Half power rail reference...

[Martin Brown]

On 05/11/2020 08:40, Rickster C wrote:

On Thursday, November 5, 2020 at 2:37:38 AM UTC-5, Jeroen Belleman
wrote:
On 2020-11-05 02:16, Rickster C wrote:

Not sure how I would determine how to apply feedback. What would
be the measurement to use to set the feedback? I don\'t have a
way to measure the voltage. That\'s the point, to provide a
reference voltage at Vcc/2 without active monitoring or
control.[...]

You wanted this to provide a reference??? Sorry, I assumed you
wanted a power rail splitter.

Forget it then. You need a simple resistor divider, maybe buffered
with a unit gain amp.

+1

The resistor divider has tolerance related error while the 50/50
thing powered from the same supply as the signal source canceling
variations has rather near zero error. Advice is fine, but I was
asking if anyone remembered the thread where it was already discussed
in detail.

I am mystified why you need this centre reference voltage to be so
exactly half way between the two supply rails. Linear opamps work fine
with a slightly asymmetric power supply provided that they don\'t clip.

You just have to make sure that everything is measured consistently
relative to the right signal earth reference.

An instrumentation amplifier on the front end helps in extreme cases but
it sounds like your sensor has already conditioned the signals somewhat.

You might want to consider a higher order low pass analogue filter in
front of the ADC to attenuate any electrical noise that may be present
from long probe leads and fluorescent lighting in the environment.

There must be someone who was involved in the thread who remembers
the subject line.

Search on Google groups if you can remember any keywords or authors.

--
Regards,
Martin Brown

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...

On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer
wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the output
value
is a fraction of the sensor supply. Vref at Diff + input is half supply
voltage. This may not be of value though. I\'m pretty tired and I have
a
hundred other things I\'m looking at. I don\'t think I work this hard
when I
get paid to do this stuff. But at least I get to do it on my own
without
having to get consensus from a dozen other people some of who don\'t even
do
hardware.

3.3V |
--- |
| |
+----| Vcco
|
+----| Sq Wave
| |
\\ |
Rb-C1 TC ~10 ms Rb / |
\\ |
/ |
Gnd C1 | |
|---||---+----| +
Vref |
+--\\/\\/-+ Gnd C2 |
5V | | |---||---+ |Diff In
Sensor +--|\\ | | |
|\\ | >--+---/\\/\\/----+----| -
| >--\\/\\/-+--|/ Ra | |
|/ | \\ |
\\ Ra / |
/ \\ |
\\ / |
/ | |
| +----| D-S Out
--- |
Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC circuit I\'d
avoid
square waves unless there was some good reason why they couldn\'t be
avoided.
Noise generated by fast transitions can easily end up in unexpected
places.

I\'d be more likely to have a look here if an external reference was
needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch

Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

Do you see the circuit?

No I\'m blind and unable to print with a monospace font.

Your schematic is a good start but if you want advice then please spend some
time improving it.

In your position I\'d want to know the following in addition to the schematic
you\'ve already posted.

1. More information about the sensor characteristics is needed. How it
connected to the board and by how long a cable? Is the cable shielded? What
kind of cable is it? Is the grounding common? What is the source impedance?

2. What are the component values for the op-amp circuit and show the + and -
inputs. It does not matter if the values are not yet finalised. What power
rails is the op-amp using? What is the part number of the op-amp?

3. Is any protection needed for matters such as ESD or someone connecting
the wrong sensor? Is there any risk of the sensor input going outside the
range 0 to 5V? Perhaps if a fault occurs in the senssor?

4. Is filtering required above 100Hz? See Martin Brown\'s excellent advice.

5. Is that an individual DAC (Part number?) or part of a chip with multiple
DACs (Part number?)

Expect more questions when the above is taken care of.
Also expect advice from people who read this group who can trivially show
you how to design the best signal conditioning circuitry for this
application, but only if they have a clear picture of what you need.
This doesn\'t mean they will just give you the complete design, but you might
learn something.

If you have different sensors with very different characteristics then one
schematic per sensor may be needed.

At this stage I\'d be using a hand drawn schematic but ASCII art is ok.

Enjoy your ice cream.

