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/index.html | 115 ++++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) create mode 100644 _site/log/fpm-door-lock-lp/index.html (limited to '_site/log/fpm-door-lock-lp/index.html') 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)

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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.

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

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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.

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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.

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

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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.

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

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Commit: +7529094 +| Gerber: gerber.zip

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by W. D. Sadeep Madurange

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© ASCIIMX - 2025

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