From e04ce2ab6ca82d0014bec8b217215f35b436ff25 Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Fri, 26 Dec 2025 16:53:45 +0800 Subject: FPM lock journal style. --- _site/log/fpm-door-lock-lp/breadboard.jpg | Bin 0 -> 46771 bytes _site/log/fpm-door-lock-lp/footprint.png | Bin 0 -> 198127 bytes _site/log/fpm-door-lock-lp/gerber.zip | Bin 0 -> 89431 bytes _site/log/fpm-door-lock-lp/index.html | 115 ++++++++++++++++++ _site/log/fpm-door-lock-lp/pcb.jpg | Bin 0 -> 68237 bytes _site/log/fpm-door-lock-lp/pcb1.jpg | Bin 0 -> 37068 bytes _site/log/fpm-door-lock-lp/source.tar.gz | Bin 0 -> 29473 bytes _site/log/fpm-door-lock-lp/thumb_sm.jpg | Bin 0 -> 18380 bytes _site/log/fpm-door-lock-lp/video.mp4 | Bin 0 -> 13264594 bytes _site/log/fpm-door-lock-rf/back.jpeg | Bin 0 -> 34023 bytes _site/log/fpm-door-lock-rf/back_design.jpeg | Bin 0 -> 31946 bytes _site/log/fpm-door-lock-rf/front.jpeg | Bin 0 -> 28997 bytes _site/log/fpm-door-lock-rf/front_design.jpeg | Bin 0 -> 32174 bytes 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file mode 100644 index 0000000..5511bf1 Binary files /dev/null and b/_site/log/fpm-door-lock-lp/footprint.png differ diff --git a/_site/log/fpm-door-lock-lp/gerber.zip b/_site/log/fpm-door-lock-lp/gerber.zip new file mode 100644 index 0000000..19a9d19 Binary files /dev/null and b/_site/log/fpm-door-lock-lp/gerber.zip differ diff --git a/_site/log/fpm-door-lock-lp/index.html b/_site/log/fpm-door-lock-lp/index.html new file mode 100644 index 0000000..76715d7 --- /dev/null +++ b/_site/log/fpm-door-lock-lp/index.html @@ -0,0 +1,115 @@ + + + + + Fingerprint door lock (LP) + + + + + Fingerprint door lock (LP) + + + + + + + + + + + + + +
+
+
+

FINGERPRINT DOOR LOCK (LP)

+
18 AUGUST 2025
+
+

Second iteration of the RF door lock. Old version worked +but drew too much quiescent current. Sensor and servo pulled 13.8mA and 4.6mA +idle. Linear regulators were a disaster. Battery didn’t last 24 hours.

+ + + +

Redesigned the PCB completely. Tossed the RF modules and the second MCU. +Connected R503 sensor directly to the ATmega328P. Sensor now mounts on door +exterior, servo attaches to interior knob, MCU stays on the back to prevent +tampering.

+ + + + + + + + + +
+ PCB + + Design +
+ PCB footprint +
+ +

PCB specs: 2-layer, 1oz copper, 0.3mm traces (1mm for power and servo). Ground +plane on bottom layer.

+ +

Solved idle power draw with MOSFETs. 2N7000 and NDP6020P cut power to sensor +and servo before deep sleep. Through-hole MOSFETs that switch at 3.3V are +getting harder to find. NDP6020P already obsolete.

+ +

Replaced linear regulators with MP1584EN DC-DC buck converters. No RF, noise +isn’t a big concern. Buck’s pin breakout not great–wouldn’t fit most +commercial dev boards.

+ +

Squeezed more power savings from the MCU by running it at 3.3V/8MHz. Combined +with buck converters: 56% total power savings.

+ +

Wake sequence: MCU activates sensor MOSFET, unlocks sensor over UART, scans and +matches fingerprint. Match triggers blue LED, servo MOSFET, PWM signal to +unlock. No match triggers red LED. MOSFETs off, back to sleep.

