Decoupling capacitor advice
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Posts: 46,084
Hi,
I just built myself an altimeter using the BS2, a MAX187 ADC, a
MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
(very very similar to the one on Shaun's web page actually).
My question is this: the data I'm getting is very noisy. At the
moment I have no decoupling capacitors in the circuit. Would this
help? (I believe it will). My real question is what value to choose,
and where to put them. The datasheet for the MPX4115 recommends
different values than those recommended for the MAX187 (1.0+0.01uF
and 4.7+0.1uF respectively). So which should I be using? Surely not
all four, two for each IC?
I've also read (on this list) that they should go as close as
possible to the chip I'm trying to decouple. So do I put them next to
the MPX4115 or the MAX187? And how close is close? Is an inch close
enough?
When I get this working well, I'll put it up on a website. Its a
rocket altimeter, and hopefully soon will include an ADXL190
accelerometer (to measure vertical acceleration), one of Analog
Devices' two-axis accelerometers (to measure vibration in the other
two axes), temperature sensors and magnetic field sensors (to measure
the Earth's magnetic field).
Thanks alot, sorry for all the questions.
James.
I just built myself an altimeter using the BS2, a MAX187 ADC, a
MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
(very very similar to the one on Shaun's web page actually).
My question is this: the data I'm getting is very noisy. At the
moment I have no decoupling capacitors in the circuit. Would this
help? (I believe it will). My real question is what value to choose,
and where to put them. The datasheet for the MPX4115 recommends
different values than those recommended for the MAX187 (1.0+0.01uF
and 4.7+0.1uF respectively). So which should I be using? Surely not
all four, two for each IC?
I've also read (on this list) that they should go as close as
possible to the chip I'm trying to decouple. So do I put them next to
the MPX4115 or the MAX187? And how close is close? Is an inch close
enough?
When I get this working well, I'll put it up on a website. Its a
rocket altimeter, and hopefully soon will include an ADXL190
accelerometer (to measure vertical acceleration), one of Analog
Devices' two-axis accelerometers (to measure vibration in the other
two axes), temperature sensors and magnetic field sensors (to measure
the Earth's magnetic field).
Thanks alot, sorry for all the questions.
James.
Comments
from and that, ideally, would be the best place for the caps. Anything
short of this is a walk in the dark. My experience would tell me that
one inch is close enough. Where the power comes on to the board might
be a good place to start. The reason for two different sizes is that
one is narrow pulses and the other for wider pulses. Simple RC filter
with no R..
regards,
Leroy
129275@s... wrote:
>
> Hi,
> I just built myself an altimeter using the BS2, a MAX187 ADC, a
> MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
> (very very similar to the one on Shaun's web page actually).
> My question is this: the data I'm getting is very noisy. At the
> moment I have no decoupling capacitors in the circuit. Would this
> help? (I believe it will). My real question is what value to choose,
> and where to put them. The datasheet for the MPX4115 recommends
> different values than those recommended for the MAX187 (1.0+0.01uF
> and 4.7+0.1uF respectively). So which should I be using? Surely not
> all four, two for each IC?
> I've also read (on this list) that they should go as close as
> possible to the chip I'm trying to decouple. So do I put them next to
> the MPX4115 or the MAX187? And how close is close? Is an inch close
> enough?
> When I get this working well, I'll put it up on a website. Its a
> rocket altimeter, and hopefully soon will include an ADXL190
> accelerometer (to measure vertical acceleration), one of Analog
> Devices' two-axis accelerometers (to measure vibration in the other
> two axes), temperature sensors and magnetic field sensors (to measure
> the Earth's magnetic field).
> Thanks alot, sorry for all the questions.
> James.
>
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--
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
* Phone: (513) 697-7539 *
* Cell : (513) 300-8632 *
* Email: leroy@f... *
* Home page URL: http://home.fuse.net/leroy/ *
* Resume URL: http://home.fuse.net/leroy/resume.htm *
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
what type it is. I scope the power supplies of my projects looking
for noise and oscillations. What I have found it that a .1uF under
the power pins of every chip is a good place to start. More
capacitance would most likel;y be required if the regulator is on a
different board, or if the regulator is far away. Also, the DC ground
should be nice and hefty, there should be lots of it. Having seperate
DC and digital grounds is sometimes a good idea.
