The Beetle-C has its own CPU to control the 7 RGB LEDs and 2 motors. This CPU exposes an I2C slave interface on the 8 pin connector (address 0x38). The car needs 2 power rails to operate. The 3.3v line powers the CPU and the 5v line charges the internal 80mAh LiPo battery. This little battery, in turn, powers the motors and LEDs. There’s no charge indicator on the Beetle-C, so I didn’t discover the power rail relationship until draining the internal battery by using the car with only the 3.3v line active.
For this reason, I chose to use a 5v DC-DC boost converter to provide 5v from my LiPo battery. This also makes it easier to power the Nano since the docs say that its VIN line needs at least 5V and connecting the 3.6-4.2v LiPo directly to the Vcc of the Nano might fry it. As far as power efficiency goes, this isn’t ideal, but I didn’t want to make major modifications to the Beetle-C nor the Nano to power them from the LiPo battery. The 3.3v Vcc of the Nano’s internal voltage regulator then powers the 3.3v line of the Beetle-C.
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