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 9 files changed, 115 insertions(+) create mode 100644 _site/log/fpm-door-lock-lp/breadboard.jpg create mode 100644 _site/log/fpm-door-lock-lp/footprint.png create mode 100644 _site/log/fpm-door-lock-lp/gerber.zip create mode 100644 _site/log/fpm-door-lock-lp/index.html create mode 100644 _site/log/fpm-door-lock-lp/pcb.jpg create mode 100644 _site/log/fpm-door-lock-lp/pcb1.jpg create mode 100644 _site/log/fpm-door-lock-lp/source.tar.gz create mode 100644 _site/log/fpm-door-lock-lp/thumb_sm.jpg create mode 100644 _site/log/fpm-door-lock-lp/video.mp4 (limited to '_site/log/fpm-door-lock-lp') diff --git a/_site/log/fpm-door-lock-lp/breadboard.jpg b/_site/log/fpm-door-lock-lp/breadboard.jpg new file mode 100644 index 0000000..2bf47a9 Binary files /dev/null and b/_site/log/fpm-door-lock-lp/breadboard.jpg differ diff --git a/_site/log/fpm-door-lock-lp/footprint.png b/_site/log/fpm-door-lock-lp/footprint.png new 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) + + + + + + + + + + + + + +
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FINGERPRINT DOOR LOCK (LP)

+
18 AUGUST 2025
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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

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by W. D. Sadeep Madurange

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© ASCIIMX - 2025

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