In 2023, I started tinkering with DIY electronics as a hobby. Until now, I’ve been using development boards like the Arduino Uno and ESP-32-WROOM so that I can focus on the software. Recently, I decided to step outside of my comfort zone and design a PCB from scratch for a door lock I’m working on.

The lock comprises two subsystems: a fingerprint sensor in front of the door and a servo connected to the physical lock behind the door. The fingerprint sensor authenticates the person and signals the servo behind the door to unlock the door over an encrypted RF channel.

Footprint (front)	PCB (front)
Footprint (back)	PCB (back)

The PCBs have two layers. A copper region serves as the ground plane. The 0.3 mm wide 1 oz/ft² copper traces can carry up to 500 mA (the tracks connecting the power source and the linear regulators have a width of 0.5 mm). Both subsystems were functional. I was able to control the servo reliably using the fingerprint sensor.

The designs aren’t without flaws, however. The main shortcoming of the circuits is that they draw significant amounts of quiescent currents despite employing sleep modes. The linear regulators were a poor choice as they dissipate too much heat. The fingerprint sensor and the servo draw 13.8 mA (3.3 V) and 4.6 mA (5 V) respectively, as long as they are connected to the power supply.

Although the circuit didn’t draw more than 200 mA without a load, the servo under load could draw up to 600 mA. I’m sailing too close to the wind with 0.3 mm copper traces. Instead, 0.4 mm wide 2 oz/ft² traces would have been safer.

I’m working on improving the design to reduce idle current consumption and extend the battery life. Despite its deficiencies, this was my first PCB design, and I’m glad that it worked as well as it did. Custom PCB design marks an important milestone in my DIY electronics journey.

Files: gerber_back.zip, gerber_front.zip, source.tar.gz