+ +

Total power savings: 99.9% (30.6mA → 2.9μA). Verdict: Fixed.

+ +

Commit: +7529094 +| Gerber: gerber.zip

+
+

by W. D. Sadeep Madurange

+
+
+
+ +
+
+
+

© ASCIIMX - 2025

+
+
+
+ + + + diff --git a/_site/log/fpm-door-lock-lp/pcb.jpg b/_site/log/fpm-door-lock-lp/pcb.jpg new file mode 100644 index 0000000..fbd800b Binary files /dev/null and b/_site/log/fpm-door-lock-lp/pcb.jpg differ diff --git a/_site/log/fpm-door-lock-lp/pcb1.jpg b/_site/log/fpm-door-lock-lp/pcb1.jpg new file mode 100644 index 0000000..367187d Binary files /dev/null and b/_site/log/fpm-door-lock-lp/pcb1.jpg differ diff --git a/_site/log/fpm-door-lock-lp/source.tar.gz b/_site/log/fpm-door-lock-lp/source.tar.gz new file mode 100644 index 0000000..ef23422 Binary files /dev/null and b/_site/log/fpm-door-lock-lp/source.tar.gz differ diff --git a/_site/log/fpm-door-lock-lp/thumb_sm.jpg b/_site/log/fpm-door-lock-lp/thumb_sm.jpg new file mode 100644 index 0000000..a8fa534 Binary files /dev/null and b/_site/log/fpm-door-lock-lp/thumb_sm.jpg differ diff --git a/_site/log/fpm-door-lock-lp/video.mp4 b/_site/log/fpm-door-lock-lp/video.mp4 new file mode 100644 index 0000000..a907a9b Binary files /dev/null and b/_site/log/fpm-door-lock-lp/video.mp4 differ diff --git a/_site/log/fpm-door-lock-rf/back.jpeg b/_site/log/fpm-door-lock-rf/back.jpeg new file mode 100644 index 0000000..f458e69 Binary files /dev/null and b/_site/log/fpm-door-lock-rf/back.jpeg differ diff --git a/_site/log/fpm-door-lock-rf/back_design.jpeg b/_site/log/fpm-door-lock-rf/back_design.jpeg new file mode 100644 index 0000000..b6c0f5d Binary files /dev/null and b/_site/log/fpm-door-lock-rf/back_design.jpeg differ diff --git a/_site/log/fpm-door-lock-rf/front.jpeg b/_site/log/fpm-door-lock-rf/front.jpeg new file mode 100644 index 0000000..2b2931f Binary files /dev/null and b/_site/log/fpm-door-lock-rf/front.jpeg differ diff --git a/_site/log/fpm-door-lock-rf/front_design.jpeg b/_site/log/fpm-door-lock-rf/front_design.jpeg new file mode 100644 index 0000000..f81f09c Binary files /dev/null and b/_site/log/fpm-door-lock-rf/front_design.jpeg differ diff --git a/_site/log/fpm-door-lock-rf/gerber_back.zip b/_site/log/fpm-door-lock-rf/gerber_back.zip new file mode 100644 index 0000000..26659ad Binary files /dev/null and b/_site/log/fpm-door-lock-rf/gerber_back.zip differ diff --git a/_site/log/fpm-door-lock-rf/gerber_front.zip b/_site/log/fpm-door-lock-rf/gerber_front.zip new file mode 100644 index 0000000..864334e Binary files /dev/null and b/_site/log/fpm-door-lock-rf/gerber_front.zip differ diff --git a/_site/log/fpm-door-lock-rf/index.html b/_site/log/fpm-door-lock-rf/index.html new file mode 100644 index 0000000..c12d808 --- /dev/null +++ b/_site/log/fpm-door-lock-rf/index.html @@ -0,0 +1,120 @@ + + + + + Fingerprint door lock (RF) + + + + + Fingerprint door lock (RF) + + + + + + + + + + + + + +
+
+
+

FINGERPRINT DOOR LOCK (RF)

+
26 APRIL 2025
+
+

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.

