advice on a simple pressure sensor?

Question

Hi all,I'd much appreciate any advice on my search for a cheap and simplepressure sensor. I need to make a device which can measure how hard ababy is squeezing a tube, around 2cm thick. I figure the best way is touse a silicon tube, just above atmospheric pressure, and connect it viaa pneumatic tube to a pressure sensor. So what I need is a pressuresensor that does not have to be accurate in absolute terms, but needsto be relatively sensitive, so it can measure changes in grip strength.I reckon if it went up to 1000 kPa that would be more than enough.Preferably it would come with an integrated USB interface and driverswhich provided an API. Alternatively, if you know a good one but itjust outputs a voltage, perhaps you could also recommend a good cheapand cheerful USB A to D converter?So far the best thing I've found is this, which you can combine witha USB interface from the same supplier: I think it will only interface using their proprietary software -it's for classroom use, after all. But this gives you a basic idea ofwhat I'm after.Other solutions to the basic problem also gratefully received!Cheers,Ben--Dr. Ben KenwardDepartment of PsychologyUppsala University, Sweden

blaildyors · Accepted Answer

1000kPa is ~145PSI! It's going to be one strong baby?!You're going to need a design but here's how I would go about it - Iwould connect the silicon tube directly to the sensor and seal the openend. Before use I would take a reading from the sensor without the babysqueezing the tube and uses this as a baseline (this would removeambient conditions such as room temperature and altitiude), then getthe baby to squeeze and take a reading then subtract the baselinereading from the measured reading. The trouble is babies are not alwaysthe most cooperative and like the other poster mentioned the heat fromthe hands would effect the readings if the tube was held too long. Thewall of the tubing would have to be pretty thin so as not to damp thereadings too much as I wouldn't think the baby will have a very stronggrip. I have a sensor (but is is just sensor with a voltage o/p -nothing more) in mind but don't have the info to hand at the moment;will try to dig the info out tomorrow.amorphia wrote:

CWatters · Answer

Presumably you will also need to correct for temperature - The baby's handwill warm up the air in the tube causing the pressure to rise even if theydon't squeze it.

blaildyors · Answer

Sensor would need to be waterproof.The sensor I was thinking of was the motorola MPX2200A (0-29PSI) orsimilar (try googling for datasheet) - silicone tube would connectdirectly to the port on the sensor.

Andy Baxter · Answer

have 'quantum tunnelling compound pills', which work as pressure sensors -you could embed one or two in a piece of rubber and use that.you could also trywho sell a conductive rubber that changes conductivity when under pressure.-- remove 'n-u-l-l' to email me. html mail or attachments will go in the spambin unless notified with [html] or [attachment] in the subject line.

Zak · Answer

Fill the tube with a liquid: less expansion.Thomas

Rich, Under the Affluence · Answer

I seriously doubt if he'll get much of a reading at all from a silicontube.Silicone, maybe.Cheers!Rich

Bob Eldred · Answer

1000kPa??? That's about 10 Bar or 150 PSI. What baby is going to be able tocreate that pressure squeezing on a tube? You're going to have to be about100 times more sensitive than that, say 10kPa or 1.5 PSIG (gauge pressure)to be effective. That's about 100cm of water. Get a cheap pressure gauge andplay around with it first before you try to instrument it.Bob

advice on a simple pressure sensor?

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