Solar Powered Mini-Weather Station

  • I remember having one of those beginner electronic kits when I was young and I was so excited the day I listened to our local radio station with the crystal radio I built with the kit. Decades later now, I’m finally re-living my childhood with MySensors. It was fun back then and it is again. I’m definitely a noob at this, I’m not an electrical engineer, but I have a knack for adopting the work of others and applying it to my own world. So to start off this project, I first need to thank Hek and all the other more knowledgeable and capable people that have developed what I use. This is really fun.

    Many of the MySensor projects are weather related, and this one is no different. I figured if I can do simple sensoring, I’ll learn the basics necessary to move on to the more advanced technologies. I am so new to this that I had to buy a soldering iron and learn how to use it. Research and practice are all part of this, and to that end I’ve already built my Vera Serial Gateway and my first sensor – a battery powered temperature and humidity sensor that sits in my kitchen. This project is my attempt to extend that knowledge to a mini-weather station that operates outdoors.

    My requirements were simple: 1) Build an inexpensive outdoor weather station, 2) Use the low-power battery features found in the MySensors Arduino libraries, and 3) Integrate it into my Vera home automation environment. I first put a list together of the components I could put into the weather station to comply with my first requirement. The list goes as follows (I’ve been using eBay, usually in lots of 10):

    • Arduino Pro Mini 3.3v 8MHz processor @ $2.50 USD
    • NRF24L01+ Transceiver @ $0.90
    • DHT22 Humidity & Temperature sensor @ $3.50
    • BMP180 Barometric Pressure sensor @ $1.70
    • BH1750FVI Ambient Light Intensity sensor @ $2.10
    • Rain Sensor Module @ $1.30

    The weather station components total $12.00 USD without power and a project box. Humidity was actually the most expensive piece given that the BMP180 also provides temperature. The DHT11 is less costly, but doesn’t really provide the range for an outdoor sensor. I did look at adding some other sensors. For another $10 I could add Ultraviolet sensing, for $25 I could put in a lightning sensor, $45 for wind speed, and even more for wind direction and a rain gauge. All those others would be great to have, but too costly for this project. I might try my hand at building an anemometer to add to this, and I see others are working on rain gauges, but those are projects for another day.

    I then needed power and an enclosure. I could have put them in a large waterproof box ($2.70), a three cell AA battery holder ($0.80), and some DuraRabbit batteries for a year ($3.00). For an additional $6.50, I was ready to go. Oh, did I mention I was lazy? I don’t really want to swap out the batteries every six months (or less), so I decided to splurge and go the solar route.

    Add a 5v solar panel ($3.35) and a 3.7v 1000mAh li-ion battery ($3.75), and some way to charge the battery (Micro USB 5V 1A 18650 Lithium Battery Charger Board With Protection Module @ $0.75) instead, and my total project cost went to $22.55. Of that, over $10 went to the box, the panel and charger, and the battery. Then I found this.


    It’s entitled “16 LED Solar Power Motion Sensor Security Lamp Outdoor Waterproof Light” ( that you can get for $9.00. I now had a $21 weather station ready to be built.

    Taking apart the lamp, I removed the LED panel (worth at least $2.00) and the control board (this has some good stuff on it like a PIR, a light sensor, and the battery charging circuitry, but its use is well beyond my skills), and put them away for another project.


    I took a 5x7cm fiberglass PCB and cut a few notches in the sides so the board would fit within the new project case. Using the mounting screws that held the LED board down, I had a good way to affix the circuit board to the case.


    Next, I laid out how to cram all these components (including the R1 at 1MΩ & R2 [a 3296W potentiometer 500kΩ] resistors for the voltage divider to track battery voltage and the capacitor for the radio) into the enclosure. I ended up with a tight fit, but very manageable.


    One rule I’ve learned is to always breadboard all the components and measure the performance. This is where I check the current being used during the sleep mode and I get to test my preliminary sketch. It is a very good use of my time as I’ve come upon some bad components in what little of this that I’ve done and this is where they can be identified.