+ + + + + + + + + + +
+ Design (front) +

Footprint (front)

+ 		+ PCB (front) +

PCB (front)

+
+ Design (back) +

Footprint (back)

+ 		+ PCB (back) +

PCB (back)

+
+ +

The PCBs have two layers. A copper region serves as the ground plane. The 0.3mm +wide 1oz/ft2 copper traces can carry up to 500mA (the tracks +connecting the power source and the linear regulators have a width of 0.5mm). +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 13.8mA (3.3V) and 4.6mA +(5V) respectively, as long as they are connected to the power supply.

+ +

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

+
+

by W. D. Sadeep Madurange

+
+
+
+ +
+
+
+

© ASCIIMX - 2025

+
+
+
+ + + + diff --git a/_site/log/fpm-door-lock-rf/source.tar.gz b/_site/log/fpm-door-lock-rf/source.tar.gz new file mode 100644 index 0000000..c31aa22 Binary files /dev/null and b/_site/log/fpm-door-lock-rf/source.tar.gz differ diff --git a/_site/log/fpm-door-lock-rf/thumb_sm.jpeg b/_site/log/fpm-door-lock-rf/thumb_sm.jpeg new file mode 100644 index 0000000..c275b12 Binary files /dev/null and b/_site/log/fpm-door-lock-rf/thumb_sm.jpeg differ diff --git a/_site/log/fpm-door-lock/breadboard.jpg b/_site/log/fpm-door-lock/breadboard.jpg deleted file mode 100644 index 2bf47a9..0000000 Binary files a/_site/log/fpm-door-lock/breadboard.jpg and /dev/null differ diff --git a/_site/log/fpm-door-lock/footprint.png b/_site/log/fpm-door-lock/footprint.png deleted file mode 100644 index 5511bf1..0000000 Binary files a/_site/log/fpm-door-lock/footprint.png and /dev/null differ diff --git a/_site/log/fpm-door-lock/gerber.zip b/_site/log/fpm-door-lock/gerber.zip deleted file mode 100644 index 19a9d19..0000000 Binary files a/_site/log/fpm-door-lock/gerber.zip and /dev/null differ diff --git a/_site/log/fpm-door-lock/index.html b/_site/log/fpm-door-lock/index.html deleted file mode 100644 index 1460053..0000000 --- a/_site/log/fpm-door-lock/index.html +++ /dev/null @@ -1,168 +0,0 @@ - - - - - Fingerprint door lock - - - - - Fingerprint door lock - - - - - - - - - - - - - -
-
-
-

FINGERPRINT DOOR LOCK

-
18 AUGUST 2025
-
-

This project features a fingerprint door lock powered by an ATmega328P -microcontroller.

- - - -

Overview

- -

The lock comprises three subsystems: the ATmega328P microcontroller, an R503 -fingerprint sensor, and an FS5106B high-torque servo. The sensor mounted on the -front surface of the door enables users to unlock it from the outside. The -servo is attached to the interior door knob. The MCU must be installed at the -back of the door to prevent unauthorized users from tampering with it.

- -

When no one is interacting with the lock, the MCU is in deep sleep. The sensor -and the servo each draw 13.8mA and 4.6mA of quiescent currents. To prevent this -idle current draw, the MCU employs MOSFETs to cut off power to them before -entering deep sleep. Doing so is crucial for conserving the battery.

- -

Without power, the sensor remains in a low-power state, drawing approximately -2.9μA through a separate power rail. When a finger comes into contact with the -sensor, the sensor triggers a pin change interrupt, waking up the MCU. The MCU -activates a MOSFET, which in turn activates the sensor. Over UART, the MCU -unlocks the sensor and issues commands to scan and match the fingerprint.

- -

If the fingerprint matches an enrolled fingerprint, the MCU activates the blue -LED on the sensor, turns on the MOSFET connected to the servo, and sends a PWM -signal to the servo to unlock the door. Otherwise, the MCU activates the red -LED on the sensor. Finally, the MCU deactivates the MOSFETS and goes back to -sleep.

