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POCKET WEATHER STATION By Aarav Garg We’re often describing how you can buy and use very low-cost electronic modules. They’re great because they save you a lot of assembly time and soldering work, and they usually cost less than the parts you would need to build them! Here is an excellent beginners’ project that uses five such modules to make something useful – a mini weather station you can carry everywhere with you. I s it hot in here, or just me? That’s a question you don’t have to ask anymore with this Pocket Weather Station. It is a compact device, powered by an Arduino Nano board, that you can carry anywhere, right in your pocket. It displays the current temperature and humidity on its OLED screen. Sure, you may have the local weather report on your phone, but it’s amazing how much local temperatures can vary from those recorded elsewhere in your area. Plus, knowing the indoor temperature and humidity can be pretty helpful, as how hot or cold it ‘feels’ is strongly affected by humidity, not just temperature. Even with moderate temperatures, high humidity can make you sweat more than a more intense dry heat! One reason it’s so portable is beacuse of its integrated, rechargeable 160mAh LiPo battery. It is an excellent project for learning and is also really fun to make. It even comes in handy sometimes! 56 Silicon Chip Sound interesting? Then let’s dive right in! First steps The first thing to do when beginning with any project is gathering the required components. The required components are listed in the Parts List. They are mostly available from online marketplaces like eBay, AliExpress and Amazon. While they are inexpensive, chances are they will come from overseas, so allow a few weeks (or even months) for delivery. By the way, the DHT11 is a smaller, less accurate version of the DHT22 temperature/humidity sensor that we have used in the past and described in the February 2017 issue (siliconchip. com.au/Article/10529). Its small size is useful in a pocket device. As it incorporates both temperature and humidity readings, we only need the one sensor. The other parts are the Arduino board to query it, the display Australia’s electronics magazine to show the readings and the charger to keep the battery topped up. You need a few basic tools to build the Pocket Weather Station: a soldering iron, hot glue gun (or even better, a tube of neutral-cure silicone sealant and a caulking gun) and, if you’re going to make the optional case, a 3D printer. Preparation Now we need to plan the position of all the components inside the enclosure. I wanted to keep the device as thin as possible, so it is actually convenient to carry in a pocket. Thus I spread all the components out and did not go with a layered structure. That would decrease the width and height, but increase the thickness. Fig.1 shows how I stacked the components inside my Pocket Weather Station. I used an Arduino Nano board because of its size, which is perfect for this project. You could also come up with your own method of stacking the components in ways that reduce the siliconchip.com.au ► ► Fig.1: this is how I laid out the components so that they would fit inside a custom-made case. Fig.2: this diagram serves as both the wiring diagram and a form of circuit diagram; it shows all the connections necessary to turn the separate modules into a Weather Station. You don’t need to use the same colour coding as we did, but we strongly advise that you stick to the red/black colours for the power wires, and make sure that black only goes to ground or negative pads, and red to positive pads. Take note that different DHT11 modules may have different pin-outs. size of the device even further! After you have planned your preferred arrangement, refer to Fig.2, the wiring diagram. This shows how all the modules need to be connected. It’s relatively simple, as there are few modules and none of them need to be modified. Wiring it up Before you build the Pocket Weather Station, you might like to watch my YouTube video showing how I assembled it, at https://youtu.be/ ZhOhBuKC80M There are two types of connections to be made: power (red/black wires) and signal (green/orange/yellow wires). The charger board connects to the battery as well as all the other modules, to power them. The only other connections required are for the I2C serial bus between the Arduino Nano and the display and one signal wire from the DHT11 to the Nano, so it can get readings. Start by connecting the battery to the battery charging module. We aren’t connecting any wires to the switch yet, because that has to be done once everything is installed in the case. You can connect the power supply wiring of the Arduino, OLED and DHT11 modules to each other, and the ground back to siliconchip.com.au the charger module; leave the wires for the switch loose for now. Try to keep the wire lengths just long enough to prevent a mess of wires later on. For all the power supply connections, make sure you get the polarity correct, with black wires to the GND pins only and red wires to the positive pins. If you connect them the wrong way around, chances are that some of the modules will be damaged. Also, try to solder everything accurately to prevent any kind of short circuit. It might be a tedious process, but believe me, later on it will feel worth the effort. After you have finished soldering all the components (excluding the switch), it should look something like Fig.3. I am sure we can’t carry it around like this, so clearly we need an enclosure for our Pocket Weather Station to give it that professional look. And the best option that we have here is 3D printing. I don’t have a 3D printer, so I used an online 3D printing service based locally in India (www.iamrapid.com). I uploaded my .stl files to get an instant quote and ordered the parts right away. The enclosure I designed the enclosure in Tinkercad, which is a fantastic CAD software package. It supports all skill levels, so even if you are a beginner, you can still use it. You can download my 3D files (.stl format) from the Silicon Chip website. Australia’s electronics magazine Fig.3: once you have finished wiring nearly all the components together, it should look like this. November 2021  57 The 3D-printed case for the Pocket Weather Station. There are a few 3D printing services around Australia which can process the supplied STL file for you. The enclosure they delivered to me has a great build quality. Chances are you will find a similar local service. Do a web search for “3D printing service” or go to your nearest Jaycar Maker Hub, which offers a 3D printing service (see our June 2020 issue for details; siliconchip.com.au/ Article/14472). You might also find a nearby maker space (see https://wiki. hackerspaces.org/australia). Fortunately, all the cutouts that I had made in the design were in the exact spots I needed them, so I didn’t have to get a second prototype made. Putting it all together Now, we need to place the whole circuit inside the enclosure that we designed earlier and 3D