    When I started learning the how-to’s of this hobby, I bought all sorts of stuff. One of the first purchases was one of those boxes of 22-gauge wire. The first one was stranded, so then I had to try solid to see if it was any easier to work with. It is, but is still huge compared to what is needed for these low-current projects. I found some old computer cables that had 26-gauge stranded in them. Better, but not what I wanted. Finally I came upon some discussions of wire-wrapping. I now use 30-gauge solid, first installed with a wire-wrapping tool (what a scam and I even found a cheap one for less than $20.)

    I decided to add two additional features after breadboarding the circuit. First, I wanted a reset button that could be reached without taking the case apart. At times I’ve found my sensors need a quick reboot. A switch was added to the underside of the PCB and a hole in the underside of the case will allow me to use a paperclip to do a reset.

    The other feature I added was a jumper that I could use to enable or disable the rain sensor if I chose to at a later date. For some reason it adds a significant load to the circuit. Without the rain sensor enabled, the circuit idles at 270 µA. With it I get 0.98 mA during the gw.sleep command. If I was smart enough, I’m sure I could get that down, but that’s still something to be learned. The underside, as usual, looked like spaghetti.


    After a little bit of solder (I’m actually getting pretty good at that part), I have a fully functional circuit. Since the Li-Ion charging component takes a micro-USB connection, I charged the battery fully and then adjusted the pot to get the AO output to be right at 1023. For this setup my voltmeter showed the battery at 4.15v. I then needed to calibrate the circuit to get to the lower end of the acceptable voltage range. I’ve seen several different numbers for the bottom end of a 3.7v li-ion battery, some down to 2.7v. I chose 3.3v as my lowest acceptable value and proceeded to drain the battery (those LED arrays came in handy after all) down to 3.0v to see what the circuit value came out to be. For my setup, at 3.3v I was getting a value of 800 from pin A0. I updated the sketch so that it would be equal to 0% (hopefully it never gets there.)

    I had one addition to make to the project case. The rain sensor has a board that needs to be exposed to the elements. I drilled a couple of holes in the front end of the case and found some connectors that would work. The hole in the original case for the PIR sensor was a great opening to pass the cable through. The results actually look pretty good, if I can say so myself.


    A couple of last minute touch-ups: two holes in the lens of the light, one for the reset button and one for the pot that adjusts the sensitivity of the rain sensor. I also take off any LEDs on the circuit, even LED13 on the Arduino. Every little bit helps. Does an LED actually illuminate if no one is there to see it? The final product came out nice.


    One last upload of the final sketch. I took all the weather prediction logic out of the pressure sketch to save room for the other components. The SLEEP_TIME parameter is set for once every minute. I also added some lines of code to have the sensor update all measurements once an hour. I really like the ability to see when a measurement was last updated. That’s a nice touch to the MySensors library.

