I'm trying to connect a pressure sensor MPX4144 inside a ballon so that when I pressure the ballon, it does change some color. I tried to hook up the sensor, but I get very small values, should I connect an amplifier to it or what ? I'm sure there is an amplifier inside that sensor, or that sensor can't work for that purpose, like putting it inside a balloon to sense if someone is pressuring or not ?
The pressure in a balloon is not very much above atmospheric pressure. I saw one reference that said it was a little over 2kPa which would give about a 100mV change in the sensor output voltage. If you want to amplify that you can use an op amp circuit, with offset to remove the atmospheric background pressure and gain to amplify the 100mV change.
I tried the circuit, the output of the op-amo is always 3.71v whatever the variable resistor is, and the output of the sensor pressure is 3.91v. What could be wrong ?
I tried the circuit, the output of the op-amo is always 3.71v whatever the variable resistor is, and the output of the sensor pressure is 3.91v. What could be wrong ?
h21,
The MX4115 has an output of approximately 0.2V without any pressure difference, the 100mV change you stated is added to this 0.2V so it could be 0.3V at max pressure.
You should not have 3.9V on the +Vinp pin.
Can you post a picture of your project.?? also measure the voltage output of the MX [ not connected to the LM358] with no pressure and no pressure.?
E.
EDIT:
Mark on this plot image the range you are working with, min and max.
it measures the atomospheric pressure, that's why it gets 3.90v. How can I test then without any pressure ?
The sensor without any connection at all, it gets 3.90V, when connectiong just GND, VS, and check the output
hi,
The ambient air pressure is approx 101kilopascals, which you measure on that sensor, what I need to know is when you apply the pressure equal to the pressure the balloon, what does it measure then.?
In Post #2, Carl said he has a value of approx 2kP above ambient inside an inflated balloon, so how much does the voltage change from outside the balloon to the inside of the balloon.?
Without using the op-amp configuration. The output voltage is 3.95 inside the balloon, and outside is 3.90v. When using the op-amp. output voltage inside balloon is the same without balloon which is 3.90V
Without using the op-amp configuration. The output voltage is 3.95 inside the balloon, and outside is 3.90v. When using the op-amp. output voltage inside balloon is the same without balloon which is 3.90V
hi 21,
Running a few simulations even with +9Vs shows that the MX4115 is not suitable for the project, due to the offset voltage of 3.9V at ambient pressure and the 50mV voltage change inside the balloon.
The ambient pressure can change by a few kP due to the weather.
hi 21,
Exactly what are you trying to do, it sounds interesting, but what is its purpose.?
A Difference amp could be a solution, but what would you use as a reference input.???
A second MX4115 outside the balloon would be required in order to provide the ambient pressure .
That would not work correctly.
By using a fixed 3.9V you are assuming that the outside ambient pressure is approx 101kPascals.
Consider what would happen if the inside pressure was say 103kP and due to changes in weather conditions the ambient pressure changed to say 102kP, that would mean the OPA would only show 1kP differential pressure, not the original 2kP.
Or if the ambient fell to 100Kp, the difference would be 3kP.
When using a toy rubber balloon the size would change to try to compensate for the pressure difference, but a thick walled gymnastic ball may not.