printed. It is vital that all the parts go in their respective cutouts to give the device the much-needed professional look. It is also important that all the components are firmly fixed in their place and do not move inside the enclosure, to ensure proper and smooth functioning of the device. I used hot melt glue to fix the parts inside the enclosure. However, while this is convenient, it can fail if exposed to enough heat (eg, if it’s left exposed in direct sunlight inside a car). For this reason, you could instead use the slightly more permanent neutral cure silicone sealant. It takes longer to cure, but it’s not going to fall apart if it gets hot. As you fix the components in the case, make sure the two USB sockets line up with their access holes around the edges, as you will need to connect to both of them later. Now it is time to add the slide switch in its dedicated slot. We did not connect the switch previously because the switch needs to be inserted into the enclosure from the outside. After putting the switch into its slot, use two small screws to fix it in place. Then connect the two wires to it, one from the Vcc pad of the Arduino board At left is the (nearly) completed project, it just needs the wires soldered to the switch at lower right. Hot melt glue was used to make sure the components were secure. Note that this glue can fail if exposed to enough heat. 58 Silicon Chip Australia’s electronics magazine siliconchip.com.au and one wire from the positive output of the battery charging module. If it has three terminals, make sure to connect those wires to two adjacent terminals. This way, the circuit will be completed with the switch slid to that end. Now we need to complete the enclosure. I used screws to fix the lid in place. I had already made screw holes in the design, so that was easy. Just make sure that the cover is securely in place so it looks professional and is convenient to carry. I have put my logo on the lid design to give it a more aesthetic and customised look. After closing it up, all that’s left is to program the Arduino. Programming We need to upload some code to our Pocket Weather Station. Without code in the Arduino, our device is just a plastic box with no functionality. First, download my Arduino sketch from the Silicon Chip website. It is a zipped directory containing a file with a .ino file extension. Unzip the package, install the latest Arduino IDE (integrated development environment) and open the .ino file. If you wish to, you can get your hands dirty and write the code yourself. But if you’re a beginner (and even if you aren’t), it’s best to start with my version since we know it works. You can always modify it once you get it working. See the panel if you are interested in how the software works; that information could come in handy if you plan to make changes to it. Once you have the code open in the Arduino IDE, plug the Arduino Nano into your computer’s USB port (don’t plug into the USB charger port as it does not pass data to the Arduino). Then press CTRL+U (or select Sketch → Upload) to compile the code and load it into the Arduino. Check the output at the bottom of the window for error messages. Compilation takes a few seconds, and if it finds a problem with your code, it will tell you there. Otherwise, you should get an “Upload successful” message, and your Pocket Weather Station will be fully operational. Don’t forget to charge the cell (via the other USB port) so it is ready for use. The cell charge lasts quite a long time, so you will barely need to charge it. Now, you can proudly carry the device wherever you go and flaunt siliconchip.com.au Parts List – Pocket Weather Station 1 Arduino Nano or equivalent board 1 USB cable, to suit the Nano 1 DHT11 temperature sensor module 1 0.96in OLED screen with I2C interface and SSD1306 controller 1 TP4056 li-ion battery charging module (Silicon Chip Cat SC4305) 1 small 1S LiPo cell (eg, 160mAh) 1 slide switch 1 set of 3D printed case pieces (optional) 6 small self-tapping screws (two for mounting the switch, four for the lid) various lengths of light-duty hookup wire How the software works The software for this project is relatively simple. Don’t be daunted by the length of the code; half of it is simply the bitmap graphics for the splash screen! The first few lines include all the libraries we will need: the graphics libraries, humidity/temperature sensor interface library, fonts etc. It then creates the object to communicate with the DHT temperature sensor using pin D4 and another object to drive the screen with a resolution of 128x64 pixels. Following this is the logo bitmap, then below that the main body of the code, which comprises three functions: setup() (for initialisation), loop() (the part which runs continuously after setup) and testdrawbitmap(), which draws the logo on the screen. The setup() function starts the serial port and DHT temperature sensor communications, then initialises the display, draws the logo and pauses for one second. Once the setup() routine has finished (ie, after that one-second delay with the logo on the screen), the loop() function is repeatedly called as long as the unit has power. Each time the loop() function runs, it starts by acquiring temperature and humidity readings from the DHT11 sensor, then prints that data to the serial console. It follows by clearing the screen, then printing the same information on that screen, including what the temperature ‘feels like’ based on the combination of temperature and humidity. It then pauses for two seconds before the process repeats. As this code is all relatively straightforward, you should be able to modify it (eg, to change the way the readings are displayed on the screen) should you wish to do so. your creation (or maybe actually use it as a weather station). Troubleshooting If you are here, that probably means that you have built the project, and it didn’t work. Don’t worry, you will get it working and you will learn a lot from troubleshooting it: 1. The OLED screen is blank You might have damaged your OLED display due to an incorrect connection, but more likely, you haven’t connected the signal wires properly, so re-check them. There might also be an error in your code (for example, if you have forgotten to initialise the display). Try using my code first as we know it works, then modify it from there once you it working. Australia’s electronics magazine 2. All readings are “NA” This will happen if it can’t communicate with the temperature sensor. You might have a problem with the connection between the temperature sensor to the Arduino board. Just re-check the connections. If they are correct, you might have a problem with the sensor itself; try replacing it. 3. It works when the USB cable is plugged in, but not from the battery If this happens, there is a problem with your battery or perhaps the connections between the battery and the rest of the circuit. Links This project on the Instructables website: siliconchip.com.au/link/ab9r This project on the HackSpace website: siliconchip.com.au/link/ab9s SC November 2021  59