Oh, you are asking about D-S out, so I guess not. Searching I see I didn\'t
mention this is a sigma-delta ADC input. As I said, I\'m very tired at the
moment.

Are you familiar with those? You should also note that I mentioned the
bandwidth of the signal can be limited to 100 Hz with no ill effects which
the capacitors should accomplish just fine.

Heck, the O2 sensor has a 90% rise time of 5 seconds. We\'ll run a low
pass filter on the 200 Hz measurement to get lots of precision and low
noise. The pressure sensors are the sort of signal you see on hospital TV
shows.

I\'m off to have a bit of ice cream and bed. Tired am I.

--

Rick C.

 

[Rickster C]

On Thursday, November 5, 2020 at 5:19:29 AM UTC-5, piglet wrote:

On 04/11/2020 9:00 pm, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an idea for generating an accurate voltage at half the supply rail by switching an output at a 50/50 duty cycle to feed an RC. I can\'t seem to find that thread.. I\'m wondering what the limitations might be on the accuracy. Obviously the difference in drive capability is a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two edges within the digital device. That can be mitigated by using a slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality integrating capacitor might be important as well. Also ceramic caps can be microphonic, so film caps will be needed. In fact I need to specify that all through the sensor power supply.

You mean \"half voltage\".

Thanks, but trying that both with and without the quotes didn\'t turn up the thread going all the way back to December. It couldn\'t have been that long ago could it? Seems like maybe three for four months back.

I\'m not sure how bad it would be to simply use a pair of 0.1% resistors.. That would add error somewhere between 0.1% and 0.2% (not thinking about it too hard). There will be other sources of error from this same effect elsewhere (dividing the 5V signal source to 3.3 volts... or maybe not. Perhaps that can be mitigated by not using equal value resistors in the input and feedback paths.

It\'s funny that the other guys on the project don\'t seem to be able to think about this stuff. I guess they are mostly used to just plopping down chips. Heck, a new FPGA guy wanted to use a $20 Xilinx part instead of a $4-5 Gowin part!

I was happy to find I can get 10 nF C0G for under a nickle and 100 nF for around a dime. I thought they didn\'t come that large. They do get large!


If you don\'t think the 0.1% resistive divider is good enough can\'t you
calibrate it out during power-on self test? Or even add a analog switch
mux upstream for sensor sanity checking?

Please tell meh ow to calibrate absolute accuracy? I still don\'t follow why such a simple technique should not be used.

What does the mux do???

--

Rick C.

-+- Get 1,000 miles of free Supercharging
-+- Tesla referral code - https://ts.la/richard11209

 

[Rickster C]

On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer
wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the output
value
is a fraction of the sensor supply. Vref at Diff + input is half supply
voltage. This may not be of value though. I\'m pretty tired and I have
a
hundred other things I\'m looking at. I don\'t think I work this hard
when I
get paid to do this stuff. But at least I get to do it on my own
without
having to get consensus from a dozen other people some of who don\'t even
do
hardware.

3.3V |
--- |
| |
+----| Vcco
|
+----| Sq Wave
| |
\\ |
Rb-C1 TC ~10 ms Rb / |
\\ |
/ |
Gnd C1 | |
|---||---+----| +
Vref |
+--\\/\\/-+ Gnd C2 |
5V | | |---||---+ |Diff In
Sensor +--|\\ | | |
|\\ | >--+---/\\/\\/----+----| -
| >--\\/\\/-+--|/ Ra | |
|/ | \\ |
\\ Ra / |
/ \\ |
\\ / |
/ | |
| +----| D-S Out
--- |
Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC circuit I\'d
avoid
square waves unless there was some good reason why they couldn\'t be
avoided.
Noise generated by fast transitions can easily end up in unexpected
places.

I\'d be more likely to have a look here if an external reference was
needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch

Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

Do you see the circuit?

No I\'m blind and unable to print with a monospace font.

Your schematic is a good start but if you want advice then please spend some
time improving it.

In your position I\'d want to know the following in addition to the schematic
you\'ve already posted.

1. More information about the sensor characteristics is needed. How it
connected to the board and by how long a cable? Is the cable shielded? What
kind of cable is it? Is the grounding common? What is the source impedance?

