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'[EE] Comments on circuit'
2005\05\15@144354 by Ake Hedman

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I need some advice comments on this circuit http://www.vscp.org/images/barometer001.gif  You probably laugh your guts out but but when you finished laughing please tell me what I have done wrong.

My thought is to build an input stage for the Freescale MPX4115 pressure sensor. This sensor outputs 0.2V - 4.8V for the pressure range 15 - 15kPa.

What I want to accomplish is:

- Something that can be calibrated with just software.
- That works over many pressure ranges not just barometer pressure ranges.
- Better than 0.1kPa resolution.

If I connected the sensor directly to the A/D input I would get 0.13kPa resolution. (5/1023) /(4.8/115) = 0.117 kPa/bit.

By amplifying the signal by 10 I can get  0.012  kPa/bit but I then need to shift it down to be able to read it with the A/D.

So I set up a difference amplifier with a gain of 10 and feed the sensor output to the (-) and a 100 kHz PWM signal through a LPF to the(-) getting (sensor - Vpwm) at the A/D input.

For the LPF I have set the corner frequency to about 16kHz. Don't actually know how to do this for PWM but my thinking has been that the choose values filter the PWM frequency away leaving the DC component. (How is the correct thinking?)

Is this a solution that is worth trying?  I can take away any static error during calibration but is there any sources for temperature or other dynamic errors that I need to take care of.

Comments appreciated (when you stopped laughing.. ;-) )

/Ake

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\15@151919 by Spehro Pefhany

picon face
At 08:43 PM 5/15/2005 +0200, you wrote:
>I need some advice comments on this circuit
>http://www.vscp.org/images/barometer001.gif  You probably laugh your guts
>out but but when you finished laughing please tell me what I have done wrong.

First off, you've got the + and - inputs swapped. When
that's fixed, the gain will not be 10, but approximately
100/11.8 = 8.47. The PIC output buffer will enter into it a bit.
If you don't like that, put a unity-gain op-amp buffer after the RC.
(with a dual op-amp, it's doesn't add any components).
Better yet make it a two or three pole filter with a time constant
in the tenths of a second. A single pole filter can only do so much.
Eg. if you use 100K and 1uF and PWM at 16kHz, then in one half-cycle
(31usec) the voltage will change by about t* (2.5/100K)*1/C = 0.7mV
at midscale, representing 7mV at the output or about 1.5 counts on a 10-bit
ADc.
The ripple with your setup will be outside the range of my linear
approximation, many many counts.

There's nothing inherently wrong with your concept, however just using a
12-bit ADC would be much better for most purposes.


>Is this a solution that is worth trying?  I can take away any static error
>during calibration but is there any sources for temperature or other
>dynamic errors that I need to take care of.

If the pressure transducer is ratiometric from the supply, then the PWM
is not a bad way of subtracting from that. You'll have to consider
the sensor accuracy itself. If you use a decent op-amp with low offset
voltage and decent resistors, they should not contribute substantially to
the drift.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\05\15@153632 by Harold Hallikainen

face picon face
Seems complicated to me! I'd be concerned about the stability of the
differential amplifier (if you're trying to build the diff amp yourself),
stability of the PWM output, ripple of the PWM output, etc. IF the
transducer indeed has the resolution and accuracy you're seeking, it seems
a simpler approach is to use an external A/D that has more resolution. I
did a precision thermometer using a Data Acquisition System chip from
Maxim. It, as I recall, has a 16 bit delta sigma A/D, a 10 bit D/A, and a
real time clock. Simple to interface to the PIC with SPI.

Harold
--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\05\15@154706 by Kenneth Lumia

picon face
Interesting idea.

The MPX sensor output has a large amount of noise.  You
will need to filter it extensively before applying it to your circuitry.
I seem to recall the app notes specifying a 750 Hz or so low
pass filter.  You will probably want an even lower cutoff frequency
than suggested.  A single pole RC is probably not sufficient for what
you are after - a multiple pole op-amp filter may be better.
Similarly, the PWM will probably need more filtering as well.
Extremely clean power to the circuit is a must.  Also, choose your
sampling frequency carefully to avoid harmonics.  Watch out for
non-linear regions of the op-amp near ground and 5V rails.
Finally, once you've treated it as best as is reasonable in
hardware, remember that software filtering is your friend.

