From 3b63c5139ca9a34fa79bc2eb132ecfd71897dc7e Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <sadeep@asciimx.com>
Date: Sun, 2 Nov 2025 15:12:54 +0800
Subject: wip: Unix desktop.

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----
-title: My first PCB
-date: 2025-07-14
-author: Wickramage Don Sadeep Madurange
-layout: post
----
-
-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.
-
-<table style="border: none; width: 100%">
-  <tr style="border: none;">
-    <td style="border: none; width: 49.5%; vertical-align: top; text-align: center;">
-      <img src="front_design.jpeg" alt="Design (front)" style="width: 100%">
-      <p>Footprint (front)</p>
-    </td>
-    <td style="border: none; vertical-align: top; text-align: center;">
-      <img src="front.jpeg" alt="PCB (front)" style="width: 100%">
-      <p>PCB (front)</p>
-    </td>
-  </tr>
-  <tr style="border: none;">
-    <td style="border: none; width: 49.5%; vertical-align: top; text-align: center;">
-      <img src="back_design.jpeg" alt="Design (back)" style="width: 100%">
-      <p>Footprint (back)</p>
-    </td>
-    <td style="border: none; vertical-align: top; text-align: center;">
-      <img src="back.jpeg" alt="PCB (back)" style="width: 100%">
-      <p>PCB (back)</p>
-    </td>
-  </tr>
-</table>
-
-The PCBs have two layers. A copper region serves as the ground plane. The 0.3
-mm wide 1 oz/ft<sup>2</sup> 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/ft<sup>2</sup> 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_back.zip), [gerber_front.zip](gerber_front.zip),
-       [source.tar.gz](source.tar.gz)
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