It's assembly time! First off, we're going to affix the tubing to the sensor in order to sip and puff. The port on the LPS33 isn't really meant to have tubing attached directly to it, but if we take care, we can get a surprisingly robust attachment by using a cable tie to keep the tubing in place and sealed against the port. This is definitely an off label use of the sensor port, as it is meant to be sealed against an enclosure by installing an o-ring in the little groove and fitting the port into a precisely sized hole.

sensors_app_note_diagram.png
This diagram from an application note for the LPS33HW shows the ideal use case. We're improvising!

Before we start assembly, you'll want to make sure that the end of your tubing is cut nice and straight. We want the end of the tubing to be flat, at a right angle to tube itself. Having a flat end will allow the tubing to seal properly against the sensor's port and will allow us to get the tubing as close to the circuit board as possible.

You may use flush cutters to cut the end of the tubing nice and straight. If yours are dull, or you don't have any, you can use a nice sharp hobby knife to make a clean cut. Don't saw it, try to make the cut in one stroke.

Next, prepare your cable tie by inserting the thin tip into the rectangular end and close the loop nearly all the way but not all the way. You want to leave room to insert the tubing.

If the cable tie doesn't make a zipping sound as you close it, you may have it backwards. When you are done it should have this shape:

Next, place the cable tie over the assuredly straight end and carefully close it a bit more until the tie is just big enough for the tubing to fit thorough unimpeded.

 

Now we'll scoot the tie up the tubing a teeny bit and place the  very straight end of the tubing over the little sensor port and carefully push the tubing down as close to the circuit board as you can. It may help to twist the tubing back and forth slightly as you go, kinda like turning a screwdriver back and forth.

You probably won't be able to get the tubing all the way against the PCB, but you want to make sure there is enough of the port sticking into the tubing that when you tighten the cable tie, you will squish the tubing against the port, not just squeeze the tubing shut.

Once you've got the tubing as far down as you can, hold the tubing in place with one hand while scooting the cable tie back down the tubing towards the board.

While the cable tie is still relatively loose, you may wish to rotate it around the tubing to make sure that you'll be able to pull it tight without bumping into the STEMMA QT connectors or something else on the board. Cable ties will rotate as you tighten them, so keep that in mind.

 

Using one hand to keep the tube in place, use the other to start tightening the cable tie and get it pretty tight, but not too tight. Remember that this is not how these sensors are meant to be used so we don't want to crank down on it too hard.

When you are done, viewed from the side the tubing should be squished a bit by the cable tie

Give the tubing a little tug (not a yank) and make sure that it doesn't come off. If it does, pull or cut the cable tie off the end of the tubing and try again. Fortunately, small cable ties like these usually come in packs of 100, so you'll have plenty of times to try.

Once you're happy with it, cut the floppy end of the cable tie off with your flush cutters. I highly recommend using flush cutters for this part because diagonal cutters or other tools will often leave a surprisingly sharp nub at the end. I speak from experience :|

Huzzah! You've successfully assembled the business end of your Sip and Puff.

This guide was first published on Feb 17, 2020. It was last updated on Feb 17, 2020.

This page (Assemble the Sensor) was last updated on Mar 26, 2021.

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