555 timer
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Posts: 46,084
Do you really need a square wave? The basic astable uses 2 resistors and a
cap. Call the resistor to Vcc, Ra, and the one between Threshold and
Discharge, Rb. Duty cycle (output high/total cycle time) is
(Ra+Rb)/(Ra+2Rb)
So the 555 "likes" duty cycles greater than 50%. Getting 50% or less is the
problem. A diode across Rb (pointing away from Discharge) alters the duty
cycle to approximately
Ra/(Ra+Rb)
which allows very small duty cycles. The disadvantage is that the diode
will degrade temperature sensitivity. As Mike pointed out, the 555 is
reasonably stable when used with good resistors and caps.
Ray McArthur
>>It's been a while since I tried to use a 555 for anything serious (not
since Stamp 1, at least), but as I remember it, you can't get a square wave
from the usual two resistor-one capacitor configuration. The capacitor
charges through two resistors and discharges through only one. I think Don
Lancaster had a trick that used a diode across the pin 6 - pin 7 resistor
that allowed you to make it square, but the frequency tuning would then
require adjusting both resistors. I also recall that I quit using the
standard 555 in favor of the CMOS part (7555 or something like that). And
remember to put a cap on pin 5 for stabilization.
Just my $.02 worth and maybe only worth half of that!<<
cap. Call the resistor to Vcc, Ra, and the one between Threshold and
Discharge, Rb. Duty cycle (output high/total cycle time) is
(Ra+Rb)/(Ra+2Rb)
So the 555 "likes" duty cycles greater than 50%. Getting 50% or less is the
problem. A diode across Rb (pointing away from Discharge) alters the duty
cycle to approximately
Ra/(Ra+Rb)
which allows very small duty cycles. The disadvantage is that the diode
will degrade temperature sensitivity. As Mike pointed out, the 555 is
reasonably stable when used with good resistors and caps.
Ray McArthur
>>It's been a while since I tried to use a 555 for anything serious (not
since Stamp 1, at least), but as I remember it, you can't get a square wave
from the usual two resistor-one capacitor configuration. The capacitor
charges through two resistors and discharges through only one. I think Don
Lancaster had a trick that used a diode across the pin 6 - pin 7 resistor
that allowed you to make it square, but the frequency tuning would then
require adjusting both resistors. I also recall that I quit using the
standard 555 in favor of the CMOS part (7555 or something like that). And
remember to put a cap on pin 5 for stabilization.
Just my $.02 worth and maybe only worth half of that!<<
Comments
>Do you really need a square wave? The basic astable uses 2 resistors and a
>cap. Call the resistor to Vcc, Ra, and the one between Threshold and
>Discharge, Rb. Duty cycle (output high/total cycle time) is
>
>(Ra+Rb)/(Ra+2Rb)
>
>So the 555 "likes" duty cycles greater than 50%. Getting 50% or less is the
>problem. A diode across Rb (pointing away from Discharge) alters the duty
>cycle to approximately
>
>Ra/(Ra+Rb)
>
> which allows very small duty cycles. The disadvantage is that the diode
>will degrade temperature sensitivity. As Mike pointed out, the 555 is
>reasonably stable when used with good resistors and caps.
You can get 50% duty cycle very easily if you use a CMOS 555 - and it takes
fewer parts than the standard design. Build the oscillator as follows:
pins 2&6 tied to the timing capacitor and connect the timing resistor from
the timing cap to the output pin (pin 3). Voila! Equal HI and LO
periods! Pin 7 is not used in this configuration and can be used if an
open drain output is useful anywhere. And, of course, the usual output of
pin 3 is also available.
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 16 years of Engineering Innovation (1984 - 2000)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.
Ray McArthur
Original Message
From: Dwayne Reid <dwayner@p...>
To: <basicstamps@egroups.com>
Sent: Thursday, December 07, 2000 10:10 PM
Subject: Re: [noparse][[/noparse]basicstamps] 555 timer
> You can get 50% duty cycle very easily if you use a CMOS 555 - and it
takes
> fewer parts than the standard design. Build the oscillator as follows:
> pins 2&6 tied to the timing capacitor and connect the timing resistor from
> the timing cap to the output pin (pin 3). Voila! Equal HI and LO
> periods! Pin 7 is not used in this configuration and can be used if an
> open drain output is useful anywhere. And, of course, the usual output of
> pin 3 is also available.
