Saturday, June 22, 2019

Low cost ported barometer

You may notice that we have been using ported barometer sensors for compatibility with our dynamic pressure sensors. All of the cheap barometric sensors out there are board mounted and do not have ports. But is there a way we can avoid using a "special" part? This is the subject of today's investigation.

I happened to have an Adafruit BMP180 breakout board, which looks like this:

The Bosch BMP180 sensor is obsolete, but its successors are available on similar breakouts from Adafruit and Sparkfun -- and a variety of other sources online -- very easily for about $10 each. To add a port, I decided to design a 3D printed "cap" for the sensor --

This was the 3D printed part, when complete:

I drilled out the side hole to 3/32" cleanly:

I then cut a piece of 3/32" diameter brass tube, cleaned it with alcohol, and inserted it with a drop of CA glue to hold it in place:

The next steps were to add a tiny bead of CA glue around the edge and press the breakout board int0o the tight fit with the 3D printed part, then add 2 self-tapping screws to hold the assembly together:

I then tried blowing into it underwater to see how well sealed it is. It turns out the largest source of leakage is the porosity of the 3D printed parts themselves:

I think that, for barometric pressure measurement, a micro-leak is unlikely to change the measured pressure appreciably, so this is okay. I then put this in a breadboard and ran the Adafruit demo program for the BMP180, and verified that sucking on the tube increases the measured altitude:

The main problem with this setup is that, to solder it to a board, it would get pretty hot and would probably melt the 3D printed parts! So a next version should probably involve soldering the breakout board to a host PCB first, then adding the little 3D printed "cap".

In any case, for $10 plus change, this is a pretty useful way to make a ported sensor! ;)

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