Occasionally topping off the battery in a development board that is being used as a smart home sensor is a mild inconvenience. But when that sensor is in a remote location — especially if it is part of a large network of sensor nodes — keeping everything charged can quickly become a nightmare. As an alternative, many such devices are connected to a solar cell to keep the battery charged without manual intervention. The problem with this approach is that it introduces a lot of extra hardware and complexity into the equation.
Andrei Pokotylo developed the Solar Devboard V1 to address this issue. It is equipped with an ESP32 microcontroller and all the other essentials you would expect from a basic development board. But in addition to that, it also has all the circuitry that is required to safely charge a battery from a solar cell right on the main board. That means the Solar Devboard V1 never needs to be recharged — as long as there is enough sunshine, anyway.
Hardware assembly (📷: Narrow Studios)
Rather than choosing Wi-Fi-focused ESP32 variants that are commonly found on maker boards, Pokotylo selected the ESP32-C6. While it is fully capable of Wi-Fi communication, it also has support for Zigbee and Matter-over-Thread, which are much better suited to low-power sensor networks. The board also follows a Raspberry Pi Pico-style footprint, making it compact while still exposing ten GPIO pins for connecting external hardware.
Power management is handled by Texas Instruments’ BQ25186 battery charging IC. Unlike inexpensive charger modules that can struggle with the constantly changing voltage produced by a solar panel, the BQ25186 is designed specifically for this type of application. It accepts solar input voltages up to 18 V, features an extremely low standby current, and includes power-path management that allows the board to operate directly from the solar panel whenever sufficient energy is available. This reduces unnecessary battery cycling and can significantly extend battery life.
The board also includes a USB-C connector for programming, a JST connector for a lithium battery, and a SparkFun Qwiic connector for solderless I2C sensors. Reverse-polarity protection on the solar input helps prevent accidental wiring mistakes from damaging the hardware.
The board was tested outdoors (📷: Narrow Studios)
After designing the schematic and PCB, Pokotylo had the boards fabricated before manually assembling the surface-mount components with solder paste, tweezers, and reflow soldering. Development was not completely without setbacks, however. During testing, the surface-mount USB-C connector was accidentally torn from the PCB. Fortunately, only a ground pad was damaged, allowing the connector to be repaired with a jumper wire.
To verify the design, Pokotylo used the board under less-than-ideal conditions by running ESPHome over standard Wi-Fi instead of the lower-power mesh protocols. With the board waking every ten minutes to transmit data, the battery was depleted within a day because the small solar panel could not replenish the energy quickly enough. Increasing the wake interval to one hour transformed the results. Data collected through Home Assistant showed the battery voltage falling overnight and recovering steadily after the morning sun reached the panel.
It won’t keep a power-hungry application satisfied for long, but if you just need to collect occasional sensor readings, the Solar Devboard V1 could free you from charging batteries. You can buy your own copy of the board from PCBWay.
o