>
symmetrical voltage swing because of the NPN transistor output
stage. Typical output swing at 5V is 0.2V (LO) and 4V (HI). That would
result in a 15% or so difference between HI and LO period. That's why
Signetics designed in that pin 7 open collector output and came up with the
standard configuration that everyone uses - it trades an uncertain 15% duty
cycle error with a non-ideal but definable duty cycle. It was appropriate
for the technology of the era.
The modern CMOS parts have symmetrical voltage swing which allows the
output pin to be used as the feedback node for a nominal 50% duty cycle.
dwayne
At 12:10 AM 12/8/00 -0500, Ray McArthur wrote:
>Great idea, Dwayne. Shouldn't it also work with a standard (non-CMOS) part?
>
>Ray McArthur
>
>
Original Message
>From: Dwayne Reid <dwayner@p...>
>To: <basicstamps@egroups.com>
>Sent: Thursday, December 07, 2000 10:10 PM
>Subject: Re: [noparse][[/noparse]basicstamps] 555 timer
> > You can get 50% duty cycle very easily if you use a CMOS 555 - and it
>takes
> > fewer parts than the standard design. Build the oscillator as follows:
> > pins 2&6 tied to the timing capacitor and connect the timing resistor from
> > the timing cap to the output pin (pin 3). Voila! Equal HI and LO
> > periods! Pin 7 is not used in this configuration and can be used if an
> > open drain output is useful anywhere. And, of course, the usual output of
> > pin 3 is also available.
> >
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 16 years of Engineering Innovation (1984 - 2000)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.
>>takes
>> > fewer parts than the standard design. Build the oscillator as follows:
If a pure 50% duty cycle is required and one more part isn't a problem, then
double
the 555's frequency and clock a D flip-flip with it. Feed the _Q back into
D and take
your output from Q. Every time the clock input goes high, the flip-flip
toggles. The
555 duty cycle could be anything with this setup.
just a quick question on using the 555 timer as a monostable
multivibrator with my basic stamp 2sx. im using an annemometer which
trips a switch every rotation. the pulses can be of random duration
and frequency depending on the wind speed. the stamp is reading the
trips fine with just a resistor and capacitor in parallel but could i
use a monostable multivibrator to give me constant pulse durations
which might ensure greater reliablity for the stamp reading the trips.
Thank you
a one-shot and configure the RC components to get the pulse width you
want. You could also use the Reset input of the 555 to clear an input
once you've seen it (this requires a second pin from you BASIC Stamp).
-- Jon Williams
-- Parallax
Original Message
From: fearghaloconnor [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=IyVwtW2XlTBGa-azOgKE-a7jpLjGA0V0KMf3mz9jQ7fiuKsC6MCVhTHY0Ua4BZNROg85ZSQrA5Om32EgNuZbNBYoIbc]fearghaloconnor@y...[/url
Sent: Tuesday, March 02, 2004 10:37 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] 555 timer
hi,
just a quick question on using the 555 timer as a monostable
multivibrator with my basic stamp 2sx. im using an annemometer which
trips a switch every rotation. the pulses can be of random duration
and frequency depending on the wind speed. the stamp is reading the
trips fine with just a resistor and capacitor in parallel but could i
use a monostable multivibrator to give me constant pulse durations
which might ensure greater reliablity for the stamp reading the trips.
Thank you
length output pulse regardless of the width of the trigger pulse.
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: fearghaloconnor [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=BKa2BNeJA2LVEV38is-HsUe701N0sM8zFqjdq87JcVjYOV0no3rVaeX-qdSTO31C0KSB5_zGZAfb3EckA-yQyqU]fearghaloconnor@y...[/url
Sent: Tuesday, March 02, 2004 11:37 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] 555 timer
hi,
just a quick question on using the 555 timer as a monostable
multivibrator with my basic stamp 2sx. im using an annemometer which
trips a switch every rotation. the pulses can be of random duration
and frequency depending on the wind speed. the stamp is reading the
trips fine with just a resistor and capacitor in parallel but could i
use a monostable multivibrator to give me constant pulse durations
which might ensure greater reliablity for the stamp reading the trips.
