From Newsgroup: sci.electronics.design

On 12/26/2025 7:13 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure? I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

They operate on air pressure. The rising water level closes off the
bottom end of a chamber; thereafter any further increase in water level causes an increase in air pressure within the chamber. A very flexible rubber diaphragm presses aginst a spring and eventually operates a microswitch.

Yes, I know that from tinkering with old washing machines.
But, the mechanism was large (the size of a lemon).

By substituting a movement sensor for the microswitch (and with the use
of a suitable spring) you could make a proportional air pressure sensor
of good sensitivity which held its calibration to a reasonable degree of accuracy.

But, there are semiconductor devices already that do this for a
buck or two (in tiny quantities). They would be considerably
easier to deploy -- in large numbers. E.g., one typically
instruments an AHU in many places as the air is "processed"
within -- each observation point lets you close a loop
or infer something about that process.

I have also used a differential air pressure sensor that used a thin
silvered tensioned plastic diaphragm as a concave/convex mirror with a
light emitter and sensor on each side, connected to a balancing circuit.
It was exceptionally sensitive but not particularly robust or
repeatable.

The same problem (as above). You can use a chilled mirror to
detect dewpoint -- or, by changes in capacitance of polymers.
Big difference in size, cost, precision, durability, etc.

When you move away from thinking of sensors as needing "calibration",
you can approach problems with more flexibility.


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From Newsgroup: sci.electronics.design

On 12/26/25 11:37, Don Y wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure?-a I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

In systems that I've designed previously, someone
else selected (very expensive!) transducers and
I just had to interface with them.

But, those were industrial systems with dedicated
staff to keep them running, calibrated, etc.-a You
cared about the actual "numbers" from the sensors
because you were controlling "regulated" processes
and needed to document compliance/exceptions.

I'm trying to leverage some of those algorithms but in a
cheaper consumer market where stuff "just has to work".
I don't care about numbers as much as *trends*, using
adaptive algorithms to sort out what's "normal" from
"indicating".

I've had some fun with teeny tiny BME280 sensors. They
have a sub-1% absolute accuracy and enough resolution
to detect the pressure change between your head and your
feet. They measure temperature and humidity too. The
interface is I2C.

Jeroen Belleman
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From Newsgroup: sci.electronics.design

Jeroen Belleman <jeroen@nospam.please> wrote:

On 12/26/25 11:37, Don Y wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure? I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

In systems that I've designed previously, someone
else selected (very expensive!) transducers and
I just had to interface with them.

But, those were industrial systems with dedicated
staff to keep them running, calibrated, etc. You
cared about the actual "numbers" from the sensors
because you were controlling "regulated" processes
and needed to document compliance/exceptions.

I'm trying to leverage some of those algorithms but in a
cheaper consumer market where stuff "just has to work".
I don't care about numbers as much as *trends*, using
adaptive algorithms to sort out what's "normal" from
"indicating".

I've had some fun with teeny tiny BME280 sensors. They
have a sub-1% absolute accuracy and enough resolution
to detect the pressure change between your head and your
feet. They measure temperature and humidity too. The
interface is I2C.

Jeroen Belleman

Of course they might be detecting the difference in the mean molecular
weight of the local atmosphere. ;)

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
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From Newsgroup: sci.electronics.design

On 27/12/2025 11:35 am, Phil Hobbs wrote:

Jeroen Belleman <jeroen@nospam.please> wrote:

On 12/26/25 11:37, Don Y wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure?N++ I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

In systems that I've designed previously, someone
else selected (very expensive!) transducers and
I just had to interface with them.

But, those were industrial systems with dedicated
staff to keep them running, calibrated, etc.N++ You
cared about the actual "numbers" from the sensors
because you were controlling "regulated" processes
and needed to document compliance/exceptions.

I'm trying to leverage some of those algorithms but in a
cheaper consumer market where stuff "just has to work".
I don't care about numbers as much as *trends*, using
adaptive algorithms to sort out what's "normal" from
"indicating".

I've had some fun with teeny tiny BME280 sensors. They
have a sub-1% absolute accuracy and enough resolution
to detect the pressure change between your head and your
feet. They measure temperature and humidity too. The
interface is I2C.