Regards
Rich
http://geocities.com/rbc1956
--- In basicstamps@y..., 129275@s... wrote:
>
> Hi,
> I just built myself an altimeter using the BS2, a MAX187 ADC, a
> MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
> (very very similar to the one on Shaun's web page actually).
> My question is this: the data I'm getting is very noisy. At the
> moment I have no decoupling capacitors in the circuit. Would this
> help? (I believe it will). My real question is what value to
choose,
> and where to put them. The datasheet for the MPX4115 recommends
> different values than those recommended for the MAX187 (1.0+0.01uF
> and 4.7+0.1uF respectively). So which should I be using? Surely not
> all four, two for each IC?
> I've also read (on this list) that they should go as close as
> possible to the chip I'm trying to decouple. So do I put them next
to
> the MPX4115 or the MAX187? And how close is close? Is an inch close
> enough?
> When I get this working well, I'll put it up on a website. Its a
> rocket altimeter, and hopefully soon will include an ADXL190
> accelerometer (to measure vertical acceleration), one of Analog
> Devices' two-axis accelerometers (to measure vibration in the other
> two axes), temperature sensors and magnetic field sensors (to
measure
> the Earth's magnetic field).
> Thanks alot, sorry for all the questions.
> James.
sure if I try I could find one somewhere and borrow that.
James.
--- In basicstamps@y..., iceninevt@y... wrote:
> I agree that a scope is necessary to see where the noise is, and of
> what type it is. I scope the power supplies of my projects looking
> for noise and oscillations. What I have found it that a .1uF under
> the power pins of every chip is a good place to start. More
> capacitance would most likel;y be required if the regulator is on a
> different board, or if the regulator is far away. Also, the DC
ground
> should be nice and hefty, there should be lots of it. Having
seperate
> DC and digital grounds is sometimes a good idea.
>
> Regards
>
> Rich
>
> http://geocities.com/rbc1956
>
> --- In basicstamps@y..., 129275@s... wrote:
> >
> > Hi,
> > I just built myself an altimeter using the BS2, a MAX187 ADC, a
> > MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
> > (very very similar to the one on Shaun's web page actually).
> > My question is this: the data I'm getting is very noisy. At the
> > moment I have no decoupling capacitors in the circuit. Would this
> > help? (I believe it will). My real question is what value to
> choose,
> > and where to put them. The datasheet for the MPX4115 recommends
> > different values than those recommended for the MAX187
(1.0+0.01uF
> > and 4.7+0.1uF respectively). So which should I be using? Surely
not
> > all four, two for each IC?
> > I've also read (on this list) that they should go as close as
> > possible to the chip I'm trying to decouple. So do I put them
next
> to
> > the MPX4115 or the MAX187? And how close is close? Is an inch
close
> > enough?
> > When I get this working well, I'll put it up on a website. Its a
> > rocket altimeter, and hopefully soon will include an ADXL190
> > accelerometer (to measure vertical acceleration), one of Analog
> > Devices' two-axis accelerometers (to measure vibration in the
other
> > two axes), temperature sensors and magnetic field sensors (to
> measure
> > the Earth's magnetic field).
> > Thanks alot, sorry for all the questions.
> > James.
noise by decoupling, filtering and other methods. If it's still an issue
when you read this, let me know, and I'll drag the link out of my Favorites
into here.
Also, If decoupling isn't the issue here, I wouldn't be surprised. Your ADC
may actually be capturing exactly what the sensor is outputting, and it may
be very non-linear (as are many fast sensors - they are actually too fast at
times.)I've found that many types of sensors throw oddball values that we
might consider noise, which in a faster process would be less significant.
If these odd values are being output just as the stamp is reading the input,
it makes the result much worse that reality. You may want to start by
averaging the inputs and setting a range with high and low limits as a
simple filter. There was a nice thread on this list a couple of months ago
that contained some methods, from simple to complex, that really work. I
believe Tracy was the expert in this area.
If the decoupling works, sorry - sometimes I just like to hear myself talk
(or type) and I'll be glad you found a simple solution.
