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Pressure sensor and MCU ADC

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.
 
J

Joe G \(Home\)

Jan 1, 1970
0
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.

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
 
P

Peter

Jan 1, 1970
0
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
 
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 :).
 
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.
 
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.
 
R

Rheilly Phoull

Jan 1, 1970
0
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.
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 !!
 
D

dmm

Jan 1, 1970
0
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.

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.
 
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.
 
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