OLED Graphing Barometer

The first one I made from spare parts. Then I cleaned that up a little. A couple people expressed interest so I figured they'd be good gifts.

I endeavored to reduce costs and soldering. Many CPU boards, barometer breakouts and displays were investigated and some assemblies with code built. I ended up not using the CPU features you'd expect cause of libraries not playing well. If I dove into assembly I could figure it out perhaps, but it is a 32bit ARM CPU. I decided I didn't need to be that good of a designer.

The sensor has a built-in thermometer. The display sequence show a numeric screen first then the graph. Since it is an indoor device I saw no value in graphing the temp. The 1041/977 graph range is very close to the max/min recorded pressures in Seattle (I live in western Washington state near sea level) and works ever so nicely with the 64 pixel y-axis of the OLED.

I thought about battery power, but the OLED uses a bit of power and OLEDs will dim with use so I opted for no battery and a touch to display.

I didn't want to mess with apps, BLE or WiFi mostly for costs ($ and time). I will avoid a phone/PC based solution if a standalone screen is sufficient.

Adafruit P/N 4600 QT Py - SAMD21 Dev Board - STEMMA QT / Qwiic

Adafruit P/N 4494 DPS310 Precision Barometric Pressure / Altitude Sensor - STEMMA QT / Qwiic

Protosupplies P/N DSP-9 display.

Adafruit P/N 4399 STEMMA QT / Qwiic JST SH 4-Pin Cable - 50mm Long

Adafruit P/N 4397 STEMMA QT / Qwiic JST SH 4-pin Cable with Premium Female Sockets - 150mm Long

3D printed stand (https://www.tinkercad.com/things/azZdbGcetmw-barometerv8fasteners)

1200 ohm resistor (value not critical)

(2) 2.3 mm screws

(4) 2.5mm screws, nuts

Acorn nut + 4-40 screw ( most any metal piece can be substituted).

Gather parts.

Print 3D stand. The 3d print isn't too rigorous. 0.35mm nozzle, 0.2mm layer height, 20% infill, PLA. The stl should be rotated so the side is on the print bed (see supplies image). Minimal scaffolding is then needed.

Install the display with the 2.5mm hardware first.

The QT Py board snaps into place. This can be nerve-racking depending on how close your 3D printer is calibrated. I slide the back of the board in then press down on the USB C connector. This snap-in design was lifted from https://learn.adafruit.com/qt-py-snap-fit-case/3d-printing.

The barometer board mounts using 2.3mm screws.

The P/N 4399 cable goes between the QT Py and the barometer board.

The P/N 4397 goes from the barometer board to the display. Pay attention to the order of the display pins! Vendors have various arrangements. The connector pinout and wire colors is described in this guide: https://learn.adafruit.com/introducing-adafruit-stemma-qt?view=all#technical-specs.

The 1200 ohm resistor is soldered into the QT Py dev board A3 pin and connects to the metal touch button.

I thought the 4-40 brass acorn nut made a nice touch button. As you wish.

I'm presuming you can work the Arduino IDE. Compile and upload the barometer_v8.ino file to the QT Py Dev board. You may have to press the dev board reset button twice quickly in succession to get the upload to happen.

You should now be good to go.