2. What are the component values for the op-amp circuit and show the + and -
inputs. It does not matter if the values are not yet finalised. What power
rails is the op-amp using? What is the part number of the op-amp?

3. Is any protection needed for matters such as ESD or someone connecting
the wrong sensor? Is there any risk of the sensor input going outside the
range 0 to 5V? Perhaps if a fault occurs in the senssor?

4. Is filtering required above 100Hz? See Martin Brown\'s excellent advice.

5. Is that an individual DAC (Part number?) or part of a chip with multiple
DACs (Part number?)

Expect more questions when the above is taken care of.
Also expect advice from people who read this group who can trivially show
you how to design the best signal conditioning circuitry for this
application, but only if they have a clear picture of what you need.
This doesn\'t mean they will just give you the complete design, but you might
learn something.

If you have different sensors with very different characteristics then one
schematic per sensor may be needed.

At this stage I\'d be using a hand drawn schematic but ASCII art is ok.

Enjoy your ice cream.

Sorry, that is your initial misunderstanding. I am not asking for design advice. I am asking for someone who remembers the thread where this was discussed a few months back. I\'m not able to find it.

Rather than ask for fully documented design information, why don\'t you tell me what you are thinking and I can help you understand.

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...

On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying this
specific ventilator (if that\'s what it is) so that if I ever end up in a
hospital I can refuse to let them use it on me.

 

[Rickster C]

On Thursday, November 5, 2020 at 3:01:21 PM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying this
specific ventilator (if that\'s what it is) so that if I ever end up in a
hospital I can refuse to let them use it on me.

lol So do you have anything constructive to offer? I find it amazing that you need full specifications of everything in the design to talk about generating a half Vcc voltage using a 50/50 duty cycle digital output.

Whatever. \"Forget about it Jake, it\'s the Internet.\"

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:66d7fde9-3d00-4b80-ab36-5b46ab269a47o@googlegroups.com...

On Thursday, November 5, 2020 at 3:01:21 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5,
Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying this
specific ventilator (if that\'s what it is) so that if I ever end up in a
hospital I can refuse to let them use it on me.

lol So do you have anything constructive to offer?

I think enough has already been offered.

I find it amazing that you need full specifications of everything in the
design

I\'m not surprised because I haven\'t asked for \"full specifications of
everything in the design\" just a reasonable description of what you\'re
trying to achieve with your sensor to ADC circuit.

to talk about generating a half Vcc voltage using a 50/50 duty cycle
digital output.

No-one except you would generate an ADC reference voltage like that.
I\'m not saying it won\'t work, and if you\'re trying to reduce component cost
to an absolute minimum then it may help with that.
But it wouldn\'t be my first choice for an ADC reference voltage in a
hospital ventilator.

Whatever. \"Forget about it Jake, it\'s the Internet.\"

--

Rick C.

 

[Phil Hobbs]

On 11/5/20 2:43 PM, Rickster C wrote:

On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...


On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...


On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...


On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM
UTC-5, Robert Baer wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the
output value is a fraction of the sensor supply. Vref at
Diff + input is half supply voltage. This may not be of
value though. I\'m pretty tired and I have a hundred other
things I\'m looking at. I don\'t think I work this hard when
I get paid to do this stuff. But at least I get to do it on
my own without having to get consensus from a dozen other
people some of who don\'t even do hardware.

3.3V | --- | | | +----| Vcco | +----| Sq Wave | | \\
| Rb-C1 TC ~10 ms Rb / | \\ | / | Gnd C1 |
| |---||---+----| + Vref | +--\\/\\/-+ Gnd C2 | 5V
| | |---||---+ |Diff In Sensor +--|\\ |
| | |\\ | >--+---/\\/\\/----+----| - |
--\\/\\/-+--|/ Ra | | |/ |
\\ | \\ Ra / | / \\
| \\ / | / | | |
+----| D-S Out --- | Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC
circuit I\'d avoid square waves unless there was some good
reason why they couldn\'t be avoided. Noise generated by fast
transitions can easily end up in unexpected places.

I\'d be more likely to have a look here if an external reference
was needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch



Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

Do you see the circuit?

