The main system components are VL53L0X distance sensor and STM32F042 micro-controller (MCU). This MCU is one of the smallest ARM Cortex-M0 parts with USB, but still comes in hand-solderable TSSOP-20 package.

Since I have used this sensor and a micro-controller from this family before, I had a good idea on how they both work, so the hardware design was relatively straightforward.

I have found STM32CubeMX pin configuration tool to be very helpful while designing hardware using STM32 parts. It allows to enable all required peripherals and visually see which pins are still free.

The biggest hurdle is separate power rail for VL53L0X (recommended operating voltage of 2.8V). It would be tempting to power micro-controller from the same 2.8V rail, but STM32F042's USB is guaranteed to function for at least 3.0V power rail.

While it would probably be fine to power both of them from a single 3.0V rail, I decided to power MCU from 3.3V and sensor from 2.8V.

I2C bus between them is pulled to 2.8V. High logic level for MCU for the pins I'm using is 0.5 * VDD + 0.2 ~= 1.8V which is well below 2.8V at which the I2C bus is pulled to.

I chose the ubiquitous MIC5504 series low-dropout linear regulators because they are cheap and have very low dropout voltage.

The hardware design for revision 1 is finished and Gerber files are sent for production.