> Is this a solution that is worth trying?  I can take away any static error
> during calibration but is there any sources for temperature or other
> dynamic errors that I need to take care of.

I'd try it, with additional filtering of course.  Temperature will
effect the results, you will need to determine the temperature
range and the accuracy required over that range to see if you
exceed the expected results (a rather complicated calculation,
considering all the "analog" parts and their tolerances).

.....klumiaKILLspamspam@spam@adelphia.net

{Original Message removed}

2005\05\15@154851 by Dave Tweed

face
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Ake Hedman <akhespamKILLspameurosource.se> wrote:
> I need some advice comments on this circuit
> http://www.vscp.org/images/barometer001.gif  You probably laugh your
> guts out but but when you finished laughing please tell me what I have
> done wrong.

You have the inputs to the opamp swapped. Another way of saying this
is that R4 needs to be the one connected to the opamp output and R3
needs to be grounded. And also R2 needs to be 10K, not 100K.

-- Dave Tweed

2005\05\15@161321 by Bob Ammerman

picon face
Anybody have any idea how accurate a sigma-delta A/D you can build using the
comparator in the PIC?

Bob Ammerman
RAm Systems

{Original Message removed}

2005\05\15@171011 by Ake Hedman

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Spehro,

First of all thanks for noticing  the +/. swap. Had it on paper and the component in eagle was the other way.  Probably should have taken me several hours to find on a board... ;-(

When you say adding a 2nd pole filter do you mean to replace the PWM LPF?  My thought was to also remove ripple in software. In this case it has known properties so this should be possible.

Where does the 11.8 come from in 100/11.8?

Thanks your help/suggestions are very much appreciated.

/Ake

Spehro Pefhany wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\15@171319 by Ake Hedman

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face
Harold,

I was trying to keep away from 12-bit A/D's due to cost reason. I have the uP and it have a 10-bit A/D. If there are any 12-bit A/D's available at a good price oh well its another situation. Suggestions?

/Ake

Harold Hallikainen wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\15@171537 by Ake Hedman

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face
Dave,

thanks. Probably wont have noticed myself. Saved hours of my time.

/Ake

Dave Tweed wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\15@173123 by Ake Hedman

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Kenneth,

Thanks for many *very* good suggestions.

In  one of there appnotes (http://www.freescale.com/files/sensors/doc/app_note/AN1646.pdf ) Freescale recommends a single pole filter with a cut off frequency of 650Hz and then use software.  At the same time they say that the noise is mostly white noise. Does a LPF realy help to get rid of white noice. I mean you remove the high frequency parts but still have the lower frequency noise left.

/Ake

Kenneth Lumia wrote:

{Quote hidden}

> {Original Message removed}

2005\05\15@173913 by Spehro Pefhany

picon face
At 11:10 PM 5/15/2005 +0200, you wrote:
>Spehro,
>
>First of all thanks for noticing  the +/. swap. Had it on paper and the
>component in eagle was the other way.  Probably should have taken me
>several hours to find on a board... ;-(
>
>When you say adding a 2nd pole filter do you mean to replace the PWM
>LPF?  My thought was to also remove ripple in software. In this case it
>has known properties so this should be possible.

If it's large you can run into nonlinearities when you don't expect to.

>Where does the 11.8 come from in 100/11.8?

In the DC path, the 1.8K is in series with the 10K (think of the capacitor
as being open circuit for DC). If you put a buffer in there,
as I suggested, it will reduce that to zero and eliminate the effect of the
PIC port output impedance.

That's the gain looking from a fictional DC PWM source. The gain from the
sensor will be half of (that number plus 1) because of the  voltage divider
on the non-inverting input.


Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffKILLspamspaminterlog.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


2005\05\15@180319 by Ake Hedman

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face
OK, makes sense.

Thanks
/Ake

Spehro Pefhany wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\15@182459 by olin_piclist

face picon face
Ake Hedman wrote:
> I need some advice comments on this circuit
> http://www.vscp.org/images/barometer001.gif

Hmm, where to begin.  I admit I didn't read all of your post (a bit long) so
maybe some of this is explained or addresed there.  However, several things
look seriously wrong if this is supposed to do what I think you intended.

1  -  This circuit performs thresholding with hystersis, which is contrary
to feeding the output into an A/D input.  You probably have the opamp inputs
backwards.