Chris
>
Original Message
> From: 129275@s... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=K0hEVYh6-j1E6cNvgQerk28vFgofZAsCMoBzmwl_aJSOfLeJjaH2UGu8juT237iK034bXC0nWR8cuR0MGQ]129275@s...[/url
> Sent: Tuesday, June 26, 2001 9:42 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Decoupling capacitor advice
>
>
>
> Ok, thanks for the ideas. I don't have a scope unfortunately, but I'm
> sure if I try I could find one somewhere and borrow that.
> James.
>
> --- In basicstamps@y..., iceninevt@y... wrote:
> > I agree that a scope is necessary to see where the noise is, and of
> > what type it is. I scope the power supplies of my projects looking
> > for noise and oscillations. What I have found it that a .1uF under
> > the power pins of every chip is a good place to start. More
> > capacitance would most likel;y be required if the regulator is on a
> > different board, or if the regulator is far away. Also, the DC
> ground
> > should be nice and hefty, there should be lots of it. Having
> seperate
> > DC and digital grounds is sometimes a good idea.
> >
> > Regards
> >
> > Rich
> >
> > http://geocities.com/rbc1956
> >
> > --- In basicstamps@y..., 129275@s... wrote:
> > >
> > > Hi,
> > > I just built myself an altimeter using the BS2, a MAX187 ADC, a
> > > MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
> > > (very very similar to the one on Shaun's web page actually).
> > > My question is this: the data I'm getting is very noisy. At the
> > > moment I have no decoupling capacitors in the circuit. Would this
> > > help? (I believe it will). My real question is what value to
> > choose,
> > > and where to put them. The datasheet for the MPX4115 recommends
> > > different values than those recommended for the MAX187
> (1.0+0.01uF
> > > and 4.7+0.1uF respectively). So which should I be using? Surely
> not
> > > all four, two for each IC?
> > > I've also read (on this list) that they should go as close as
> > > possible to the chip I'm trying to decouple. So do I put them
> next
> > to
> > > the MPX4115 or the MAX187? And how close is close? Is an inch
> close
> > > enough?
> > > When I get this working well, I'll put it up on a website. Its a
> > > rocket altimeter, and hopefully soon will include an ADXL190
> > > accelerometer (to measure vertical acceleration), one of Analog
> > > Devices' two-axis accelerometers (to measure vibration in the
> other
> > > two axes), temperature sensors and magnetic field sensors (to
> > measure
> > > the Earth's magnetic field).
> > > Thanks alot, sorry for all the questions.
> > > James.
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed with. Text
> in the Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
wrote:
> There are a couple of super websites full of excellent advice on
managing
> noise by decoupling, filtering and other methods. If it's still an
issue
> when you read this, let me know, and I'll drag the link out of my
Favorites
> into here.
Yes please, if you could let me have those links I'd appreciate it.
> Also, If decoupling isn't the issue here, I wouldn't be surprised.
Your ADC
> may actually be capturing exactly what the sensor is outputting,
and it may
> be very non-linear (as are many fast sensors - they are actually
too fast at
> times.)I've found that many types of sensors throw oddball values
that we
> might consider noise, which in a faster process would be less
significant.
> If these odd values are being output just as the stamp is reading
the input,
> it makes the result much worse that reality. You may want to start
by
> averaging the inputs and setting a range with high and low limits
as a
> simple filter. There was a nice thread on this list a couple of
months ago
> that contained some methods, from simple to complex, that really
work. I
> believe Tracy was the expert in this area.
>
> If the decoupling works, sorry - sometimes I just like to hear
myself talk
> (or type) and I'll be glad you found a simple solution.
I won't have a chance to try it until probably the beginning of next
week (kind of busy this week, and the weekend is booked up too). But
yes, a software solution by averaging inputs was something else I was
considering.
Thanks alot, James.
line noise.
I deal with pressure sensors quite often and one thing most people
don't realize is that sound is a pressure wave. I get involved in
fractions of an inch of water full scale (27.72 inches is close to 1
psi)
The noise might be sound. I would agree to check the scope to see
the frequency. Airplanes use a static pitot tube for velocity. In
HVAC, we use ultra low pressure transmitters, and usually integrate
the heck out of them to kill the noise. Don't forget wind noise is a
possibility, as well as vibration of the sensor itself.
