Pressure sensor and MCU ADC

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View


Well, I tried using the net to find a simple answer for this - without
much luck, so thought I'd at least ask here again hoping that someone
has done something similar.

What started this was my volunteering to make a grey water pump with
auto cutout. I've at least created a board using an Atmel ATtiny13,
pushbutton and relay. The timeout and pushbutton code is working, but
I've yet to interface a pressure switch to an ADC input indicating
lack of water pressure.

I was given an SX01DN sensor to test (see
http://www.farnell.com/datasheets/51886.pdf )
and please forgive my ignorance (or stupidity), but I really can't see
how to interface this with an MCU without substantial op-amp
circuitry. Even then, how to get an output range of 0-5 volts is still
beyond me at this stage.

Any hints would be appreciated, any 'you d***head' messages not <g>.

Cheers, Phil.


Re: Pressure sensor and MCU ADC



Quoted text here. Click to load it
http://www.farnell.com/datasheets/51886.pdf )
Quoted text here. Click to load it

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
We've slightly trimmed the long signature. Click to see the full one.
Re: Pressure sensor and MCU ADC


Quoted text here. Click to load it

In the PDF you mention, there's a circuit Fig V, page 5 and 7  to give ADC
scaling and offset adjustments.

VO  goes to the input of the ADC.

While it looks simple enough... your first instrumentation sensor project
like this will be a challanage and ultimate reward  if you get it going.

Joe



Re: Pressure sensor and MCU ADC


Thanks Joe G,

Much appreciated indeed. When I get it working I'll send you the
project (only if you're interested of course).

I assume you watch 'Iron Chef' also :-).

Quoted text here. Click to load it




Re: Pressure sensor and MCU ADC


Phil,

I have done this with other makes of pressure sensor.  More expensive
devices have inbuilt amplifying circuitry however for yours you will need an
opamp. With the right set of resistors you should be able to scale the data
to 0-5V.  The data sheet gives an example.  For accurate values it needs
temperature compensation also.  You should be aware that your pressure
sensor is not really suitable for contact with liquids and therefore you
will probably need to isolate it.  The usual method is with a bubbler.  An
aquarium pump will be OK for 1 psi

If you just want a cutout then a $10 float switch is the cheapest and
easiest solution.  Very simply on-off condition that can easily be read by
one microcontroller pin.

Regards

Pete
Quoted text here. Click to load it



Re: Pressure sensor and MCU ADC


Thanks also Peter,

Nice idea with the bubbler BTW.
I had thought of a float switch also, but then I wouldn't learn how to
interface a pressure sensor, also I need to keep the complexity level
high :-)

Much thanks again, Phil.




Re: Pressure sensor and MCU ADC


[Oops! - Please pardon the empty reply I just posted accidentally.]

On 20 Mar 2007 02:07:30 -0700, snipped-for-privacy@gmail.com wrote:

Quoted text here. Click to load it

Do you need to actually measure exact pressure, or do you just need
know whether it's above or below some point? Considering your
application, I think that making a proper pressure-measuring
instrument is massive overkill. ;^)
 If so, I'd just connect one of the two outputs to a comparator &
connect the other comparator to a trimpot. You'd need to measure the
output voltage at the pressures you'll be using it with to see if it
changes enough to detect reliably, & given that your switching doesn't
sound like it needs respond very fast, I'd put a small (1nF?) cap
between the output & ground to keep noise from causing
false-triggering.

(Note that the two outputs are simply voltage dividers that go in
opposite 'directions', so I'm guessing that a single output will give
you half the volt/PSI output, compared to measuring the differential
between the two outputs the way you normally would with a Wheatstone
bridge.)

 I'm not familiar with the Atmel MCUs, but if it has comparator input,
you could use that, & if it's like some of the PICs & has a comparator
that can be connected to an internal DAC, you could skip the trimpot &
set the trip point in software.

(PS: you should probably still temperature-compensate the sensor
anyway. I'd just use the simple 4 diode circuit on page 5 of the
datasheet.)


--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
We've slightly trimmed the long signature. Click to see the full one.
Re: Pressure sensor and MCU ADC


Hi Lionel,

Well, I was wondering why you previous message only contained a tag
line, and after a bit of self-reflection assumed you were referring to
myself..
"Some people are alive only because it is illegal to kill them."
Anyway, after meditating on that for a while and hiding the sharp
knives in the kitchen found that you had posted an excellent response.

That's exactly what I was after (excluding op-amps). Now working out
how to do it is another challenge.

Thanks heaps, Phil.


Re: Pressure sensor and MCU ADC



Quoted text here. Click to load it

Yes, sorry about that. I hit 'reply', & cleverly bumped the mouse
button against one of the monitors whle the cursor was over the 'send'
button.

Quoted text here. Click to load it

I've been using this .sig for nearly ten years, you'd amazed at how
good a net-kook detector it is. Every now & then, somebody takes it
seriously, & thinks it's directed specifically at them. So far, each
one of them has been a genuine nutcase, & their reaction is usually
hilariously funny. The best ever was the infamous Archimedes
Plutonium, who wnet into hysterics about my 'death threat' towards
him, & complained unsuccessfully to my Internet provider, then spent
weeks spamming the net-abuse administrative groups, trying to get me
banned from Usenet. ;^)

Quoted text here. Click to load it

Always a wise move. ;^)

Quoted text here. Click to load it

Thanks Phil.


Don't thank me too loudly until it's working. The one thing I'm not
sure about is whether you'll get enough voltage swing on one output to
reliably switch a comparator, & noise might be a problem. The rest of
my advice should be reasonably reliable, insofar as that's possible
without me actually breadboarding & debugging it.

OTOH, if all goes well, you can shout me a beer if our paths cross. ^)

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
We've slightly trimmed the long signature. Click to see the full one.
Re: Pressure sensor and MCU ADC



Quoted text here. Click to load it
Another method in the 'Kiss' principle, is to use a pressure switch from a
dishwasher or washmachine.
No electronics or pics, it just switches the mains directly and is very
reliable !!

--
Cheers .......... Rheilly P



Re: Pressure sensor and MCU ADC


On Tue, 20 Mar 2007 21:57:28 +0800, "Rheilly Phoull"

Quoted text here. Click to load it

Excellent suggestion, Rheilly.

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
We've slightly trimmed the long signature. Click to see the full one.
Re: Pressure sensor and MCU ADC



Quoted text here. Click to load it
http://www.farnell.com/datasheets/51886.pdf )
Quoted text here. Click to load it

Intersema manufactures a range of pressure sensors with digital outputs,
obliviating the need for any analog amplifier or buffer circuitry. We used their
MS5534 with great success. Pricey though.

http://www.intersema.ch/site/technical/products_guide.php

A simple pressure switch, or a float switch should be a more cost effective
solution.


Re: Pressure sensor and MCU ADC


Thanks dmm,

Yep, pricey is good if it's not a hobby project and the idea of a
pressure switch is sounding like a better option.

Another option my mate with less electronics knowledge than myself (if
that's possible) suggested is 2 pin probes close together into the
water outlet pipe at a high point. I think that may just work in this
case.

Quoted text here. Click to load it
their
Quoted text here. Click to load it

solution.



Site Timeline