Thank you
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> just a quick question on using the 555 timer as a monostable
>multivibrator with my basic stamp 2sx. im using an annemometer which
>trips a switch every rotation. the pulses can be of random duration
>and frequency depending on the wind speed. the stamp is reading the
>trips fine with just a resistor and capacitor in parallel but could i
>use a monostable multivibrator to give me constant pulse durations
>which might ensure greater reliablity for the stamp reading the trips.
> Thank you
Why tinker with it if it already works? The COUNT command--Is that
what you're using?--does not care about the pulse width so long as it
is longer than 2 microseconds on the 'sx. The problem for
reliability with the reed switch in the anemometer is contact bounce,
and the RC should take care of that.
-- Tracy
from a Davis Model 7911 Anemometer for several years. I use the COUNT
command. The anemometer is designed such that 2.308 seconds of counts
will translate directly to windspeed in MPH. The command line is:
COUNT, InputPin, 5770, WindSpeed (5770 = 2.308 sec for BS2sx)
I feed the output from the reed switch through a small RC filter then
directly into the Stamp pin. It seems to work fine without any
additional pulse-forming.
Dave
--- In basicstamps@yahoogroups.com, "fearghaloconnor"
<fearghaloconnor@y...> wrote:
> hi,
> just a quick question on using the 555 timer as a monostable
> multivibrator with my basic stamp 2sx. im using an annemometer which
> trips a switch every rotation. the pulses can be of random duration
> and frequency depending on the wind speed. the stamp is reading the
> trips fine with just a resistor and capacitor in parallel but could i
> use a monostable multivibrator to give me constant pulse durations
> which might ensure greater reliablity for the stamp reading the trips.
> Thank you
minutes in a monostable configuation with no additional IC's?
Thanks,
Chris
CHRIS@R... writes:
Does anyone know if it's possible to have the 555 delay for 55
minutes in a monostable configuation with no additional IC's?
Thanks,
Chris
If it is, that would be some honker capacitors and resistors. I have never
seen one configured for anywhere near that long.
Randy Abernathy
4626 Old Stilesboro Road
Acworth, GA 30101
Ph / Fax: 770-974-5295
E-mail: cnc002@a...
I furnish technical support, repair, and other related services for your
industrial woodworking machinery. My background as Senior Service Engineer for the
SCMI Group for nearly fifteen years with factory training, combines with my
extensive background in electronics, mechanics, pneumatics, electrical and CNC
machinery to offer you needed support for your machinery.
[noparse][[/noparse]Non-text portions of this message have been removed]
longer than that and fingerprints on the board and capacitor leakage become
a problem. There are other ics that you can use that will do longer. Or
write a timer loop in the basic stamp routine<G>.
Original Message
From: christopher41877 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=IZSamnzM0n4mI8eXSHeAOyDqeuoNc5XB4sYqg1fUC-253qzhO3diRGsXhgL4cJae3-aVbyjIfH6Ka4Kw39e5cFtEaA0]CHRIS@R...[/url
Sent: Thursday, July 15, 2004 12:46 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] 555 Timer
Does anyone know if it's possible to have the 555 delay for 55
minutes in a monostable configuation with no additional IC's?
Thanks,
Chris
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anyone have an idea to time 50 minutes?
--- In basicstamps@yahoogroups.com, cnc002@a... wrote:
> In a message dated 7/15/2004 4:46:48 PM Eastern Standard Time,
> CHRIS@R... writes:
> Does anyone know if it's possible to have the 555 delay for 55
> minutes in a monostable configuation with no additional IC's?
>
> Thanks,
>
> Chris
> If it is, that would be some honker capacitors and resistors. I
have never
> seen one configured for anywhere near that long.
>
> Randy Abernathy
> 4626 Old Stilesboro Road
> Acworth, GA 30101
> Ph / Fax: 770-974-5295
> E-mail: cnc002@a...
>
> I furnish technical support, repair, and other related services
for your
> industrial woodworking machinery. My background as Senior Service
Engineer for the
> SCMI Group for nearly fifteen years with factory training,
combines with my
> extensive background in electronics, mechanics, pneumatics,
electrical and CNC
> machinery to offer you needed support for your machinery.