        #include <SPI.h>
        #include <MySensor.h>  
        #include <DHT.h>  
        #include <BH1750.h>
        #include <Wire.h> 
        #include <Adafruit_BMP085.h>
        #define CHILD_ID_HUM 0
        #define CHILD_ID_TEMP 1
        #define CHILD_ID_LIGHT 2
        #define CHILD_ID_BARO 3
        #define CHILD_ID_BTEMP 4
        #define CHILD_ID_RAIN 5
        #define DIGITAL_INPUT_RAIN_SENSOR 3 
        boolean metric = false;
        int altitude = 221; // 741 feet above sealevel
        float lastBmpTemp = -1;
        float lastPressure = -1;
        float lastHum = -1;
        float lastTemp = -1;
        int BATTERY_SENSE_PIN = A0;
        int lastRainValue = -1;
        int lastBatteryPcnt = 0;
        int updateAll = 60;
        int updateCount = 0;
        uint16_t lastLux;
        unsigned long SLEEP_TIME = 60000;
        int batteryBasement = 800;
        float batteryConstant = 100.0 / (1023 - batteryBasement);
        Adafruit_BMP085 bmp = Adafruit_BMP085();
        BH1750 lightSensor;
        DHT dht;
        MySensor gw;
        MyMessage msgHum(CHILD_ID_HUM, V_HUM);
        MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
        MyMessage msgLux(CHILD_ID_LIGHT, V_LIGHT_LEVEL);
        MyMessage msgBtemp(CHILD_ID_BTEMP, V_TEMP);
        MyMessage msgPressure(CHILD_ID_BARO, V_PRESSURE);
        MyMessage msgRain(CHILD_ID_RAIN, V_TRIPPED);
        void setup()  
          gw.sendSketchInfo("Weather Sensor", "1.0");
          gw.present(CHILD_ID_HUM, S_HUM);
          gw.present(CHILD_ID_TEMP, S_TEMP);
          gw.present(CHILD_ID_LIGHT, S_LIGHT_LEVEL);
          gw.present(CHILD_ID_BARO, S_BARO);
          gw.present(CHILD_ID_BTEMP, S_TEMP);
          gw.present(CHILD_ID_RAIN, S_MOTION);
          metric = gw.getConfig().isMetric;
        void loop()      
          updateCount += 1;
          if (updateCount == updateAll) {
            lastTemp = -1;
            lastHum = -1;
            lastLux = -1;
            lastBmpTemp = -1;
            lastPressure = -1;
            lastRainValue = -1;
            lastBatteryPcnt = -1;
            updateCount = 0;
          float temperature = dht.getTemperature();
          if (isnan(temperature)) {
              lastTemp = -1;
          } else if (temperature != lastTemp) {
            lastTemp = temperature;
            if (!metric) {
              temperature = temperature * 1.8 + 32.0;
            gw.send(msgTemp.set(temperature, 1));
          float humidity = dht.getHumidity();
          if (isnan(humidity)) {
              lastHum = -1;
          } else if (humidity != lastHum) {
              lastHum = humidity;
              gw.send(msgHum.set(humidity, 1));
          uint16_t lux = lightSensor.readLightLevel();
          if (lux != lastLux) {
              lastLux = lux;
          float pressure = bmp.readSealevelPressure(altitude) * 0.01;
          float bmptemp = bmp.readTemperature();
          if (!metric) {
            bmptemp = bmptemp * 1.8 + 32.0;
          if (bmptemp != lastBmpTemp) {
            lastBmpTemp = bmptemp;
          if (pressure != lastPressure) {
            gw.send(msgPressure.set(pressure, 0));
            lastPressure = pressure;
          int rainValue = digitalRead(DIGITAL_INPUT_RAIN_SENSOR);
          if (rainValue != lastRainValue) {
            lastRainValue = rainValue;
          int sensorValue = analogRead(BATTERY_SENSE_PIN);
          int batteryPcnt = (sensorValue - batteryBasement) * batteryConstant;
          if (lastBatteryPcnt != batteryPcnt) {
            lastBatteryPcnt = batteryPcnt;

    Then a test to make sure it’s dumping out its results as it should

        sensor started, id 1
        send: 1-1-0-0 s=255,c=0,t=17,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=255,c=3,t=6,pt=1,l=1,st=ok:0
        read: 0-0-1 s=255,c=3,t=6,pt=0,l=1:I
        send: 1-1-0-0 s=255,c=3,t=11,pt=0,l=14,st=ok:Weather Sensor
        send: 1-1-0-0 s=255,c=3,t=12,pt=0,l=3,st=ok:1.0
        send: 1-1-0-0 s=0,c=0,t=7,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=1,c=0,t=6,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=2,c=0,t=16,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=3,c=0,t=8,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=4,c=0,t=6,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=5,c=0,t=1,pt=0,l=5,st=ok:1.4.1
        send: 1-1-0-0 s=1,c=1,t=0,pt=7,l=5,st=ok:80.8
        send: 1-1-0-0 s=0,c=1,t=1,pt=7,l=5,st=ok:28.2
        send: 1-1-0-0 s=2,c=1,t=23,pt=3,l=2,st=ok:83
        send: 1-1-0-0 s=4,c=1,t=0,pt=7,l=5,st=ok:80.6
        send: 1-1-0-0 s=3,c=1,t=4,pt=7,l=5,st=ok:1020
        send: 1-1-0-0 s=5,c=1,t=16,pt=2,l=2,st=ok:0
        send: 1-1-0-0 s=255,c=3,t=0,pt=1,l=1,st=ok:91

    Finally, we then go to Vera and make sure she’s happy.