No I\'m blind and unable to print with a monospace font.

Your schematic is a good start but if you want advice then please
spend some time improving it.

In your position I\'d want to know the following in addition to the
schematic you\'ve already posted.

1. More information about the sensor characteristics is needed. How
it connected to the board and by how long a cable? Is the cable
shielded? What kind of cable is it? Is the grounding common? What
is the source impedance?

2. What are the component values for the op-amp circuit and show
the + and - inputs. It does not matter if the values are not yet
finalised. What power rails is the op-amp using? What is the part
number of the op-amp?

3. Is any protection needed for matters such as ESD or someone
connecting the wrong sensor? Is there any risk of the sensor input
going outside the range 0 to 5V? Perhaps if a fault occurs in the
senssor?

4. Is filtering required above 100Hz? See Martin Brown\'s excellent
advice.

5. Is that an individual DAC (Part number?) or part of a chip with
multiple DACs (Part number?)

Expect more questions when the above is taken care of. Also expect
advice from people who read this group who can trivially show you
how to design the best signal conditioning circuitry for this
application, but only if they have a clear picture of what you
need. This doesn\'t mean they will just give you the complete
design, but you might learn something.

If you have different sensors with very different characteristics
then one schematic per sensor may be needed.

At this stage I\'d be using a hand drawn schematic but ASCII art is
ok.

Enjoy your ice cream.

Sorry, that is your initial misunderstanding. I am not asking for
design advice. I am asking for someone who remembers the thread
where this was discussed a few months back. I\'m not able to find
it.

I searched GG with \"PWM DAC accuracy\", and the first thread that came up
was \"Attainable PWM accuracy?\" from a year ago.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Rickster C]

On Thursday, November 5, 2020 at 5:15:15 PM UTC-5, Phil Hobbs wrote:

On 11/5/20 2:43 PM, Rickster C wrote:
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...


On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...


On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...


On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM
UTC-5, Robert Baer wrote:
Rickster C wrote:

The 3.3V for Vcco is ratiod from the 5V sensor supply as the
output value is a fraction of the sensor supply. Vref at
Diff + input is half supply voltage. This may not be of
value though. I\'m pretty tired and I have a hundred other
things I\'m looking at. I don\'t think I work this hard when
I get paid to do this stuff. But at least I get to do it on
my own without having to get consensus from a dozen other
people some of who don\'t even do hardware.

3.3V | --- | | | +----| Vcco | +----| Sq Wave | | \\
| Rb-C1 TC ~10 ms Rb / | \\ | / | Gnd C1 |
| |---||---+----| + Vref | +--\\/\\/-+ Gnd C2 | 5V
| | |---||---+ |Diff In Sensor +--|\\ |
| | |\\ | >--+---/\\/\\/----+----| - |
--\\/\\/-+--|/ Ra | | |/ |
\\ | \\ Ra / | / \\
| \\ / | / | | |
+----| D-S Out --- | Gnd

Ok well if I wanted a 1.65V reference for a sensitive ADC
circuit I\'d avoid square waves unless there was some good
reason why they couldn\'t be avoided. Noise generated by fast
transitions can easily end up in unexpected places.

I\'d be more likely to have a look here if an external reference
was needed:
https://www.google.com/search?q=1.65V+precision+reference&tbm=isch



Assuming it wasn\'t sufficient to just use two resistors, or two resistors
and an op amp.

I\'m tired too and will be away for the next 24 hours.

What is D-S Out?

Do you see the circuit?

No I\'m blind and unable to print with a monospace font.

Your schematic is a good start but if you want advice then please
spend some time improving it.

In your position I\'d want to know the following in addition to the
schematic you\'ve already posted.

1. More information about the sensor characteristics is needed. How
it connected to the board and by how long a cable? Is the cable
shielded? What kind of cable is it? Is the grounding common? What
is the source impedance?

2. What are the component values for the op-amp circuit and show
the + and - inputs. It does not matter if the values are not yet
finalised. What power rails is the op-amp using? What is the part
number of the op-amp?

3. Is any protection needed for matters such as ESD or someone
connecting the wrong sensor? Is there any risk of the sensor input
going outside the range 0 to 5V? Perhaps if a fault occurs in the
senssor?