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
http://www.semiconductors.philips.com/pip/XICM7555CCU.html
RR
--- In basicstamps@yahoogroups.com, "christopher41877" <CHRIS@R...>
wrote:
> I won't be able to use the stamp to do this timing function, does
> anyone have an idea to time 50 minutes?
>
>
> --- In basicstamps@yahoogroups.com, cnc002@a... wrote:
> > In a message dated 7/15/2004 4:46:48 PM Eastern Standard Time,
> > CHRIS@R... writes:
> > Does anyone know if it's possible to have the 555 delay for 55
> > minutes in a monostable configuation with no additional IC's?
> >
> > Thanks,
> >
> > Chris
> > If it is, that would be some honker capacitors and resistors. I
> have never
> > seen one configured for anywhere near that long.
> >
> > Randy Abernathy
> > 4626 Old Stilesboro Road
> > Acworth, GA 30101
> > Ph / Fax: 770-974-5295
> > E-mail: cnc002@a...
> >
> > I furnish technical support, repair, and other related services
> for your
> > industrial woodworking machinery. My background as Senior Service
> Engineer for the
> > SCMI Group for nearly fifteen years with factory training,
> combines with my
> > extensive background in electronics, mechanics, pneumatics,
> electrical and CNC
> > machinery to offer you needed support for your machinery.
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
>Does anyone know if it's possible to have the 555 delay for 55
>minutes in a monostable configuation with no additional IC's?
Sure, with a CMOS 555 and top quality R/C parts, time delays
of several hours are easily possible with a 555. BTDT decades ago...
You need GOOD quality low leakage caps and the highest value
timing resistor your 555 will allow.
The problem isn't delay time... it's stability. Especially over
temperature.... the leakage of the large capacitor is likely to
vary quite a bit with temperature, and make your timing drift
all over.
If you can operate in a temperature controlled environment you'll
have a *big *advantage.
If you really need to hit 55 minutes ACCURATELY and
CONSISTENTLY, a 555 isn't the way. If you need approximately
55 minutes, and 52 or 61 would be acceptable, with an average
of 55 minutes then that's easily doable... Again, top quality R/C parts
are the key... you ain't gonna get 1% accuracy with 10% tolerance
parts... especially over any kind of temperature variation....
Did you know the 555 was first introduced in 1971?
The little sucker has been in production for 33 years now. Amazing!
Steve D. - 555 user since 1974...
[noparse][[/noparse]Non-text portions of this message have been removed]
http://home.cogeco.ca/~rpaisley4/LM555.html
It has a lot of examples and a handy MONOSTABLE OSCILLATOR CALCULATOR
>From: laurasdog@w...
>Reply-To: basicstamps@yahoogroups.com
>To: basicstamps@yahoogroups.com
>Subject: Re: [noparse][[/noparse]basicstamps] 555 Timer
>Date: Thu, 15 Jul 2004 20:37:53 -0700
>
>At 02:46 PM 7/15/2004, you wrote:
>
> >Does anyone know if it's possible to have the 555 delay for 55
> >minutes in a monostable configuation with no additional IC's?
>
>Sure, with a CMOS 555 and top quality R/C parts, time delays
>of several hours are easily possible with a 555. BTDT decades ago...
>You need GOOD quality low leakage caps and the highest value
>timing resistor your 555 will allow.
>
>The problem isn't delay time... it's stability. Especially over
>temperature.... the leakage of the large capacitor is likely to
>vary quite a bit with temperature, and make your timing drift
>all over.
>If you can operate in a temperature controlled environment you'll
>have a *big *advantage.
>If you really need to hit 55 minutes ACCURATELY and
>CONSISTENTLY, a 555 isn't the way. If you need approximately
>55 minutes, and 52 or 61 would be acceptable, with an average
>of 55 minutes then that's easily doable... Again, top quality R/C parts
>are the key... you ain't gonna get 1% accuracy with 10% tolerance
>parts... especially over any kind of temperature variation....
>
>Did you know the 555 was first introduced in 1971?
>The little sucker has been in production for 33 years now. Amazing!
>
>Steve D. - 555 user since 1974...
>
>
>[noparse][[/noparse]Non-text portions of this message have been removed]
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
>Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
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