Anex (Exercise 2: Barometer – Altimeter )

Why an altimeter / barometer ?

Well a barometer could be very helpful for further projects.
Air planes, submarines, and a lot of other projects that I’ve, which are not related with drones 🙂

Measuring  the pressure we can know the  strength of air ( in this case), if we take the difference between two points, we could see which is the difference of this strength and will be related by the altitude.
We could measure the pressure in liquids two, to know the deep, or other parameters, just is a little question about physic


.- Sensor (MPX4115) : very important to read the data sheet and understand it.
.- Operational amplifiers (lm358) in my case.
.- Resistors, potentiometers
.- Some capacitors

How does it works ?

We have this graph from the data sheet of the MPX4115.
I’ve added two columns were is our range of work.

To see our range values
.- ground = 1013 kPa
.- 1000 m = 900 kPa
(you can use this page to calculate, be careful cause the pressure is related with the weather)

With an analogue sensor we can work by range ,  in the real life between two points we have infinite points 🙂 , so we can adjust our circuit for the range we need.

From the data sheet MPX4115

From the data sheet MPX4115

So we have to calculate the resistors to use the operational amplifiers for our necessities
For higher pressures, for example for submarines I’ll use the MPX5700 ( from 10 kPa to 700 kPa aprox 70 meters underwater)


Well is a very bad video, I know, but is quite difficult to move circuit and record with the other hand.

First the sensor is over my table, and I put on the floor (80 cm lower) and give a value (622)
I take the circuit a move to around 2 meter above the floor and the value is (607)
And move to the floor and finally to the desk.

We have a difference of 15 (pressure on the floor – pressure two meter above)  so It can give us the information about the altitude. By the moment it’s no changed to human units 🙂

And here the video

The sensitivity is higher than the theoretical to obtain values in a really low altitude , but is just a question of  the potentiometer to adjust.
But as much sensitivity the noise is higher, we can try to reduce by electronics and / or software.

The circuit

Altitude based on pressure. Sensor MPX4115

Altitude based on pressure. Sensor MPX4115


Gutting the circuit

I took as the low level the minimum pressure register (870 hPa, I know the circuit is made for 890 hPa it was a mistake that I made) this is made by the divisor resistor.
The pressure sensor has a potentiometer to adjust the values to the range that we need

The circuit has two different power supply (5v and 9 v) the OA there are not ideals so to take advantage of  all the range of the ADC


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