i2cpressureraspberry pisensor
I want to measure negative pressure which is generated by a diaphragm / membrane pump with 0,5 Bar (according specification).
I am not sure if such a sensor as this https://sensing.honeywell.com/HSCDAND001BASA3-amplified-board-mount-pressure-sensors would work? Measuring range is from 0 to 1 bar. But my pump is generating negative pressure which I want to measure. Is this possible?
Can anybody help me please…
If you just need to detect someone sitting on a chair, you just need to connect a pressure-switch or mat to one of the GPIO pins & read the status. There is plenty of info on this on the RaspberryPi forums.
A robustly-sprung push-button switch on one of the legs could also do.
It seems that the sensor is highly non-linear and this is good in our case.
You can try to connect these sensors to the digital inputs of the RaPi, if they have some hysteresis (AFAIK, the GPIO inputs have a hysteresis). The schematic if the following:
simulate this circuit – Schematic created using CircuitLab
The value of R1 is the same as the resistance of the sensor on the threshold point. Determine it experimentally.
The capacitor C1 is to reduce the induced EMI. One approximate value is 100nF but it may vary.
Mount the resistors and capacitors as close to the CPU board as possible. Use shielded cable (low frequency) to connect the sensors. The shield must be the ground wire.
If the EMI are too big, some software processing of the false positives can be made.
If RaPi has no enough inputs (80) you should make some multiplexing. Note, that in this case, some buffers with hysteresis have to be used - 74HC7540 is good choice. You can use 10 of them and connect all outputs together and control the 3-rd state inputs by GPIO outputs. This way with 10 outputs and 8 inputs you can control 80 pressure sensors.
Best Answer
The linked sensor is an absolute pressure sensor.
Which means it is fine to use it, but the value you get might not be quite what you expect it to be.
As it measures the absolute pressure, it will measure against a close to total vacuum, your pump is working against air pressure. So to get the pressure of the pump, you have to store the pressure value before turning the pump on. Then turn the pump on and measure again. The difference between the two values is the pressure (or rather vacuum) your pump is generating.
For example, the current air pressure is 960 mbar. You will get a reading of 960 mbar from the sensor. Then you turn your pump and it will create some vacuum. The reading you get is then say 500 mbar. The vacuum your pump generates is then 960 mbar - 500 mbar = 460 mbar.
There are relative pressure sensors available which are rated for vacuum, which would make the task a bit easier. They are sometimes sold as vacuum sensors. A range would read like -1 to 1 bar or something like that. There you can use just the reading and don't have to calculate something.