nRF52832 BLE Node
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The nRF52832 BLE Node based on nRF52832, integrates GPIO, PWM, IIC, analog inputs, PWM, timers, etc all in one board. Leaving out the extra microcontroller means the price, complexity, and power-usage are all lower/better. It allows you to run code directly on the nRF52832, straight from the Arduino IDE as you would with any other MCU or Arduino compatible device.
It is a built-in USB and battery charging.