2  -  If this is supposed to be a linear amplifier and the opamp inputs are
flipped, then why attenuate the input?  R2 and R4 divide the input voltage
by 2, which doesn't make sense if you ultimately want to amplify it.

3  -  The R5 and C1 PWM filter has a rolloff frequency of about 900Hz.  The
PWM frequency needs to be well above that to filter out the individual PWM
pulses.  You need the residual PWM noise to be about 1/2 LSB on the A/D or
less, and I doubt this filter will do that for reasonable PWM frequencies.
You probably want a two pole filter at least.

4  -  If this is supposed to be a diff amp with the PWM setting the "0"
level, then R1 is definitely wrong.  Since the PWM filter output impedence
will vary with frequency and will be impossible to adjust for, it should be
buffered.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\15@183301 by olin_piclist

face picon face
Ake Hedman wrote:
> First of all thanks for noticing  the +/. swap. Had it on paper and the
> component in eagle was the other way.

If you are using Eagle you have another problem.  The lack of a dot at the
opamp output shows that it is not really connected to the wires.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\15@183524 by olin_piclist

face picon face
Ake Hedman wrote:
> My thought was to also remove ripple in software.

While theoretically possible, I think this is going to be very difficult and
result in significant errors in practise.  The A/D sampling would have to be
precisely timed with the PWM period to get consistant results, but then you
wouldn't know what those results meant because there would be a net sampling
bias on the PWM signal.  Use 2 or 3 poles of low pass filter and an opamp
buffer.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\15@183824 by olin_piclist

face picon face
Ake Hedman wrote:
> I was trying to keep away from 12-bit A/D's due to cost reason.

There is no need for this.  The 30F3013 is nicely priced and comes with 12
bit A/Ds.  Designing the circuit so that all errors amount to less than 1
part in 8000 is the tricky part.  At that level you have to consider offset
voltages caused by currents thru ground paths and a bunch of other stuff.
This is certainly doable, but not something a newbie is likely to get right
the first time.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\15@195656 by Anthony Van Herrewege

picon face
> Olin Lathrop <RemoveMEolin_piclistTakeThisOuTspamembedinc.com> wrote:
>
> If you are using Eagle you have another problem. The lack of a dot at the opamp output
> shows that it is not really connected to the wires.

Hm, that's not true. I do everything in Eagle and it doesn't place dots unless you're connecting 2 wires together (which isn't the same as connecting a wire to a pin).

Anthony


Website: http://members.lycos.nl/anthonyvh

               
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2005\05\15@221909 by Harold Hallikainen

face picon face
The Maxim part (16 bit data acquisition system) was not too bad, as I
recall. In the thermometer circuit (which uses a precision thermistor), I
use a 0.1% pull-up on the thermistor, then go directly into the A/D. The
top of the pull-up is the on-chip reference, so reference errors cancel.
This one part eliminated the need for differential amplifiers and a bunch
of precision parts. You connect it - it works. I often say "The ideal
design has zero parts." If you can get one part to do the work of 10, I
use the one. It may appear cheaper to use the 10 cheap parts, but the
hassles in getting it to work reliably, deal with adjustments, etc. is
just not worth it to me. I ended up with a circuit with no adjustments. It
just works...

Harold
"The ideal design has zero parts."


> Harold,
>
> I was trying to keep away from 12-bit A/D's due to cost reason. I have
> the uP and it have a 10-bit A/D. If there are any 12-bit A/D's available
> at a good price oh well its another situation. Suggestions?
>
> /Ake



--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\05\16@022712 by Ake Hedman

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face
It's just a sketch so I didn't put to much efforts into such things.

/Ake

Olin Lathrop wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@023555 by Ake Hedman

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face
Olin,

The buffering has been the general feedback from everyone which has been great.  And yes I swapped the inputs when I transfered the circuit from paper to eagle.

One of my questions was" how to think" when constructing the PWM LPF. Is it right to think that one just should remove the AC component. So if you say 1/2 bit on the A/D input I should filter for one tenth of that (having a gain of 10 ) in the difference stage?

