i.Farm - Honeywell TruStability® Pressure Sensors

The MIT E-Vent specifies that it wants a differential pressure sensor. In the fine print it mentions that they use a Honeywell sensor.


I spent some time with Doug Hardman, who is an application engineer with Honeywell. Honeywell makes a line of pressure sensors called TruStability® that were specifically designed for this kind of use case.

It took 2 full days to narrow down the combination of part numbers and inventory available immediately. Honeywell can make more any any sensor, but the lead time is 10 weeks.

The key sensor parameters are:

1. When a person inhales, it's 1 to 5 cm in H20.

2. When a person exhales, it's up to 40 cm in H20.

1 PSI = 70.307 cm in H20.

The differential pressure sensor range that we want in Honeywell Terms is:

+/- 1 PSI

+/- 6.8 kPa

+/- 60 millibar

The rest of this boils down to how you want to install it, if you want analog or digital, and what voltage range you need to work with.

Our engineer was concerned about using an analog port on the Arduino for several reasons, so we have opted to go with i2c as our primary interface choice. Based on this, the following quantities of parts were available a couple days ago.

Note: I see some folks specifying regular pressure sensors. This will be a huge problem. You need the difference between the current air pressure in the room and the patient. The air pressure in the room goes up and down with the temperature in the day, and so if you're not using a differential pressure sensor, you're going to hurt somebody.

Note: If we get an in absolute inventory jam, other gauge and abs pressure sensors can be used, but that will take application notes from Honeywell.

Note: These sensors all come with a 2mm hole nipple. From what I've read, most tubing around a patient is 5mm to 7mm, so you'll need an adapter.

Note: Lots of time was spent talking about how these sensors are installed. These are NOT simple sensors you can hit with your solder iron or dunk into the reflow oven without considerable time setting them up. If you aren't prepared to spend considerable time configuring your reflow oven or getting precision tools to solder these parts down, you'll put somebodies life at risk. Find a board shop that reads the installation requirements of these sensors. It's critical.

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