4. Is filtering required above 100Hz? See Martin Brown\'s excellent
advice.

5. Is that an individual DAC (Part number?) or part of a chip with
multiple DACs (Part number?)

Expect more questions when the above is taken care of. Also expect
advice from people who read this group who can trivially show you
how to design the best signal conditioning circuitry for this
application, but only if they have a clear picture of what you
need. This doesn\'t mean they will just give you the complete
design, but you might learn something.

If you have different sensors with very different characteristics
then one schematic per sensor may be needed.

At this stage I\'d be using a hand drawn schematic but ASCII art is
ok.

Enjoy your ice cream.

Sorry, that is your initial misunderstanding. I am not asking for
design advice. I am asking for someone who remembers the thread
where this was discussed a few months back. I\'m not able to find
it.

I searched GG with \"PWM DAC accuracy\", and the first thread that came up
was \"Attainable PWM accuracy?\" from a year ago.

Thanks, that\'s not the thread. I did searches for splitting the voltage rail to half voltage which is what I recall and didn\'t find anything. This isn\'t really PWM because it\'s a fixed 50/50 duty cycle. I didn\'t see anyone in that thread discussing such a division.

Maybe I imagined it or it was in another forum entirely. I recall the guy doing it was talking about secondary impacts on the accuracy such as unequal impedances in the high and low states of the output. Wouldn\'t be the first time an old guy\'s memory failed him.

I had forgotten that the resistor accuracy becomes a secondary effect on accuracy, so I\'m happy to use this to get very low error in the Vref with a single resistor.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[Rickster C]

On Thursday, November 5, 2020 at 5:02:57 PM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:66d7fde9-3d00-4b80-ab36-5b46ab269a47o@googlegroups.com...
On Thursday, November 5, 2020 at 3:01:21 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com....
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5,
Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying this
specific ventilator (if that\'s what it is) so that if I ever end up in a
hospital I can refuse to let them use it on me.

lol So do you have anything constructive to offer?

I think enough has already been offered.

I find it amazing that you need full specifications of everything in the
design

I\'m not surprised because I haven\'t asked for \"full specifications of
everything in the design\" just a reasonable description of what you\'re
trying to achieve with your sensor to ADC circuit.

to talk about generating a half Vcc voltage using a 50/50 duty cycle
digital output.

No-one except you would generate an ADC reference voltage like that.
I\'m not saying it won\'t work, and if you\'re trying to reduce component cost
to an absolute minimum then it may help with that.
But it wouldn\'t be my first choice for an ADC reference voltage in a
hospital ventilator.

You are asking questions about the cabling of the sensor to the board, a circuit that is not even connected to the reference voltage except through the power rails.

Ok, the sensor is mounted on the same PCB with an unspecified layout and an unspecified circuit to the ADC input, but will like be either a simple wire, or a pair of resistors as a voltage divider. The sensor provides an output voltage at a ratio to the sensor supply voltage depending on the signal being measured.

The inverting input to the differential comparator has a capacitor to ground, a resistor from the feedback output and either a series resistor from the sensor or a voltage divider from the sensor acting as a series resistor and reducing the voltage.

None of that is in electrical contact with the non-inverting input which will be connected to a capacitor to ground and a series resistor to an output switching at a high frequency up to 33.55 MHz.

I assume if you are blind you are reading this via a text reader? My 94 year old friend who is blind uses an ORCAM device to read magazines. He is a military collector and is still doing research in his specialties. The device has a hard time with many of the terms. .22 cal reads as \"twenty two California\". WWII reads as \"dubya dubya eleven\". Sometimes it\'s just totally lost because it fails to understand punctuation. When he bought it they said he could get updates to improve the product. They never said they would produce updates and they have not. Stinking Orcam! My friend is pretty durn impressive really. He is just not giving up no matter what. Still doing the independent living thing, but he does make me think about my own mortality when I think about his.

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b6a7ffbb-1ab8-4ca2-8363-79efc89d0c79o@googlegroups.com...
On Thursday, November 5, 2020 at 5:02:57 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:66d7fde9-3d00-4b80-ab36-5b46ab269a47o@googlegroups.com...
On Thursday, November 5, 2020 at 3:01:21 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5,
Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying
this
specific ventilator (if that\'s what it is) so that if I ever end up in
a
hospital I can refuse to let them use it on me.

lol So do you have anything constructive to offer?