Thanks for commenting. Appreciated.
/Ake

Olin Lathrop wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@024924 by Ake Hedman

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face
Olin,

that was a good suggestion. I need CAN also so the dsPIC30F3014 which also have 12-bit A/D's could be a good choice the price is good to.  Contrary to you I seldom get anything right the first time so that would not be a new  thing to me. ;-)

/Ake

Olin Lathrop wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@030023 by Ake Hedman

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face
Harold,

Agree completely with you on keeping parts down. KISS should be printed in the forehead of every engineers.  I forgot to look at the dsPic's which have 12-bit A/D's (dsPIC30F3014) and is at almost the same price as the 18F258 which was my original choice.  This is probably the way to go. However I got so interested in this circuit now and can learn a lot from it so I have to test it also I think. :-)

Thanks!
/Ake

Harold Hallikainen wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@065839 by Russell McMahon

face
flavicon
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> Anybody have any idea how accurate a sigma-delta A/D you can build
> using the comparator in the PIC?

AFAIR Scott Datallo achieved about 12 bits (or was that 10?) using PIC
pins alone, without using a comparator. So you should be able to do
substantially better using a "real" comparator. With a comparator I
think the main issue would be offset so you should be able to achieve
extremely good resolution with an SD converter - I'd guess 16-20 bit
range.


       RM

2005\05\16@103714 by Scott Dattalo

face
flavicon
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>> Anybody have any idea how accurate a sigma-delta A/D you can build
>> using the comparator in the PIC?
>
> AFAIR Scott Datallo achieved about 12 bits (or was that 10?) using PIC
> pins alone, without using a comparator.

(it's two t's and one ell).

Yes, I could achieve about 12-bits using a two I/O pin method. With a
single I/O pin I could get about 8. I think it'd be possible to get even
more if you're really careful.

The comparator helps in a couple of ways. First, the analog signal you're
measuring gets to see a high input impedance. With the method I used
(which I learned from Walter Banks) the analog signal sees a relatively
low input impedance. Second, I suspect (but haven't verified) that being
able to control (or even eliminate) hysteresis will allow one to achieve
even higher accuracy.

Another problem with I/O pins is that their input threshold has low power
supply rejection. This is something easier to control with a comparator.
Also, I suspect that the PIC power consumption increases slightly when the
I/O pin is held a voltage close to the switching threshold.

Scott

2005\05\16@110217 by Mark Rages

face picon face
On 5/15/05, Kenneth Lumia <spamBeGoneklumiaspamBeGonespamadelphia.net> wrote:
{Quote hidden}

This seems a good application for an old fashioned dual-slope A-D
converter.  They can have pretty good resolution and they naturally
integrate the signal.

Has anyone built one with a PIC?

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\05\16@124143 by Harold Hallikainen

face picon face


>
> This seems a good application for an old fashioned dual-slope A-D
> converter.  They can have pretty good resolution and they naturally
> integrate the signal.
>
> Has anyone built one with a PIC?
>


A PIC based dual slope A/D was used in the precision thermometer I just
redesigned. That design was maybe 10 years old. It used a quad op-amp and
a fair number of other parts. I replaced all that with the Maxim DAS part
to get 16 bit A/D, 10 bit D/A (which I use to vary display brightness),
and a real time clock. My previous dual slope experience has been using
the MC14433 in a design about 30 years ago. Worked great! Also used the
Intersil 7109 in another project. That one was interesting in that the A/D
circuitry was floating. I passed the busy AND clock, busy, and polarity
back through opto couplers. The counter in a 6522 counted the busy AND
clock to get the conversion. That also worked nicely.

Harold



--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\05\16@151331 by Peter

picon face

On Sun, 15 May 2005, Ake Hedman wrote:

> I need some advice comments on this circuit
> http://www.vscp.org/images/barometer001.gif  You probably laugh your guts out
> but but when you finished laughing please tell me what I have done wrong.

I am not laughing but you should not try to build a Schmitt Trigger.
Your amp is wired as non-inverting amp for the reference (PWM) but the
feedback resistor feeds into the + input and turns the circuit into a
Schmitt Trigger.

To make this a differential amp with gain 10 move R3 from 3/6 to 2/6,
reduce R2 to 10k and delete R4. The amp amplifies both the sensor input
and the reference (from pwm) 10 times and also the *noise* and error
from the pwm. This circuit may take some work to get it going.