    This has been a great learning experience for me as it’s my first documented project. I made a bunch of mistakes in between most of the steps you see here. I’ve practiced my soldering techniques for many, many hours. One battery went bye-bye when I didn’t notice the leads had crossed. The smoke was a real good indicator that I’d messed up. I’ve ruined my fair share of components, but I chalk it all up to experience and don’t dwell on them. This hobby is a lot less expensive than golf or fishing, even with my mistakes. I look forward to bigger and better as I continue learn. Thanks again, Hek. This is a hobby that I truly enjoy.

  • Admin

    Very nice @Salmoides. Really like the solar panel box you found och how you transformed it it your own thing!

  • @Salmoides

    I really like the way you express yourself in: "Decades later now, I’m finally re-living my childhood with MySensors. It was fun back then and it is again."

    This exactly describes the way I think about "Mysensors".


  • Admin

    Yeah, but back then we didn't have all these fun, cheap breakout boards. They are like pick and mix sweets for us amateurs. 🙂

  • Hero Member

    @Salmoides Well Done!! I love it!! and to answer your question... Yes,, an LED will illuminate if no one is there to see it.. 🙂

  • What a great project. I'm also a beginner, having a new hobby with my sons, looking back to my own childhood... One question, your luxmeter, is it hidden behind the collector? Does he gets direct sunlight? Does it works with direct sunlight?

    Looking forwards to your next project!


  • @floris, Thank you for your kind words. The luxmeter faces down, so the light is indirectly collected through the diffuser. If I were to build V2.0, I would look into adding a light pipe to provide more direct lighting on the sensor.


  • you are welcome, thank you for sharing! I'm going to use a waterproof box with a transparent cover. did you connect your hum/temp to d4, rain to d3 and lux to a4 and a5? ( i dont have the barometer yet)

  • @floris, Yes, those are the pins I used. The BMP085 is also I2C, using the same pins as the lux sensor.

  • Great, thanks.

  • @floris Thanks for sharing.

    Do you use the battery provided with the solar panel ?


  • @Totche, the original 3v7, 1000mAh lion battery is tucked under the circuit board. You can see the arch of the plastic cover toward the bottom of the picture on the left, just below the DHT22. It is connected to the circuit with the black and red wired connector so it can easily be removed when working with the device.

  • Hi, did you feed the NRF24L01 directly from the 3.7 V battery? The specs are alowing 3.6 V max?!? And you are taking about a maximum output of over 4 V of the battery.
    That sound not healthy for the NRF.

  • @Andreas-Maurer You can connect the NRF24 on the VCC out from the arduino. because he used an arduino nano pro on 3.3 volt. and the arduino can handle voltages from 3.3 to 12 DC.

  • Hi, I have my weatherstation up and running. The only problem is my rainsensor. It's totally not accurate. Do you have the same?


  • @floris, you have to adjust the sensitivity of the rain sensor. I splashed some water on the sensor pad and used a small screwdriver to adjust the potentiometer on the interface board until it triggered to my satisfaction. It took a few iterations to get it to trigger at the level I was looking for.

  • @Salmoides
    How is this sensor performing? I assume it has to be mounted where it can receive direct sunlight for charging the solar panel. Do you have problems with sunlight heating the enclosure and elevating temperature readings? I intercept readings from my neighbor's 433Mhz outdoor sensor and the temperature soars when the sensor is under direct summer sunlight.

  • @Salmoides great thread and project

    Was trying to follow the wiring on the back side of the board to wire my project and was wondering how you wrap the wires around the posts sticking through the board for soldering.
    Also is there a wiring diagram?

  • @5546dug Wire wrapping is done with a wire wrapping tool, it is done in lieu of soldering and can be easily undone or 'unwrapped'. It was very common for prototyping in the past.

  • @Dwalt Thanks for info but the slant I get from you is this is the old way and now it is just plain soldering.
    I also see wire size is an issue.

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