should work for you

-----Original Message-----
From: "Rob Robson" <.....robKILLspamspam.....silk.net>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Date: Thu, 30 Mar 2006 10:31:46 -0800
Subject: Re: [EE]: looking for retriggerable 555 monostable circuit

The problem is that I'm trying to fix a circuit that's already been
committed to PCB with the least ugly kludge possible.  It's like the Apollo
13 problem: trying to turn what you have into what you need.  What I have is
a 555 one-shot and an extra NPN transistor. What I need is a retriggerable
one-shot whose output goes high and stays high when the input receives
negative-going pulses, then goes low again once the pulses have been gone
for a second or two.  I'm looking at the inner workings of the 555 to try to
come up with a clever way to do this, but I'm running out of cleverness.  I
don't have access printed resources at the moment, and my Googling has yet
to expose a solution.  I'd be very grateful if anyone who has come across a
circuit that fits this description could pass it along.

RR



> I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5 as much, and
> would be more reliable than a 555. Take about 5 minutes to write this
> code.
>
> --Bob


2006\03\30@144441 by Rob Robson

flavicon
face
Looks ideal!  The absence of base resistor is a little surprising, but I'll
try it.  Thanks!

RR


> See figure 10 here: <http://www.web-ee.com/primers/files/555AN.pdf>
>
> Did that help?
>
> David
>


2006\03\30@145057 by Rob Robson

flavicon
face
Where do the extra "series cap and R and diode" go in this example?

Thx,
RR

Robert Rolf wrote:

{Quote hidden}

2006\03\30@145755 by Peiserma

flavicon
face
piclist-bounces@mit.edu wrote:
> The problem is that I'm trying to fix a circuit that's
> already been committed to PCB with the least ugly kludge
> possible.  

That makes it more interesting. Do you have the bare PCB, or is the
board already assembled? I don't suppose the 555 is a DIP package? If it
is, then one possibility would be building a "daughter board" that plugs
into where the 555 goes.

A wild thought: If there exists a small 8-pin micro (PIC or otherwise)
with Vdd and Vss on the same pins as the 555, you could swap that in.
Assuming its a 5V circuit.

2006\03\30@155406 by David P Harris

picon face
I have to state that retriggerable monostables are my favourite ICs!

These may not be best for him since he has restraints, but they can
handle signals of both polarities, and have complementary outputs, and
so are very useful.  The limited power supply range is a little
limiting, though.

David

Robert Rolf wrote:

{Quote hidden}

2006\03\30@184040 by Dwayne Reid

flavicon
face
At 12:44 PM 3/30/2006, Rob Robson wrote:
>Looks ideal!  The absence of base resistor is a little surprising, but I'll
>try it.  Thanks!

Don't be surprised at the lack of base resistor - its not
needed.  The PNP is configured as an emitter follower.

That said: there is a potential problem with the circuit.  If the
input remains LOW, the timer will never time out.  It will time out
only if the input remains HI for longer than the RC time constant.

If you need a true missing pulse detector, you'll need to
differentiate the pulse fed to the base of the PNP
transistor.  That's the extra RC network Rob Rolf mentioned.  Adding
that network will allow the monostable to time out and signal the
loss of input pulses regardless of whether the input is stuck HI or LO.

If you need to detect only the condition of the input stuck HI (the
condition of input stuck low is a "don't care"), the single added PNP
transistor is all that is needed.

dwayne

--
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Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2006\03\31@014623 by Luis.Moreira

picon face
Hi Rob,
Have a look at the CMOS 4538 we use it every where to detect loss of
signal very straightforward to use you set C and R to give you a pulse
width slightly longer than the ones you are detecting so they will keep
on retriggering the monostable so the output will be up while they are
there.
To deal with the negative pulses I would use a transistor (PNP probably)
or for less hassle an inverting op-amp with gain set at 1 or you can
even decide to condition the pulses with it.
This is the link for the datasheet:
http://www1.jaycar.com.au/images_uploaded/CD4538BC.PDF

But like some people said use a micro like that you can play with the
pulse width that you are detecting and the output of the circuit as much
as you can. I had a project where I needed a 250uS every 250mS, I first
used a 556 to generate the times and it was an absolute pain to get the
times right and then when I decide to change them even worse. So I
decided to use a micro to do it ( 68hc08) and I just built the circuit
and it took half hour to write the code, changing timing now is just
easy and I do not need to get the soldering iron out.
Hope it helps.
Best regards
               Luis  



{Original Message removed}

2006\03\31@132026 by Peter

picon face


On Thu, 30 Mar 2006 KILLspampeisermaKILLspamspamridgid.com wrote:

{Quote hidden}

12C508

Peter

2006\03\31@135022 by Mark Scoville

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face
Yes pins 1 & 8 are power for both a 555 and a 12C508 (at least the DIP
package). However, I think the power pins are flipped...

555 has +5 on pin 8 (referenced to pin 1)
12C508 has +5 on on pin 1 (referenced to pin 8)

I suppose you could put a 12C508 on the BOTTOM of the board. This would
align the power pins properly (assuming a DIP package). May or may not be
true for other packages.