Peter

2005\05\16@164636 by olin_piclist

face picon face
Anthony Van Herrewege wrote:
> Hm, that's not true. I do everything in Eagle and it doesn't place
> dots unless you're connecting 2 wires together (which isn't the same
> as connecting a wire to a pin).

Yes, but as I remember it, the OP had a junction of two lines right at the
opamp output.  There should be a dot where two wires and a pin connect.  I
also remember seeing a slight offset.  The lines are probably not connected
because he wasn't using the right grid when drawing the schematic.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\16@165523 by olin_piclist

face picon face
Ake Hedman wrote:
> It's just a sketch so I didn't put to much efforts into such things.

Argh!  Neatness and attention to detail count.  If you don't care, why
should anyone else?  Next time you ask 2000 people for advice on a sloppily
drawn sketch, please say so.  That way I can avoid wasting any time on it up
front.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\16@170013 by Ake Hedman

flavicon
face
As I written before. No they where not connected.  The drawing  was just a sketch so I didn't bother  to try to fix that as I never suspected  this to be the *big*  problem with this flirts attempt. ;-)   And Anthony is right to. It is perfectly valid to draw things in eagle with the line command instead of the net command and things get connected without dots.  Just a matter of preference.

Cheers
/Ake


Olin Lathrop wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@170822 by Ake Hedman

flavicon
face
I'm feed up with  this now and will get of this list. Its to much of this shit!!! Thanks everyone for your help during the years.

Cheers
/Ake

Olin Lathrop wrote:

{Quote hidden}

--  ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergavägen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se      Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

2005\05\16@173405 by olin_piclist

face picon face
Ake Hedman wrote:
> so I didn't bother  to try to fix that as I never suspected
> this to be the *big*  problem with this flirts attempt.

This is one reason neatness counts.  You avoid wasting time down ratholes
that others latch on to but aren't important to you.

> It is perfectly valid to draw things in eagle with
> the line command instead of the net command and things get connected
> without dots.  Just a matter of preference.

I strongly disagree with this.  I guess it's possible to do this due to how
Eagle works, but I certainly would not call it "valid", or something to be
left to the whims of preference.  In this case there is a clear right and
wrong way, and using NET is the right way.


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(978) 742-9014, http://www.embedinc.com

2005\05\16@230855 by phil B

picon face
Completely uncalled for.  The diagram is neat enough
for people to understand.  Even you did.  Enough
people responded that it is obvious to me that it is
quite clear to others as well.  I find it hard to see
that the omission of a single dot is deserving of this
diatribe.  I'm glad you have high standards, I'm not
that you visit them on others.

This sort of thing is what makes people think twice
about asking for help here.  Civility is free, wonder
why it seems to be in short supply - maybe Maxim is
making it...

Phil


--- Olin Lathrop <RemoveMEolin_piclistspamTakeThisOuTembedinc.com> wrote:
{Quote hidden}

*****************************************************************
> Embed Inc, embedded system specialists in Littleton
> Massachusetts
> (978) 742-9014, http://www.embedinc.com
> --

2005\05\16@233613 by Shawn Mulligan

flavicon
face
We'll never have the opportunity to know how many excellent minds he has
driven away.

I control an engineering department and we make some pretty interesting
things, but I long ago decided to simply read and avoid the nastiness of
posting. When he's right he's right, but when he's wrong he's extremely
wrong. All that mind negated by personality.


403-701-1440 (cell)
403-291-2917 (main)
403-291-2904 (fax)
> {Original Message removed}

2005\05\17@020153 by Wouter van Ooijen

face picon face
> Completely uncalled for.  The diagram is neat enough
> for people to understand.  Even you did.  Enough
> people responded that it is obvious to me that it is
> quite clear to others as well.  I find it hard to see
> that the omission of a single dot is deserving of this
> diatribe.

It is clearly an Eagle circuit drawing. How about the possibility that
the OP would use this drawing (or a modified version) as starting point
for creating a PCB?

Wouter van Ooijen

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


2005\05\17@034850 by Michael Rigby-Jones

picon face


>-----Original Message-----
>From: piclist-bouncesEraseMEspam.....mit.edu [EraseMEpiclist-bouncesspammit.edu]
>Sent: 17 May 2005 04:36
>To: 'Microcontroller discussion list - Public.'
>Subject: RE: [EE] Comments on circuit
>
>
>We'll never have the opportunity to know how many excellent
>minds he has driven away.
>
>I control an engineering department and we make some pretty
>interesting things, but I long ago decided to simply read and
>avoid the nastiness of posting. When he's right he's right,
>but when he's wrong he's extremely wrong. All that mind
>negated by personality.

