Suitable sensor for meaasuring air pressure inside balloons, beach balls, boats.

Projects General Guidance
1

Hi all,

I'd like to measure the air pressure inside inflatable items like couches, pool loungers, pool floats etc.

The idea is to work out a 'target' pressure, and then use a speed controller along with an electric air pump to top up to this pressure if (say, due to a small puncture or a leaky valve) it drops below.

I imagine the sensor would need to be sensitive to fairly small changes in pressure, as I don't think there's a huge difference in pressure between a normally inflated chair and a saggy one. However, I doubt a normal weather-reading barometric sensor would be suitable for the pressure when laden.
I don't know what the pressure is inside an airbed with 80kg on it. It might spike when the person first gets on (so this would need to not break the sensor), but I doubt I need the full pressure range of sensors designed for vehicle tyres.

The idea is to put the sensor in the hose that's inflating the item, though I realise there'll be some difference between the pressure in the hose and in the item itself, so the system may pause inflating from time to time to get a more steady reading. It will need to be small enough to do this.

Reading other threads on air pressure on this forum, I realised I'll either need to understand op-amps (I've thus far failed to find an explanation that I didn't find hard to digest), or pick a sensor with a built-in amp.

I have no idea where to start looking for a sensor with a built-in amp, but I found what might be a couple of options.

There's the BMP085, which has break-out boards and stuff readily available (nice, as my soldering hands are not the steadiest), and it's almost certainly sensitive enough for my needs, but I'm not sure it's suitable for the pressures involved.

The 2SMPP-02 from Omron might do the job, but looking at its data sheet, I can't work out what voltage I should put across it. I also suspect I'd have to amplify the output.

Can anyone with more of a clue guide me in the right direction?

2

The datasheets for the various common BMP sensor models will tell you the information you need. I would definitely look at those since they're so cheap. On the other hand, the form factor might be a bit tricky to work with in this application. I like the pressure sensors the nice hose nipple connection built in, but the easy to use one are so expensive. I've used the Freescale MPVZ5010GW7U to measure somewhere around the pressure range you're working at, and it was very easy to interface with an Arduino by following the reference schematic in the datasheet. But those things are about $17 after shipping from Digikey!

3

I'd like to measure the air pressure inside inflatable items like couches, pool loungers, pool floats etc.

Start by using a tire pump with pressure gauge to inflate various items, to inform yourself about the pressures in question. Then select a sensor with range to match.

4

I use Autex or Eyourlife Pressure sensors available through Amazon. They come in various pressure ranges. They are more expensive (about $18 USD) each but they make up for it in ruggedness and ease of use. They are 5 Volt powered and their output runs from 0.5V to 4.5V Full Scale.

They are made from stainless steel and have a 1/8" NPT fitting on them. Just plug them into your 5 volt supply and input the signal line to one of the analog pins and you are up and running. The cost is more than made up by the fact that once installed I can forget them for years, indoors or out (they have an automotive watertight type connection.)

5

Look at the MPX5100 and its siblings - a family of differential air pressure sensors, available for various pressure ranges. Which one to choose depends largely on the pressure you need (and which indeed you have to measure). Ratiometric analog output making it really easy to read with an Arduino.

The BMP280 goes up to 1,300 kPa, so not much higher than ambient pressure. Probably too low for inflatable gear.

6

I'd build multiple devices (pump + sensor + hose coupling) for various pressure and volume ranges.