-- Mark

> {Original Message removed}

2006\03\31@195306 by William Chops Westfield

face picon face
Getting back to the original question, it occurs to me that if
you can deal with an inverted output sense (that is, the output
stays LOW until there is a missing pulse), you can probably use
the "traditional" time-delay-from switch circuit (figure 8 from
http://www.uoguelph.ca/~antoon/gadgets/555/555.html )
This applies the trigger signal to the reset pin as well as
the trigger pin.  Some change in component values may be
needed; IIRC, this will charge the cap from 0 to 2/3 V instead
of sticking between 1/3 and 2/3 V...


>> A wild thought: If there exists a small 8-pin micro (PIC or
>> otherwise) with Vdd and Vss on the same pins as the 555, you
>> could swap that in. Assuming its a 5V circuit.
>>
For "traditional" 555 applications, you can fit a pic10f on a little
daughter card that would plug into a 555 socket, with power and
"digital" IO (trigger, output, reset) run to appropriate pins and
others left disconnected.  Indeed, I have several times played with
the idea of developing nice GUI (or otherwise human-oriented) PC
software where you plug in 555-like design parameters and get out
PIC code (or a programmed PIC, for that matter.)

However, you quickly run into the realization that there are MANY
places where even the cheapest microprocessors is NOT a good
replacement for a 555; the micro has very limited drive capability
and power supply limits. for instance, and applications that
are not quite "standard" are distressingly common...

BillW


'[EE]: looking for retriggerable 555 monostable cir'
2006\04\02@031637 by Vasile Surducan
face picon face
On 3/30/06, Bob Axtell <spamBeGoneengineerspamBeGonespamcotse.net> wrote:
> I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5 as much, and
> would be more reliable than a 555. Take about 5 minutes to write this code.

Bob,
Anyway or anyhow you're looking , 555 is cheapest than any microcontroller.
Usually 10x555 = 1cheap microcontroller, as price.
Output curent capability of a 555 is greatest than any IO.
Not talking you have to write the code, or if you want ONE monostable
this is waste of time.
However there is one problem with 555 monostable: the first false
trigger at power up.

greetings,
Vasile


{Quote hidden}

2006\04\02@121946 by Bob Axtell

face picon face
Vasile Surducan wrote:

>On 3/30/06, Bob Axtell <RemoveMEengineerspamTakeThisOuTcotse.net> wrote:
>  
>
>>I'd do it with a PIC10F20X. It would be 1/10 size, cost 1/5 as much, and
>>would be more reliable than a 555. Take about 5 minutes to write this code.
>>    
>>
>
>Bob,
>Anyway or anyhow you're looking , 555 is cheapest than any microcontroller.
>Usually 10x555 = 1cheap microcontroller, as price.
>Output curent capability of a 555 is greatest than any IO.
>Not talking you have to write the code, or if you want ONE monostable
>this is waste of time.
>However there is one problem with 555 monostable: the first false
>trigger at power up.
>
>  
>
I don't agree. The 555 itself costs about 0.25 USD, but the capacitors
and resistors
and extra transistor to create a reliable retriggerable circuit easily
pushes it over  $1.50
USD. I can buy the PIC10F200 for $0.50 USD in 100 qty.

He didn't say he wanted ONE. He said he wanted to correct a problem on a
already-laid-out
production PCB. PLUS, It has no power-up glitches.  and will run with an
accuracy of 3%
WORST-CASE, 1% typical.

The code is about 20 code words. I will write it myself if he wants.

--Bob

--
Note: To protect our network,
attachments must be sent to
attachEraseMEspam.....engineer.cotse.net .
1-520-850-1673 USA/Canada
http://beam.to/azengineer

2006\04\02@161831 by Peter

picon face


On Fri, 31 Mar 2006, Mark Scoville wrote:

> Yes pins 1 & 8 are power for both a 555 and a 12C508 (at least the DIP
> package). However, I think the power pins are flipped...
>
> 555 has +5 on pin 8 (referenced to pin 1)
> 12C508 has +5 on on pin 1 (referenced to pin 8)
>
> I suppose you could put a 12C508 on the BOTTOM of the board. This would
> align the power pins properly (assuming a DIP package). May or may not be
> true for other packages.

The pins can be turned 'inside out' but bottom mounting is valid ;-)

Peter

2006\04\03@045056 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: EraseMEpiclist-bouncesspammit.edu [RemoveMEpiclist-bouncesEraseMEspamEraseMEmit.edu]
>Sent: 02 April 2006 17:20
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE]: looking for retriggerable 555 monostable circuit
>
>
>>  
>>
>I don't agree. The 555 itself costs about 0.25 USD, but the capacitors
>and resistors
>and extra transistor to create a reliable retriggerable circuit easily
>pushes it over  $1.50
>USD. I can buy the PIC10F200 for $0.50 USD in 100 qty.

You must use very expensive components!  Generic small signal bipolars are what, a few cents each?  Resistors < 1 cent in any reasonable quantity, leaving only the timing and decoupling caps.  Should be doable for well under $0.50 total IMO.  Of course, the price does rise considerably if timing demands mean that precision R's and C's need to be used.

