Solar Powered WiFi Weather Station V2.0

The weather station is run by a 18650 Li-Ion battery, so it is very important to monitor its status. The max voltage input to the Wemos board is around 3.2~3.3V but a fully charged 18650 battery voltage is 4.2V. So to measure this voltage we have to step down the voltage by using a voltage divider network.

The Wemos D1 mini already has an internal voltage divider that connects the A0 pin to the ADC of the ESP8266 chip. The voltage divider is made up off 220k (R1) and 100k (R2). So, we have to add an external resistance with the inbuilt 220k resistor to read the battery voltage. By using a 100k resistance we can measure the max voltage of the battery, but taking some margin, a 220k resistor is selected. It is named R1 on the PCB board and located just above the battery holder.

To select the voltage divider resistance values, you can use this online calculator.

You can also read this article on battery voltage monitoring.

The Wemos D1 mini Pro board have an inbuilt ceramic antenna along with provision for connecting an external antenna to improve the range. Before using the external antenna, you have to reroute the antenna signal from the built-in ceramic antenna, to the external socket. This can be done by rotating the small surface mount (0603) Zero Ohm resistor (sometimes called a link).

You can see the above picture, how I have done this.

You can also watch this video made by Alex Eamesto to rotate the zero ohm resistor. Then snap the antenna SMA connector into the Wemos Pro mini antenna slot.

The Weather Station V2.0 board have 5 additional ports to hook up more weather sensors.The following additional sensors can easily hooked up :

1. GY-1145 Sensor: for measuring UV Index

The SI1145 is a sensor with a calibrated UV sensing element that can calculate UV Index. It  can communicate via I2C communication (address 0x60).You can hook up this sensor with I2C port in the board which is located just side to the power switch.

You can read this article to know more about this sensor.

2. HDC1080: for measuring temperature and humidity

The HDC1080 is a digital humidity sensor with integrated temperature sensor that provides excellent measurement accuracy at very low  power. It can also communicate via I2C communication.

You can read this articleto know more about this sensor.

3. DS18B20: for measuring temperature

It can measure temperature with a minimal amount of hardware and wiring. These sensors use a digital protocol to send accurate temperature readings directly to your development board without the need of an analog to digital converter or other extra hardware. It uses one-wire protocol to communicate with microcontroller. It can be hook up in port-P2 in the board which is located on the right side of the Wemos board.

You can read this article to know more about this sensor.

In the earlier days weather parameters like ambient temperature, humidity and barometric pressure were measured with separate analog instruments: thermometer, hygrometer and barometer.But today the market is flooded with cheap and efficient digital sensors that can be used to measure a variety of environmental parameters.The best examples are sensors like DHT11, DHT 22, BMP180, BMP/E280 etc.

In this project we will use BMP280 / BME280 sensor.

BMP 280 :

BMP280 is a sophisticated sensor that very accurately measures barometric pressure and temperature with reasonable accuracy. The BME280 is the next-generation of sensors from Bosch, and is the upgrade to the BMP085/BMP180/BMP183 - with a low altitude noise of 0.25m and the same fast conversion time. The advantage of this sensor is that it can use either I2C or SPI for communication with microcontroller. For simple easy wiring, I will suggest to by I2C version board.

BME280 :

The new BME280 sensor, an environmental sensor with temperature, barometric pressure and humidity.The BME280 is the next-generation of sensors from Bosch, and is the upgrade to the BMP280.This precision sensor from Bosch is the best low-cost sensing solution for measuring humidity with ±3% accuracy, barometric pressure with ±1 hPa absolute accuracy, and temperature with ±1.0°C accuracy. It can be used in both I2C and SPI.

Note : BME280 can measure humidity but BMP280 can't. In market BMP280 is also available by the name of BME280. So be sure whether it is a BMP280 or BME280.

My plan is to deploy the Weather station at a remote place ( my farm house).To run the Weather Station continuously, there must be a continuous power supply otherwise the system will not work .The best way to provide continuous power to the circuit is by using a battery.But after some days the battery juice will run out, and it is really difficult job to go there and charge it. So a solar charging circuit was proposed to user free energy from the sun to charge the batteries and to power the Wemos board.I have used a 18650 Li Ion battery.

The battery is charged from a Solar panel through a TP4056 charging module. The TP4056 module comes with battery protection chip or without the protection chip.I will recommend to buy a module which have battery protection chip included.

About the TP4056 Battery Charger

The TP4056 module is perfect for charging single cell 3.7V 1 Ah or higher LiPo cells. Based around the TP4056 charger IC and DW01 battery protection IC this module will offer 1000 mA charge current then cut off when charging is finished. Furthermore when the battery voltage drops below 2.4V the protection IC will cut off the load to protect the cell from under  voltage. It also protects against over voltage and reverse polarity connection.