Shop Env Page

I have occasionally wished I had some way to check on things in the shop and be able to control them, from elsewhere via our network.   The shop has an AirCompressor system, Mini-Split AC, 6" & 2" dust collection sysem (2" system is on the drawing board now).  

I bought a 150 PSI air pressure sensor from Amazon.   I found lots of simple sketches on the web about reading and correcting the reading, but they all needed to know what the max reading was to the sensor's max pressure.   I had a 150 PSI pressure gauge and only 120 PSI to test with.   So I took several readings at zero PSI, 50 PSI, and 100 PSI, the using the correcting aquation, solved for max reading.   In my case it is 790 (895 uncorrected), so I plugged that in and it appears to agree with my JACO gauge.  

I noticed that if I left the system on, the reading gradually increased as if the sensor was heating up.   I couldn't detect any warmth by feel, so I decided it wasn't a "burning out" problem, but I only need to take a pressure reading ocassionally (like once per second or so).   The sensor ohms at 5K ohms from power to ground, so at 5V the current is 1 Ma, I added a PNP (driven by one of the digital output pins) switch to turn the sensor on and back off when the reading is complete.   The sensor takes a little less than 20 Ms to stabilize (see waveforms) after powering it up, so I put a 100Ms delay after power up and before I actually read it.  
I let the system run for several hours and the reading doesnot change.  

I kluged up a sketch which read the sensor then corrected the reading and displayed it on a 20x4 LCD.   I have a test board which had a UNO and a 20X4 LCD with a breadboard, which worked great.  

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My little test board.   It has an UNO, a 20x4 LCD and a breadboard with power unit.

Close up of the power switch for the pressure sensor.

Little portable tank with pressure sensor, on the left.

Closer look at the sensor screwed into the test tank.

Scrolling readings withzero tank pressure.

Waveform while measuting tank with 100 PSI.   If power is applied and maintained to the sensor, it's reading appears to increase like the sensor is heating up.   In order to reduce this, I added a transistor to switch on the power to the sensor under control of the Nano.   Top waveform is the power pulse, lower waveform is the sensor's output.   Note: At application of power (5V) Sensor's output jumps to equal power, then back to zero, and finally up to the actual reading.   The sensor's output appears stable after about 20 Ms.

Sensor waveform at 50 PSI.:w

And at zero PSI.