I think enough has already been offered.

I find it amazing that you need full specifications of everything in
the
design

I\'m not surprised because I haven\'t asked for \"full specifications of
everything in the design\" just a reasonable description of what you\'re
trying to achieve with your sensor to ADC circuit.

to talk about generating a half Vcc voltage using a 50/50 duty cycle
digital output.

No-one except you would generate an ADC reference voltage like that.
I\'m not saying it won\'t work, and if you\'re trying to reduce component
cost
to an absolute minimum then it may help with that.
But it wouldn\'t be my first choice for an ADC reference voltage in a
hospital ventilator.

You are asking questions about the cabling of the sensor to the board, a
circuit that is not even connected to the reference voltage except through
the power rails.

Ok, the sensor is mounted on the same PCB with an unspecified layout and an
unspecified circuit to the ADC input, but will like be either a simple
wire, or a pair of resistors as a voltage divider. The sensor provides an
output voltage at a ratio to the sensor supply voltage depending on the
signal being measured.

The inverting input to the differential comparator has a capacitor to
ground, a resistor from the feedback output and either a series resistor
from the sensor or a voltage divider from the sensor acting as a series
resistor and reducing the voltage.

None of that is in electrical contact with the non-inverting input which
will be connected to a capacitor to ground and a series resistor to an
output switching at a high frequency up to 33.55 MHz.

Don\'t you think that if schematics were best done in words then that is how
they would be done?
For some reason most people don\'t seem to do their schematics in words, they
use schematics instead. Why would that be?

Imagine what music would be like if learning to play the piano required
reading a book along the lines of:
First press middle C and hold it for half a second, at the same time press G
a bit harder but hold it for one second and then also press E for two
seconds. etc.
For some reason it\'s not done like that. Why?

 

[Rickster C]

On Thursday, November 5, 2020 at 9:15:39 PM UTC-5, Edward Rawde wrote:

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:b6a7ffbb-1ab8-4ca2-8363-79efc89d0c79o@googlegroups.com...
On Thursday, November 5, 2020 at 5:02:57 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:66d7fde9-3d00-4b80-ab36-5b46ab269a47o@googlegroups.com...
On Thursday, November 5, 2020 at 3:01:21 PM UTC-5, Edward Rawde wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:ece32ce1-8aaa-432f-a9d9-15e710343b16o@googlegroups.com...
On Thursday, November 5, 2020 at 12:16:15 PM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:76f6cdfc-5cde-4332-a9ff-6e04aa85017bo@googlegroups.com...
On Thursday, November 5, 2020 at 1:29:45 AM UTC-5, Edward Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:511ea29c-87dc-448a-a320-17bea2237fb8o@googlegroups.com...
On Wednesday, November 4, 2020 at 11:33:01 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:b8a6337f-5b71-402c-a811-e39363d9f58bo@googlegroups.com...
On Wednesday, November 4, 2020 at 10:09:53 PM UTC-5, Edward
Rawde
wrote:
\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in
message
news:2709d197-5bd1-4d0c-9a6c-5baff6594b22o@googlegroups.com...
On Wednesday, November 4, 2020 at 5:01:49 PM UTC-5, Jeroen
Belleman
wrote:
On 2020-11-04 22:56, Jeroen Belleman wrote:
On 2020-11-04 22:00, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5,
Robert
Baer
wrote:
Rickster C wrote:

I am not asking for design advice.

In that case could you please give me a simple means of identifying
this
specific ventilator (if that\'s what it is) so that if I ever end up in
a
hospital I can refuse to let them use it on me.

lol So do you have anything constructive to offer?

I think enough has already been offered.

I find it amazing that you need full specifications of everything in
the
design

I\'m not surprised because I haven\'t asked for \"full specifications of
everything in the design\" just a reasonable description of what you\'re
trying to achieve with your sensor to ADC circuit.

to talk about generating a half Vcc voltage using a 50/50 duty cycle
digital output.

