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Selecting the Power Supply

A project log for Solar Powered WiFi Weather Station V3.0

ESP32 based Open Source Weather Station

Debasish DuttaDebasish Dutta 10/07/2021 at 13:550 Comments

If you are planning to install the weather station at a remote location like your farmhouse, you may not get access to the power grid to run the weather station. To run the 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 in the case of the battery, after some days of run, its juice will run out, and it is a really difficult job to go there and charge it. So a solar charging circuit was proposed to use free energy from the sun to charge the battery and to power the ESP32 board.

Here, 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 a battery protection chip or without the protection chip. I will recommend buying a module that has a battery protection chip included.

The 18650 battery outputs 4.2V when fully charged. The battery voltage is further step down to 3.3V by using a low dropout voltage regulator(MCP1700-3302E).

The output from the voltage regulator will power the ESP32 through the 3.3V pin.

Power Supply Circuit:

The operating voltage of the ESP32 is 3.3V whereas the fully charged battery voltage is 4.2V. So we have to step down the battery voltage from 4.2V to 3.3V, which can easily be done by a linear voltage regulator but unfortunately, it is not at all recommended for this project. Because all the linear regulators require an input voltage at least some minimum amount higher than the desired output voltage. That minimum amount is called the dropout voltage. Due to this reason when battery voltage drops to around 3.7V, the linear voltage regulator will not able to maintain the voltage required voltage ( 3.3V ).

The solution to the above problem is to use a low-dropout or LDO regulator. A low-dropout or LDO regulator is a DC linear regulator which can regulate the output voltage even when the supply voltage is very close to the output voltage. Here we will use an MCP1700 LDO for efficiently powering the Circuit.

A ceramic capacitor ( 0.1uF) and an electrolytic capacitor (100uF) are connected in parallel to the GND and Vout pin of the LDO ( MCP1700 -3.3V ) to smooth the voltage peaks.

The output of the MCP1700 is connected to the ESP32 3.3V pin through a slide switch.

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