Please don't turn this into yet another slanging match. If you have a
problem with Olin then please sort it out off-list.

Mike

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2005\05\17@100343 by Shawn Mulligan

flavicon
face
Then direction would be in order.



{Quote hidden}

> -

2005\05\17@100512 by Shawn Mulligan

flavicon
face
Fair enough.



{Quote hidden}

> -

2005\05\17@132344 by Peter

picon face


On Mon, 16 May 2005, Ake Hedman wrote:

> I'm feed up with  this now and will get of this list. Its to much of this
> shit!!! Thanks everyone for your help during the years.

Please don't. You are responding to an impulse of intensity 1/2000 imho.

Peter

2005\05\17@133740 by David P Harris

picon face
Peter wrote:

>
>
> On Mon, 16 May 2005, Ake Hedman wrote:
>
>> I'm feed up with  this now and will get of this list. Its to much of
>> this shit!!! Thanks everyone for your help during the years.
>
>
> Please don't. You are responding to an impulse of intensity 1/2000 imho.
>
> Peter

Whoa!  Ake stick around!  I agree, with Peter.

David

2005\05\17@145929 by Peter

picon face


On Tue, 17 May 2005, Wouter van Ooijen wrote:

> It is clearly an Eagle circuit drawing. How about the possibility that
> the OP would use this drawing (or a modified version) as starting point
> for creating a PCB?

If he had intended to then he would have clicked Tools->ERC before
generating the board and found out that it's unconnected.

Peter

2005\05\17@152442 by olin_piclist

face picon face
Peter wrote:
> If he had intended to then he would have clicked Tools->ERC before
> generating the board and found out that it's unconnected.

That's not going to find an unconnected output unless that output is the
only thing driving the net with all the rest of the connections inputs.
However, that wasn't the case since the remaining connections were to
passive components if I remember right.

Also remember that this guy posted a schematic and specifically asked for
comments.  I pointed out the missing connection as one of several problems I
noticed.  If this had been a real schematic (and we didn't know it wasn't at
the time), this could well have turned into an incorrect board eventually.
It also pointed out a bad use, or at least a misconception of how to use
Eagle.  Again, he asked.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\17@165337 by Wouter van Ooijen

face picon face
> If he had intended to then he would have clicked Tools->ERC before
> generating the board and found out that it's unconnected.

Are you sure he would have done that? I seldom use ERC because it
generates too many non-errors.

Wouter van Ooijen

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


2005\05\18@135617 by Peter

picon face

On Tue, 17 May 2005, Wouter van Ooijen wrote:

>> If he had intended to then he would have clicked Tools->ERC before
>> generating the board and found out that it's unconnected.
>
> Are you sure he would have done that? I seldom use ERC because it
> generates too many non-errors.

It's there for a reason imho. It will catch unconnected components like
Ake had before you start making the board. Since my version has no
auto-place this can save a lot of time later.

Peter

2005\05\18@144044 by Wouter van Ooijen

face picon face
> It's there for a reason imho. It will catch unconnected
> components like
> Ake had before you start making the board. Since my version has no
> auto-place this can save a lot of time later.

But it also produces all kinds of noise, like 'vss connected to gnd' and
'only one pin on net'. As it is I do not find it usefull.

Wouter van Ooijen

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


2005\05\19@070449 by Gerhard Fiedler

picon face
Wouter van Ooijen wrote:

> But it also produces all kinds of noise, like 'vss connected to gnd' and
> 'only one pin on net'. As it is I do not find it usefull.

Can't you configure that? I'm not familiar with Eagle. There may be a
connection matrix where you can configure what types of connections cause
errors and warnings. And it may also depend on how you create your library
parts (that is, how you define your pins).

A simple connection matrix is still not very smart, and many errors will go
undetected, or you get a lot of false positives, or both. But possibly you
can tweak it a bit to make it worthwhile.