- -

Embedded software

- -

The embedded software, written in C, includes a driver for the sensor, servo -control routines, and a battery monitoring system.

- -

In addition to controlling the sensor and the servo, the program strives to -maintain precise control over the microcontroller’s sleep modes, as well as -when the peripherals are activated and for how long they remain active. I -thoroughly enjoyed writing the embedded software. There’s something magical -about being able to alter the physical world around you by uttering a few lines -of C code.

- -

The source code of the project, which includes a driver for the R503 -fingerprint sensor module, is enclosed in the tarball linked at the end of the -page.

- -

The PCB

- -

For this project, I designed a custom PCB and had it fabricated by JLCPCB. Like -the software, the circuit is primarily concerned with optimizing power -consumption and extending battery life.

- - - - - - - - - -
- PCB - - Design -
- PCB footprint -
- -

Consequently, the principal components of the circuit are the 2N7000 and -NDP6020P field-effect transistors. They switch power electronically to the -servo and the fingerprint sensor, the two most power-hungry parts of the -circuit. The two MP1584EN buck converters play an axial role in efficiently -regulating power to the MCU and the sensor.

- -

The ATmega328P typically operates at 5V with a 16MHz crystal oscillator. To -further reduce power consumption, I modified the ATmega328P’s fuses to run at -3.3V with an 8MHz crystal oscillator.

- -

The bottom right area of the PCB isolates the power supply of the servo from -the rest of the circuit. This shields components such as the MCU from the -servo’s high current draw, which can exceed 1A. The IN4007 diode in slot U2 -serves as a flyback diode, protecting the MOSFET from reverse currents -generated by the servo.

- -

Lastly, the 56kΩ and 10kΩ resistors in slots R10 and R11 form a voltage divider -circuit. Its output is fed to the ADC of the MCU, which measures the supply -voltage by comparing it to the internal bandgap reference voltage.

- -

Epilogue

- -

This project began nearly a year ago when I attempted to unlock our door -wirelessly by writing to the UART ports of two MCUs connected to inexpensive -433MHz RF transceivers. Although I failed, it led me down a rabbit hole of RF -communications, MOSFETs, PCB design, and low-power circuits.

- -

During the project, I reinvented the wheel many times. I implemented a -low-level network stack using only RF modules and an 8-bit microcontroller, -designed my first PCB, and developed drivers from scratch. The project was far -from a smooth sail. Bad electrical connections, soldering and desoldering, and -the heartache of purchasing the wrong parts were routine. It was a long but -rewarding journey from the messy breadboard to the shiny PCB.

- -

Files: source.tar.gz, gerber.zip

-
-

by W. D. Sadeep Madurange

-
-
-
- -
-
-
-

© ASCIIMX - 2025

-
-
-
- - - - diff --git a/_site/log/fpm-door-lock/pcb.jpg b/_site/log/fpm-door-lock/pcb.jpg deleted file mode 100644 index fbd800b..0000000 Binary files a/_site/log/fpm-door-lock/pcb.jpg and /dev/null differ diff --git a/_site/log/fpm-door-lock/pcb1.jpg b/_site/log/fpm-door-lock/pcb1.jpg deleted file mode 100644 index 367187d..0000000 Binary files a/_site/log/fpm-door-lock/pcb1.jpg and /dev/null differ diff --git a/_site/log/fpm-door-lock/source.tar.gz b/_site/log/fpm-door-lock/source.tar.gz deleted file mode 100644 index ef23422..0000000 Binary files a/_site/log/fpm-door-lock/source.tar.gz and /dev/null differ diff --git a/_site/log/fpm-door-lock/thumb_sm.jpg b/_site/log/fpm-door-lock/thumb_sm.jpg deleted file mode 100644 index a8fa534..0000000 Binary files a/_site/log/fpm-door-lock/thumb_sm.jpg and /dev/null differ diff --git a/_site/log/fpm-door-lock/video.mp4 b/_site/log/fpm-door-lock/video.mp4 deleted file mode 100644 index a907a9b..0000000 Binary files a/_site/log/fpm-door-lock/video.mp4 and /dev/null differ diff --git a/_site/log/index.html b/_site/log/index.html index 8074ae3..bcc001e 100644 --- a/_site/log/index.html +++ b/_site/log/index.html @@ -59,7 +59,7 @@ - Fingerprint door lock + Fingerprint door lock (LP) @@ -98,7 +98,7 @@ - My first PCB + Fingerprint door lock (RF) diff --git a/_site/log/matrix-digital-rain/index.html b/_site/log/matrix-digital-rain/index.html index f254ed2..8383776 100644 --- a/_site/log/matrix-digital-rain/index.html +++ b/_site/log/matrix-digital-rain/index.html @@ -54,45 +54,48 @@ than it needed to be.