With your range in the PSIG, you might not see as large a problem,
but it might be beneficial to test your sensor by playing the stereo,
holding it out the car window at 90 mph, or singing to it.
I don't recommend breaking any laws, so tell your wife you need to go
to Germany and drive the Autobahn : ) and to Japan to sing Karaoke,
and invite the neighbors for a party : )
Dave
--- In basicstamps@y..., 129275@s... wrote:
>
> Hi,
> I just built myself an altimeter using the BS2, a MAX187 ADC, a
> MPX4115 pressure sensor and a 25LC640 EEPROM for storing the data
> (very very similar to the one on Shaun's web page actually).
> My question is this: the data I'm getting is very noisy. At the
> moment I have no decoupling capacitors in the circuit. Would this
> help? (I believe it will). My real question is what value to
choose,
> and where to put them. The datasheet for the MPX4115 recommends
> different values than those recommended for the MAX187 (1.0+0.01uF
> and 4.7+0.1uF respectively). So which should I be using? Surely not
> all four, two for each IC?
> I've also read (on this list) that they should go as close as
> possible to the chip I'm trying to decouple. So do I put them next
to
> the MPX4115 or the MAX187? And how close is close? Is an inch close
> enough?
> When I get this working well, I'll put it up on a website. Its a
> rocket altimeter, and hopefully soon will include an ADXL190
> accelerometer (to measure vertical acceleration), one of Analog
> Devices' two-axis accelerometers (to measure vibration in the other
> two axes), temperature sensors and magnetic field sensors (to
measure
> the Earth's magnetic field).
> Thanks alot, sorry for all the questions.
> James.
http://www.williamson-labs.com/480_byp.htm
http://www.ednmag.com/ednmag/reg/1995/090195/18df5.htm
I noted a later posting about lead length, etc....
I try to stick to a 1mm rule for the + lead to the Vcc pin and I double the
trace width of Vss. Especially with very busy chips, such as a binary
counter, where there are always many gates switching I often find a need to
use some combination of .01, .1, and 1 uF caps, at times, all three.
BTW, how is Swansea this time of year? I'm on an ISO committee that met at
the University there last year in the fall - during your petrol "crisis".
Somehow, the people were all very friendly despite the pressure of the day.
And, how did The Mumbles ever get it's name? Why not Thomasville, or
something?
Chris
>
Original Message
> From: 129275@s... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Ckq_iVrhjA2Vs4MByiEWfFcxMO4F5hImFp2ExbkYzzMofol4SmgFaq8CItuJQVHzgDqxhIfkAus3s0WMzR0]129275@s...[/url
> Sent: Tuesday, June 26, 2001 11:43 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Decoupling capacitor advice
>
>
> --- In basicstamps@y..., "Chris Loiacono (E-mail)" <chris01@t...>
> wrote:
> > There are a couple of super websites full of excellent advice on
> managing
> > noise by decoupling, filtering and other methods. If it's still an
> issue
> > when you read this, let me know, and I'll drag the link out of my
> Favorites
> > into here.
>
> Yes please, if you could let me have those links I'd appreciate it.
>
>
>
wrote:
> Decoupling links, as promised:
>
> http://www.williamson-labs.com/480_byp.htm
>
> http://www.ednmag.com/ednmag/reg/1995/090195/18df5.htm
Thanks for those, they look quite interesting, though I haven't had
chance to read them properly yet.
> BTW, how is Swansea this time of year? I'm on an ISO committee that
met at
> the University there last year in the fall - during your
petrol "crisis".
> Somehow, the people were all very friendly despite the pressure of
the day.
> And, how did The Mumbles ever get it's name? Why not Thomasville, or
> something?
Swansea is great this time of year. Weather is good, warm (but not
hot), dry, sunny. Unfortunately the rest of the year it can be fairly
crappy (grey, wet, windy). Great place to be at University though,
what with the beach right there, and the Gower peninsula a few miles
away. And I've no idea how The Mumbles got its name.
James.