Gerhard

2005\05\19@093205 by olin_piclist

face picon face
Gerhard Fiedler wrote:
>> But it also produces all kinds of noise, like 'vss connected to gnd'
>> and 'only one pin on net'. As it is I do not find it usefull.
>
> Can't you configure that?

Not that I know of.

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\19@093753 by Dave VanHorn

flavicon
face
At 08:32 AM 5/19/2005, Olin Lathrop wrote:
>Gerhard Fiedler wrote:
>>>But it also produces all kinds of noise, like 'vss connected to gnd'
>>>and 'only one pin on net'. As it is I do not find it usefull.
>>
>>Can't you configure that?
>
>Not that I know of.

Good old dos orcad.. Totally configurable, and realtime DRC that
actually works.
12 years obsolete, and still going strong.

2005\05\19@100840 by alan smith

picon face
Dave...i moved away from that because I found some
board houses can't read the gerbers.  Have you had any
issues like that?

--- Dave VanHorn <spamBeGonedvanhornSTOPspamspamEraseMEdvanhorn.org> wrote:
{Quote hidden}

> --

2005\05\19@103921 by Dave VanHorn

flavicon
face
At 09:08 AM 5/19/2005, alan smith wrote:
>Dave...i moved away from that because I found some
>board houses can't read the gerbers.  Have you had any
>issues like that?

Only once, when I sent 2.74x files to a house, and tehy were
complaining about the custom apertures in my aperture file.

I've never defined a custom aperture, EVER.

I'm not sure they were at all competent.  I sent the gerbers
elsewhere, and had no problem.

I only bother with 2.74X.

2005\05\19@131459 by Peter

picon face

On Wed, 18 May 2005, Wouter van Ooijen wrote:

> Date: Wed, 18 May 2005 20:38:39 +0200
> From: Wouter van Ooijen <KILLspamwouterspamBeGonespamvoti.nl>
> Reply-To: Microcontroller discussion list - Public. <EraseMEpiclistspamEraseMEmit.edu>
> To: 'Microcontroller discussion list - Public.' <@spam@piclist@spam@spamspam_OUTmit.edu>
> Subject: RE: [EE] Comments on circuit
>
>> It's there for a reason imho. It will catch unconnected
>> components like
>> Ake had before you start making the board. Since my version has no
>> auto-place this can save a lot of time later.
>
> But it also produces all kinds of noise, like 'vss connected to gnd' and
> 'only one pin on net'. As it is I do not find it usefull.

I love that kind of noise. vss connected to gnd is a failure to rename
pins and/or nets suitably imho. I don't know about one pin on net.

Peter

2005\05\19@142638 by olin_piclist

face picon face
Peter wrote:
> I love that kind of noise. vss connected to gnd is a failure to rename
> pins and/or nets suitably imho.

Not really.  It only means that you have a supply and a power pin on the
same net that have different names.  This can happen easily, and should be
none of Eagle's business.

For example, it's quite reasonble to call a ground symbol GND, and the
negative supply pin of a PIC Vss.  However if you connect the two in Eagle,
you get that stupid warning the Vss is connected GND.  You get the same
problem if you connect a net called +5V to the PIC pin called Vdd.  Each one
is a reasonable name on its own.  Changing the net name to Vdd would be
losing information and name it according to only one of its uses.  Changing
the PIC pin name to +5V would be outright wrong since PICs can run at
various voltages.

The right answer is for Eagle to be less uppity.  This kind of nonsense
makes the ERC less useful than it could be.  As a result, I usually run it
just once before starting layout.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\05\19@144233 by Wouter van Ooijen

face picon face
> I love that kind of noise. vss connected to gnd is a failure
> to rename pins and/or nets suitably imho.

Why? Microchip calls its 0V pin Vss, other chips call it GND or
something else. Why should it be an error to connect the two? If I am
realy creative I might want to run two PICs on a -5/0/+5 supply, so one
chip's Vdd and the other chip's Vss would both connect to GND. If I want
to do that, who is that ERC check to complain?

> I don't know about one pin on net.

My 'standard' way to do PIC circuits is to connect all I/O pins to a
bus. This part is often copied from a previous circuit. Next I'll use
the nets from that bus as I need them. Often some will be left unused.
Again, my choice! This is a bit like a compiler complaining about unused
variables, which often arises because my code customized by some macros.