Moved phosphor decay into the 4th byte of the RGB union–should’ve done this -in 2022. What was I thinking.

+in 2022; What was I thinking.

Keeping the RGB union despite portability concerns. All my systems are little-endian and the code is cleaner this way.

Fixed Unicode by introducing a charset array. UNICODE(min, max) packs Unicode -ranges into uint64–low four bytes for start, high four bytes for end. +ranges into uint64: low four bytes for start, high four bytes for end. insert_code() unpacks a random block and picks a character from it:

-
static uint64_t glyphs[] = {
+
#define UNICODE(min, max)  (((uint64_t)max << 32) | min)
+
+static uint64_t glyphs[] = {
     UNICODE(0x0021, 0x007E), /* ASCII */
     UNICODE(0xFF65, 0xFF9F), /* Half-width Katakana */
 };
-

-
-
Full-width Katakana breaks column alignment. Stick to half-width
-(U+FF61-U+FF9F) range. Compile with -DNOKANA to disable Katakana altogether.

 
-
blend() simulates phosphor decay by eroding RGB channels toward
-background color:

-
-
static inline void blend(matrix *mat, size_t row, size_t col)
+static inline void insert_code(matrix *mat,
+    size_t row, size_t col) 
 {
-    unsigned char *color = mat->rgb[index(mat, row, col)].color;
-    color[R] = color[R] - (color[R] - RGB_BG_RED) / DECAY_MPLIER;
-    color[G] = color[G] - (color[G] - RGB_BG_GRN) / DECAY_MPLIER;
-    color[B] = color[B] - (color[B] - RGB_BG_BLU) / DECAY_MPLIER;
+    uint64_t blk;
+    uint32_t min, max;
+
+    blk = glyphs[(rand() % glyphlen)];
+    min = (uint32_t)blk;
+    max = (uint32_t)(blk >> 32);
+    mat->code[index(mat, row, col)] = rand() % (max - min) + min;
 }
 

 
-
That’s still good. Leaving it alone.

+
Full-width Katakana breaks column alignment. Stick to half-width
+(U+FF61-U+FF9F) range. Compile with -DNOKANA to disable Katakana altogether.

+
+
blend() is still good. Leaving it alone.

 
 
Tossed license and automake cruft. Just cc -O3 main.c -o matrix now. Don’t
 need the ceremony.

 
-
Runs at 2-3% CPU on OpenBSD (T490). No regressions. Fans are quiet.

+
Runs at 2-3% CPU on OpenBSD (T490). No cause to measure performance more
+precisely. No regressions. Fans are quiet.

 
 
Commit:
-03f8d87

+69a888a

by W. D. Sadeep Madurange

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-
-
-

MY FIRST PCB

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26 APRIL 2025
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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.

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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.

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- Design (front) -

Footprint (front)

- 		- PCB (front) -

PCB (front)

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- Design (back) -

Footprint (back)

- 		- PCB (back) -

PCB (back)

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

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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 13.8mA (3.3V) and 4.6mA -(5V) respectively, as long as they are connected to the power supply.

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

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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.

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

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by W. D. Sadeep Madurange

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© ASCIIMX - 2025

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