Regards

Mike

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2006\04\03@194638 by Vasile Surducan

face picon face
On 4/2/06, Bob Axtell <RemoveMEengineerspam_OUTspamKILLspamcotse.net> wrote:
{Quote hidden}

NE555 is here 0.1EUR/1pcs. There is no need for any external
transistor and RC components are really free.
But I can't kidnap your pleasure of using a PIC in everything (even is
worthing or not),  so let say you have right.
:)

Vasile


{Quote hidden}

> -

2006\04\03@203428 by William Chops Westfield

face picon face

On Apr 3, 2006, at 4:46 PM, Vasile Surducan wrote:

> NE555 is here 0.1EUR/1pcs.

I wish I had your distributers, then.  Here, we have radio
shack at $1.69 (CMOS version only), Digikey at about $0.40,
and Jameco at $0.29.  Even digikey's 10k piece price is a
bit more than $0.11...

BillW

2006\04\04@042708 by Vasile Surducan

face picon face
On 4/4/06, William Chops Westfield <RemoveMEwestfwKILLspamspammac.com> wrote:
>
> On Apr 3, 2006, at 4:46 PM, Vasile Surducan wrote:
>
> > NE555 is here 0.1EUR/1pcs.
>
> I wish I had your distributers, then.  Here, we have radio
> shack at $1.69 (CMOS version only), Digikey at about $0.40,
> and Jameco at $0.29.  Even digikey's 10k piece price is a
> bit more than $0.11...

Digikey is a killing source.
I'm buying from http://www.comet.srl.ro/main/index.html
try a NE555 search.
If would be more expensive no one will buy nothing here.
Beying a poor country has some advantages.
Also being out from EU as long as possible (god help us...)

greetings
Vasile

2006\04\04@132147 by Spehro Pefhany

picon face
At 11:27 AM 4/4/2006 +0300, you wrote:

>Digikey is a killing source.
>I'm buying from http://www.comet.srl.ro/main/index.html
>try a NE555 search.
>If would be more expensive no one will buy nothing here.
>Beying a poor country has some advantages.
>Also being out from EU as long as possible (god help us...)

Here's the worst place I found in a quick web search:

http://www.micronica.com.au/~micronica/pricelist/chips.htm

US 8.00 each with a US$40 plus delivery minimum, and shipping $30 or $45US.

;-)  You can get 500 fresh Fairchild RoHS-compliant parts from Mouser
(including shipping) for about the price of 5 dusty parts from them.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffSTOPspamspamspam_OUTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2006\04\04@151912 by Sergey Dryga

face picon face
Spehro Pefhany <speff <at> interlog.com> writes:

<SNIP>
> Here's the worst place I found in a quick web search:
>
> www.micronica.com.au/~micronica/pricelist/chips.htm
>
> US 8.00 each with a US$40 plus delivery minimum, and shipping $30 or $45US.
>
>   You can get 500 fresh Fairchild RoHS-compliant parts from Mouser
> (including shipping) for about the price of 5 dusty parts from them.
>
> >Best regards,
>
> Spehro Pefhany --"it's the network..."            "The Journey is the reward"
> speff <at> interlog.com             Info for manufacturers:
http://www.trexon.com
> Embedded software/hardware/analog  Info for designers:  http://www.speff.com
> ->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff
>
They probably do not have any stock at all.  At this prices, they can get next
day FedEx from Mouser and then ship it to a customer and still make profit.  
Probably not many customers though.  But as the saying goes: there is a sucker
born every minute...

Sergey



2006\04\04@174320 by Peter

picon face

On Mon, 3 Apr 2006, William Chops Westfield wrote:

> On Apr 3, 2006, at 4:46 PM, Vasile Surducan wrote:
>
>> NE555 is here 0.1EUR/1pcs.
>
> I wish I had your distributers, then.  Here, we have radio
> shack at $1.69 (CMOS version only), Digikey at about $0.40,
> and Jameco at $0.29.  Even digikey's 10k piece price is a
> bit more than $0.11...

The 555 is 1/10 of what you pay for it but their incomes are 1/20 of
your income. So the 555 is twice as expensive to them than it is to
you ...

Peter

2006\04\04@235353 by Vasile Surducan

face picon face
On 4/5/06, Peter <spamBeGoneplpSTOPspamspamEraseMEactcom.co.il> wrote:
>
> On Mon, 3 Apr 2006, William Chops Westfield wrote:
>
> > On Apr 3, 2006, at 4:46 PM, Vasile Surducan wrote:
> >
> >> NE555 is here 0.1EUR/1pcs.
> >
> > I wish I had your distributers, then.  Here, we have radio
> > shack at $1.69 (CMOS version only), Digikey at about $0.40,
> > and Jameco at $0.29.  Even digikey's 10k piece price is a
> > bit more than $0.11...
>
> The 555 is 1/10 of what you pay for it but their incomes are 1/20 of
> your income. So the 555 is twice as expensive to them than it is to
> you ...

Peter,
he can't understand that. He must become romanian for a while so the
above phrase have some sense.
:)

greetings,
Vasile

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