Wouter van Ooijen

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


2005\05\19@150424 by Dave Tweed

face
flavicon
face
olin_piclist@embedinc.com (Olin Lathrop) wrote:
> Peter wrote:
> > I love that kind of noise. vss connected to gnd is a failure to rename
> > pins and/or nets suitably imho.
>
> Not really.  It only means that you have a supply and a power pin on the
> same net that have different names.  This can happen easily, and should be
> none of Eagle's business.

[snip]

> The right answer is for Eagle to be less uppity.  This kind of nonsense
> makes the ERC less useful than it could be.  As a result, I usually run it
> just once before starting layout.

Indeed. The whole concept of a "power" pin type in the library editors of
most schematic capture packages is seriously flawed, usually in a way
similar to this. My solution has been to define power pins as ordinary
"input" pins in my libraries. This shuts up the ERC chatter, and allows me
to do unusual things when I need to, like switch the power to a particular
part through a transistor.

-- Dave Tweed

2005\05\19@150916 by peiserma

flavicon
face
piclist-bounces@mit.edu wrote:
> Peter wrote:
>> I love that kind of noise. vss connected to gnd is a failure to
>> rename pins and/or nets suitably imho.
>
> Not really.  It only means that you have a supply and a power pin on
> the same net that have different names.  This can happen easily, and
> should be none of Eagle's business.

Have to disagree on that one. I will agree that it's annoying if all
your grounds are common....

>
> For example, it's quite reasonble to call a ground symbol GND, and the
> negative supply pin of a PIC Vss.  

not in all cases, no. It is not at all uncommon or unusual to have
different "grounds" that are not common, or only common at one point.
One good example is separate analog/digital supplies.

I had one case where I required an isolated supply to interface
with a line-operated product. I certainly did not want the
line-equipment "ground" (or neutral, COM, EARTH, or any of the other
terms encountered) tied to the user-operated equipment "ground". In
this case, I would have been upset if my schematic program did not
warn me that I connected "GND" to "Vss"


-Phil Eisermann

2005\05\19@152020 by Gerhard Fiedler

picon face
Olin Lathrop wrote:

> Peter wrote:
>> I love that kind of noise. vss connected to gnd is a failure to rename
>> pins and/or nets suitably imho.
>
> Not really.  It only means that you have a supply and a power pin on the
> same net that have different names.  This can happen easily, and should be
> none of Eagle's business.

So maybe you get better results by making the power pins on the PIC inputs
instead of power pins? If you don't use the implicit power connections
between equal-named power pins (something from way back in the early logic
design days that rarely makes sense anymore), it often doesn't make any
sense to classify the power pins as power pins, and the DRC gives better
results by making them inputs.

Gerhard

2005\05\20@043713 by Alan B. Pearce

face picon face
>> But it also produces all kinds of noise, like 'vss connected to gnd'
>> and 'only one pin on net'. As it is I do not find it usefull.
>
>I love that kind of noise. vss connected to gnd is a failure to rename
>pins and/or nets suitably imho. I don't know about one pin on net.

here where I work the insistence is that the IC should be set up as the
manufacturer describes it and the supply pins are visible, and you
explicitly connect them to the required supply. Means nothing is
"autoconnected" to somewhere it should not be, and gets around all these
noise DRC notes. Part of the checking process is to go through every DRC
note and make sure that a warning is for something that will be OK, and
there should be no errors noted, only warnings.

2005\05\20@135923 by Peter

picon face


On Thu, 19 May 2005, Wouter van Ooijen wrote:

>> I love that kind of noise. vss connected to gnd is a failure
>> to rename pins and/or nets suitably imho.
>
> Why? Microchip calls its 0V pin Vss, other chips call it GND or
> something else. Why should it be an error to connect the two? If I am

It is not an error but the connection should be *explicit*. I.e. 0 ohm
resistor or pin renaming. It's just my opinion. One makes enough
mistakes even so.

Peter

2005\05\20@144521 by Wouter van Ooijen

face picon face
> It is not an error but the connection should be *explicit*.
> I.e. 0 ohm
> resistor or pin renaming. It's just my opinion. One makes enough
> mistakes even so.

IMHO connecting the pins with a net is explicit enough. The pin names
are in the library domain, a circuit can not change them AFAIK. If you
mean that the libraries suck in this aspect I agree.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
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