No-one except you would generate an ADC reference voltage like that.
I\'m not saying it won\'t work, and if you\'re trying to reduce component
cost
to an absolute minimum then it may help with that.
But it wouldn\'t be my first choice for an ADC reference voltage in a
hospital ventilator.

You are asking questions about the cabling of the sensor to the board, a
circuit that is not even connected to the reference voltage except through
the power rails.

Ok, the sensor is mounted on the same PCB with an unspecified layout and an
unspecified circuit to the ADC input, but will like be either a simple
wire, or a pair of resistors as a voltage divider. The sensor provides an
output voltage at a ratio to the sensor supply voltage depending on the
signal being measured.

The inverting input to the differential comparator has a capacitor to
ground, a resistor from the feedback output and either a series resistor
from the sensor or a voltage divider from the sensor acting as a series
resistor and reducing the voltage.

None of that is in electrical contact with the non-inverting input which
will be connected to a capacitor to ground and a series resistor to an
output switching at a high frequency up to 33.55 MHz.

Don\'t you think that if schematics were best done in words then that is how
they would be done?
For some reason most people don\'t seem to do their schematics in words, they
use schematics instead. Why would that be?

Imagine what music would be like if learning to play the piano required
reading a book along the lines of:
First press middle C and hold it for half a second, at the same time press G
a bit harder but hold it for one second and then also press E for two
seconds. etc.
For some reason it\'s not done like that. Why?

How does a blind guy who can\'t read the drawing I gave him read a schematic?

Clearly you are a troll. Go away!

--

Rick C.

+++ Get 1,000 miles of free Supercharging
+++ Tesla referral code - https://ts.la/richard11209

 

[Edward Rawde]

\"Rickster C\" <gnuarm.deletethisbit@gmail.com> wrote in message
news:05637010-ee43-4637-9fd3-b2d0df72e432o@googlegroups.com...
On Thursday, November 5, 2020 at 5:19:29 AM UTC-5, piglet wrote:
On 04/11/2020 9:00 pm, Rickster C wrote:
On Wednesday, November 4, 2020 at 2:56:03 PM UTC-5, Robert Baer wrote:
Rickster C wrote:
I recall a thread sometime in the last year that mentioned an idea
for generating an accurate voltage at half the supply rail by
switching an output at a 50/50 duty cycle to feed an RC. I can\'t
seem to find that thread. I\'m wondering what the limitations might
be on the accuracy. Obviously the difference in drive capability is
a factor, but that can be mitigated by the external resistor.

i suppose there can be differences in the delay times for the two
edges within the digital device. That can be mitigated by using a
slower cycle. To get a 0.1% tolerance with a ±1 ns timing variation
requires the waveform be 0.5 MHz.

Any ideas on other points that may be important? I suppose a quality
integrating capacitor might be important as well. Also ceramic caps
can be microphonic, so film caps will be needed. In fact I need to
specify that all through the sensor power supply.

You mean \"half voltage\".

Thanks, but trying that both with and without the quotes didn\'t turn up
the thread going all the way back to December. It couldn\'t have been
that long ago could it? Seems like maybe three for four months back.

I\'m not sure how bad it would be to simply use a pair of 0.1%
resistors. That would add error somewhere between 0.1% and 0.2% (not
thinking about it too hard). There will be other sources of error from
this same effect elsewhere (dividing the 5V signal source to 3.3
volts... or maybe not. Perhaps that can be mitigated by not using
equal value resistors in the input and feedback paths.

It\'s funny that the other guys on the project don\'t seem to be able to
think about this stuff. I guess they are mostly used to just plopping
down chips. Heck, a new FPGA guy wanted to use a $20 Xilinx part
instead of a $4-5 Gowin part!

I was happy to find I can get 10 nF C0G for under a nickle and 100 nF
for around a dime. I thought they didn\'t come that large. They do get
large!


If you don\'t think the 0.1% resistive divider is good enough can\'t you
calibrate it out during power-on self test? Or even add a analog switch
mux upstream for sensor sanity checking?

Please tell meh ow to calibrate absolute accuracy? I still don\'t follow
why such a simple technique should not be used.

What does the mux do???

I thought you said you didn\'t want design advice.

--

Rick C.