Weather Station Display


Hey, so its been a while, there’s been a few projects since the last post, but I haven’t written them up ūüôĄ .

In an effort to stop the projects accumulating in the half-finished pile, I made an effort to take this project that has been sitting on the workbench for ages and put it on display. Its simple enough but I’m pleased with the result.

Ages ago I wrote some code for an HTU21D temperature and humidity sensor. I made an outdoor housing for the sensor and all, and used it for a while, but the display was a bit impractical. Anyway, this time I used a 2 line 20 character VFD (vacuum fluorescent display) I’ve had for years (sitting in the bits and pieces pile) to display the sensor measurements. I’ve always liked the display and now its time to show it off.

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Changing HTU21D Temperature and Humidity Resolution

By default the HTU21D sets the temperature and humidity sensor resolutions are set at their highest. These default values are, humidity = 12bit and temperature = 14bit. This is all well and good for most situations when you are trying to get the best performance from your device. However, a higher resolution comes at the expense of increased measuring time. Consequently, a longer measuring time will increase the current consumption too.

To demonstrate, I’ve tabulated¬†the maximum measuring times for the different sensor resolution modes from the HTU21D_datasheet.

Resolution Humidity Temperature
14bit NA 50ms
13bit NA 25ms
12bit 16ms 13ms
11bit 8ms 7ms
10bit 5ms NA
08bit 3ms NA

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Dew Point Calculation with HTU21D Humidity Sensor

Having both temperature and humidity sensor capabilities in a single package makes the HTU21D an ideal sensor for a home weather station. As such, if you’re a person who is interested in knowing the current weather conditions, you’ll probably¬†want to know what the Dew Point is too. But before we can get carried away, we need to learn how to use an additional library.

Dew Point calculated with HTU21D sensor

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HTU21D Temperature and Humidity Sensor Tutorial Part 2

If you’ve missed out on part 1 of this tutorial, you can catch up here.

If you closely read the¬†HTU21D_datasheet, you’ll realise¬†that the humidity data that you read directly from the HTU21D sensor does not meet the device’s guaranteed humidity accuracy of +-3%. Additionally, the sensor is only optimised to perform in the range of 5-95%RH, the rated accuracy of +-3% only applies between 20-80%RH.

This excerpt from the datasheet shows the device’s range of performance.


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HTU21D Temperature and Humidity Sensor Tutorial Part 1

This tutorial will show you how to interface your Arduino to a HTU21D humidity and temperature sensor and start taking measurements. Once you’ve got the basics, we’ll take a look at configuring the sensor to optimise its performance. What you’ll need:

  • An Arduino or compatible clone
  • A HTU21D temperature sensor. I’ll be using one of these¬†from Adafruit.
  • Jumper wires

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Reading temperature and humidity from a HTU21D sensor with an Arduino

A few days ago,¬†my HTU21D temperature and humidity sensor from Adafruit arrived in the mail. I’m planning to use it for a temperature and humidity display at home.

HTU21D interfaced to an arduino

In one night I managed to start reading temperature and humidity measurements from the sensor using my own code that uses the Arduino Wire library. I wrote my own code instead of using the Adafruit HTU21D library to practice and learn interfacing a micro to an I2C device. All the measurement results are then output to the serial terminal.

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