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Barometer

Aug 23, 2023 - 1 minute read
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Github link: https://github.com/bigcrimping/barometer/

Barometer

A reimagining of a classic barometer using a BMP280 pressure sensor

The displays are both Dowty aircraft magnetic indicators which are similar to split-flap displays classically used in train stations

barometer

The display can show high/low/normal pressure and up/down arrows + “auto”. The relays are overkill (the power supply is 28v and the displays when active take ~30mA) but I had them to hand.

The classical logic with a barometer is roughly:

  1. Low pressure means bad weather
  2. High pressure means good weather
  3. Constant pressure usually means good weather
  4. Rising air pressure is good
  5. Lowering air pressure is bad

Project Code

The code is here: https://github.com/bigcrimping/barometer/tree/main/code/pressure_meter

Fairly basic setup using the driver “BMx280MI” from Gregor Christandl, the code measures the pressure every 10 minutes and adds it to a circular buffer and uses the average to determine if the pressure is rising or falling.

Wiring

The wiring is as below.

PRESSURE_NORMAL is on pin 2 PRESSURE_HIGH is on pin 3 ARROW_UP is on pin 4 ARROW_DOWN is on pin 5 I2C SDA is on D18 and SCL is D19

wiring

Mechanical Files

Mech files are here: https://github.com/bigcrimping/barometer/tree/main/mechanical

3d

All mounting holes are M3 brass inserts with M3 x 7mm

Fixing required

6 x M3 brass inserts

6 x M3x7mm cap head bolts