Post by thread:pressure sensor with PICs

At 16:39 21/09/98 +0300, you wrote: >Has anyone any leads concerning cost effective pressure sensors to be >interfaced to PICs. The sensors should have analog output 0-5Volts, & >pressure range is 0-15 bars or 0-140 psi. Honeywell make a variety of pressure sensors, available in the UK from Farnell, and presumably others... The one I am looking at now is a 24PCGFMIG, 0-250psi. The voltage output is lower than you need (it's actually a resistive bridge), but an op-amp booster isn't hard to make. We're planning to use them to measure depth in sea water- ideally I'd like one with a built in 0psi reference, as we will be relying on our sealant to block off the rear reference port. Anyone seen such a part, which will work to similar pressures? Or anyone with any advice on sealing the above sensor successfully? Nigel -- Nigel Orr Research Associate O ______ Underwater Acoustics Group, o / o \_/( Dept of Electrical and Electronic Engineering (_ < _ ( University of Newcastle Upon Tyne \______/ \(

Norayr: I have done similar project a few months ago. I used pic16c71 connecting it through single Opamp. normally you have to use more then 1 opamp depending type of sensor you have. if you buy more expensive one it has opamp in it then you can directly interface it to any pic analog input. I played with it a lot. it is a nice toy. I used 6 pressure sensors each sensor cost me 15$ I got it from newark. if you need more info let me know. in my application just needed to turn the timer on and off. Andre Abelian. Norayr S. Elmayan wrote: > Has anyone any leads concerning cost effective pressure sensors to be > interfaced to PICs. The sensors should have analog output 0-5Volts, & > pressure range is 0-15 bars or 0-140 psi. > > Thank you

Norayr asked: >Has anyone any leads concerning cost effective pressure sensors to be >interfaced to PICs. The sensors should have analog output 0-5Volts, & >pressure range is 0-15 bars or 0-140 psi. > Motorola Sensym all have low-cost sensors Fujikura Motorola and Sensym both have web pages. Fujikura can be contacted through their US distributor, Servoflo Inc., 617-862-9244. Reg Neale

part 0 625 bytes content-type:application/octet-stream; (decoded 7bit) >Has anyone any leads concerning cost effective pressure sensors to be >interfaced to PICs. The sensors should have analog output 0-5Volts, & >pressure range is 0-15 bars or 0-140 psi. > >Thank you > Here's a link to pressure sensors which look useable. Larry Content-Type: application/octet-stream; name="SENSEON Pressure Sensors.url" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="SENSEON Pressure Sensors.url" Attachment converted: wonderland:SENSEON Pressure Sensors.url (????/----) (0001753C)

the only pressure sensor mats i have seen are for alarm systems or automatic doors (like at the super market) these are contact switches and have low resistance. if you want weight then you have to use something like a load cell (expensive) although i once heard that peizo devices will emit a voltage based on the pressure applied. my question is "Can this be used as a crude +/- 1 pound scale with a range of 5-30 pounds?" it's for a totally different idea. michael You may leave the list at any time by writing "SIGNOFF PICLIST" in the body of a message to spam_OUTLISTSERVTakeThisOuTMITVMA.MIT.EDU. {Original Message removed}

> where Jameco had them once, ask a local alarm systems supplier/dealer. > dealt with it I have, but for their original application, which is intrusion sensing. > linear Out of this point of view, they are in the 'forget it' class. Not only are they not linear, but the actual contact resistance varies with a lot of parameters (such as what kind of shoes etc). You also have to make sure that you get the electrical and not the pneumatical variety, the latter using a conductive rubber switch actuated by a diaphragm, as opposed to a full surface grid. Peter

On Tue, 22 Sep 1998, Michael Hagberg wrote: > (expensive) although i once heard that peizo devices will emit a voltage > based on the pressure applied. my question is "Can this be used as a crude > +/- 1 pound scale with a range of 5-30 pounds?" it's for a totally different > idea. You want an accuracy of slightly worse than 3%. This can be done with a piezo element. I'll outline the principle: The piezo cell generates voltage as soon as it is deformed. The polarity of the voltage depends on the sign of the force applied. The voltage rises with a speed that depends on the speed of weight application to a level that depends on the force and then decays slowly as the piezo is a capacitor with losses. The integral of the generated voltage is a direct measure of the work executed by the placing of the weight on the scale. Thus, if one integrates this voltage over the time it rises, one obtains a quantity that is linearly related to the energy stored in the elastic piezo material: W = K * X^2 Since K is very large and dx very small one can approximate X ~= X^2. So, all you have to do is sample and hold the integral of the voltage and scale it with a constant to obtain weight... For some real world numbers, take a 20 mm pizo speaker disk to be loaded with 500 grams, placed on it by hand (the disc is supported on the rim, the load is placed on the metal side, in the middle, using a 1:1 lever), one obtains a voltage spike in excess of 20 Volts with a duration of about 0.8-1 sec (the time to place the weight on it), without major jumps. Peter

I just recently saw an article in Sensors Magazine for a variable resistance type thin flexible film type pressure sensor that might do the trick. There are several load ranges starting with 0-2 PSI and going up to 0-25000 PSI. The active areas of these things is a disc about 0.375 in in diameter. The single sensors with no signal conditioning (basically a variable resistor) are about $55 for 2 if I remember correctly. They even have matrix type with thousands of elements to check detailed pressure variations over a large area. I called the company and got a brochure: Tekscan, Inc., 307 W. First Street, South Boston, MA 02127-1342. Phone: 800-248-3669 ask for information and pricing for both the Flexiforce transducers and the ELF measurement systems. Also there is a piezofilm type stuff available from MSI (http://www.msiusa.com/piezo_film.htm) if I'm not mistaken, which you can connect wires to and get a voltage by pressure, stretching, or bending -- I believe you can call and get some free samples for evaluation. They also make coaxial cable of the stuff for traffic sensors to be embedded in the road. There's an electronics interfacing application note at: http://www.amp.com/product/articles/interface.html -- AMP was the original company that manufactured these things. Steve Brown -- ------------------------------------------------------------------- Stephen Brown, Ph.D. New England Research 76 Olcott Drive White River Junction, Vermont 05001 USA (802) 296-2401 phone (802) 296-8333 fax .....sbrownKILLspam@spam@ner.com http://www.ner.com http://www.dartmouth.edu/artsci/rox -------------------------------------------------------------------