Of course they might be detecting the difference in the mean molecular
weight of the local atmosphere. ;)

Even the smelliest feet don't make a significant difference to the mean molecular weight of the local atmosphere around your feet. The extra CO2
in the exhaled air around your head will raise the mean molecular weight
more, but still not enough for a pressure gauge to register.
--
Bill Sloman, Sydney

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From Newsgroup: sci.electronics.design

On 12/27/25 01:35, Phil Hobbs wrote:

Jeroen Belleman <jeroen@nospam.please> wrote:

On 12/26/25 11:37, Don Y wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure?N++ I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

In systems that I've designed previously, someone
else selected (very expensive!) transducers and
I just had to interface with them.

But, those were industrial systems with dedicated
staff to keep them running, calibrated, etc.N++ You
cared about the actual "numbers" from the sensors
because you were controlling "regulated" processes
and needed to document compliance/exceptions.

I'm trying to leverage some of those algorithms but in a
cheaper consumer market where stuff "just has to work".
I don't care about numbers as much as *trends*, using
adaptive algorithms to sort out what's "normal" from
"indicating".

I've had some fun with teeny tiny BME280 sensors. They
have a sub-1% absolute accuracy and enough resolution
to detect the pressure change between your head and your
feet. They measure temperature and humidity too. The
interface is I2C.

Jeroen Belleman

Of course they might be detecting the difference in the mean molecular
weight of the local atmosphere. ;)

Cheers

Phil Hobbs

Grmpf ;-)

While I was graphing the outputs, I was surprised by the efficiency
of humidity readings to detect human presence. The curve was quite
smooth with no one in the room, but got quite noisy with someone
present.

jeroen Belleman
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From Newsgroup: sci.electronics.design

On 2025-12-25, Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure? I'm looking at nominally an inch of water
(pressure/vacuum) but haven't sorted out the high end though
anything above those limits is probably easily treated as
"too high" instead of being numerically quantified (though
the sensor would have to survive the environment).

I'd prefer to use solid state sensors deployed *at* the point
of measurement (no/minimal "tubing") but worry about dirt, debris
and critters, over time.

If by "no tubing" you mean drill a hole in the duct fit a rubber grommet and then plug a barbed sensor into the grommet. that could work, putting the whole sensor inside the duct seems fraught.

Lead lengths would be on the order of 10-20 ft.

At 20 feet I2C would be tricky, but Analog sensors are available.

Perhaps a solution would be to just treat them as FRUs intended
for routine replacement? (instead of worrying about keeping
them clean, etc.)

Puting a sock over the connector will keep most junk out. maybe somethign like the
outer covering of parachute cord. I'm not sure where you buy that. There's probably
somethig better available.

Installing the sensor with the aperture facing downwards will help too.
--
Jasen.
Efc|Efca -i-+-#-#-# -u-|-C-#-u-+-u
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From Newsgroup: sci.electronics.design

Jeroen Belleman <jeroen@nospam.please> wrote:

On 12/27/25 01:35, Phil Hobbs wrote:

Jeroen Belleman <jeroen@nospam.please> wrote:

On 12/26/25 11:37, Don Y wrote:

On 12/26/2025 3:27 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:

Any pointers regarding deployment of pressure sensors measuring
air pressure?N++ I'm looking at nominally an inch of water
(pressure/vacuum)...

Washing machine/diswasher water-level switches?

No, I'm looking at pressures in air handling systems.

In systems that I've designed previously, someone
else selected (very expensive!) transducers and
I just had to interface with them.

But, those were industrial systems with dedicated
staff to keep them running, calibrated, etc.N++ You
cared about the actual "numbers" from the sensors
because you were controlling "regulated" processes
and needed to document compliance/exceptions.

I'm trying to leverage some of those algorithms but in a
cheaper consumer market where stuff "just has to work".
I don't care about numbers as much as *trends*, using
adaptive algorithms to sort out what's "normal" from
"indicating".

I've had some fun with teeny tiny BME280 sensors. They
have a sub-1% absolute accuracy and enough resolution
to detect the pressure change between your head and your
feet. They measure temperature and humidity too. The
interface is I2C.

Jeroen Belleman

Of course they might be detecting the difference in the mean molecular
weight of the local atmosphere. ;)

Cheers

Phil Hobbs

Grmpf ;-)

While I was graphing the outputs, I was surprised by the efficiency
of humidity readings to detect human presence. The curve was quite
smooth with no one in the room, but got quite noisy with someone
present.

jeroen Belleman

WerCOve used the very nice Sensirion SHTC3 (rCLschtick #3?rCY) T/H sensor to calculate the dew point to monitor desiccant performance and prevent condensation. Super good medicine.

Cheers

Phil Hobbs
rCLThree French hensrCa.rCY
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
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