That's an absolute pressure sensor; you want a differential one with the atmosphere as the reference pressure.
Motorola used to make pressure sensors as a board-level part. I assume these were spun off into Freescale although they may be On semiconductor parts now. You'd have to build a little board to interface to an ADC.
Or try these folks:
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Freescale's parts are good, I'm sampling them now. They have a version with integrated hose barb, very convenient. The ADC-1R2 from Superlogics is a serial-connected ADC which is very suitable for reading this type of device; I'm not sure if Superlogics has a USB version, but the ADC-1R2 is easily connected via USB-serial converter.
Hi,
Freescale have a good variety of pressure sensors, they are about $10-$15US from digi key
As for connecting to a computer, personally I use a Microchip PIC with RS232, if you want USB and do decide to use a microcontroller for A/D conversion I'd still use RS232 and buy an off the shelf RS232-USB converter. Playing with USB in microcontrollers seems more bother than it's worth.
Good luck!
Hi all,
I'd much appreciate any advice on my search for a cheap and simple pressure sensor. I need to make a device which can measure how hard a baby is squeezing a silicon tube, around 2cm thick. I figure the best way is to connect the tube via a pneumatic tube to a pressure sensor. So what I need is a pressure sensor that does not have to be accurate in absolute terms, but needs to 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 drivers which provided an API. Alternatively, if you know a good one but it just outputs a voltage, perhaps you could also recommend a good cheap and cheerful USB A to D converter?
So far the best thing I've found is this, which you can combine with a USB interface from the same supplier:
Other solutions to the basic problem also gratefully received!
Cheers,
Ben
-- Dr. Ben Kenward Department of Psychology Uppsala University, Sweden http://www.benkenward.com
Dr. Ben, an inexpensive solution might be to salvage the pressure sensor and electronic from an inexpensive, broken, blood pressure monitor. (Usually the compressor on these little boxes fails well before its other components.)
Off-the-shelf solutions are available, but tend to be costly.
Harry C.
You may use my pressure sensor.
Download OA_Pressure_Probe at
"Ben" a écrit dans le message news: Xns96EEDD671280Fbenjaminkenwardzoolo@163.1.2.7...
pressure
it
Hi all,
thanks very much for all your advice. Those Phidgets look perfect for me... I'm not averse to getting my soldering iron out once in a while but it looks like I could avoid it completely with those and save a bit of time. They are dead cheap too.
Cheers,
Ben
-- Dr. Ben Kenward Department of Psychology Uppsala University, Sweden
Ben wrote in news:Xns96EEDD671280Fbenjaminkenwardzoolo@163.1.2.7:
Put a piece of black anti static foam (like the kind you put IC's in) between 2 pieces of metal (I used PCB material) That is the cheapest way I know about.
Frank
Ben wrote:
The answer really depends a lot on volume, financial requirements, and exact specifications. If you are are looking for a one-off system and willing to spend the money, you can buy an integrated pressure sensor (Motorola makes some for instance) with voltage output and a data aquisition board
There are a few things you didn't mention in your post in terms of requirements:
1) How much resolution do you need? (I presume that "accuracy" must be to at least +/- 1/2 of the resolution) 2) How much full-scale range do you need? 3) How many samples per second do you need? (presumably this would be on the order of 1 per ms, and not a major requirement) 4) You mention that you do not care about absolute values, so it sounds like you don't care about an offset in the result. But do you care about an offset that changes over long periods of time or over temperature? 5) Do you care about absolute gain (i.e. Does a specific pressure change have to correlate to a specific output change)? 6) If you do not need an absolute gain, do you need to ensure that the gain doesn't change over long periods of time or over temperature? 7) Can you calibrate against a known accurate sensor either at production or at any time in the future?Accuracy is going to be a function of three things: the pressure sensor, the A/D converter, and the signal processing between the two. The easiest solution I can think of for the A/D conversion and computer interface that doesn't include buying a premade board is to buy an 8-bit microcontroller that has a built in USB interface and A/D converter. However, make sure that the microcontroller's A/D converter is adequate for your required task, otherwise you'll have to buy an external one (if you are trying to get very accurate/high resolution #'s at relatively slow speed (< 10k samples a second) you may be best off with an external sigma delta A/D, but it may be overkill).
While integrated pressure sensors are very easy to use, it may be cheaper and more accurate to get a dedicated current bridge style sensor. This will require more sophisticated signal processing, possibly aided by digital calibration in the microcontroller. I only recommend going this route if you are forced to by the specifications of the project or if you are going for very high volume (and it actually saves money).
The signal processing could range from virtually nothing to a carefully designed current source, filters, and precision operational amplifier setup, and again will vary completely on the requirements of your project.
good luck, dan
pressure
it
What about a salt water filled manometer? The salt water forms one plate of a capacitor. The other plate is metal foil surrounding the plastic tube manometer. Pressure causes the salt water to rise in the tube increasing the capacitance. Put that capacitance into a square wave generating circuit, 555 for example, and then measure the changes in output frequency.
R1000 KPa? These are baby gorillas? Bionic babies?
$75 gas pressure sensor
with $59 GoLink! USB acquisitin unit.
Are you measuring pressure or force? Pressure will depend on the surface area acted upon which will depend on the child's grip.
Force could be easily measured with a strain gauge attached to a suitably designed spring. Something like a metal rod bent into a long, narrow U shape, 2 cm across. If you can't control the direction that the baby will squeeze, place two such springs at right angles inside the tube, measure the strain in each axis and sum their vector quantities in software.
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Due to recent budget cuts, the light at the end of the tunnel has temporarily been turned off.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.