Why is MPX5500DP is giving a reading at the top of the range (78 PSI) when no pressure is applied.

[marccote]

I try to connect an MPX5500DP to an Arduino Mega but it keeps giving me a reading of about 78PSI which correspond to around 5V even nothing is connected to the ports. I was expecting to get something close to 0 in that case. In don't really care about the noise so the sensor is directly connected the Arduino (1 Vout, 2 GRD, 3 Vcc) and do not use capacitors. I use sample sensors. I tried with 2 different sensors with the same result. Can they be damage on arrival? What can cause such behaviour to the sensors?

[reyes]

Hi Marc Cote,

First it’s important to mention that we really recommend to use the capacitors mentioned in Figure 4 of the MPX5500DP datasheet, otherwise we cannot warranty the correct behavior of the device.

The connections are very important, can I ask if you can send me a picture of your connections of the MPX5500DP, I want to confirm that you are connecting pin 1 to Vout, Pin 2 to GND and pin 3 to VCC (the rest of the pins should not be connected). And that you are really connecting positive pressure on port 1 and “negative pressure” on P2. Pressure on P1 should always be greater or equal to P2, otherwise the device can be permanently damaged. 

Now, have you tested the pressure sensor before connecting it to your Arduino? I just want to make sure that the problem you are seen is not related to the Arduino’s ADC or your code to read it.

If you test the MPX5500DP using only its capacitors and Appling GND and VCC, you should be able to measure the output voltage using a voltmeter.

Have a great day,
Jose Reyes

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