From 7ea27406fbaa22e4b077d8614cd17f2729d956a0 Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Fri, 24 Apr 2026 11:56:18 +0800 Subject: Minor improvements to LP lock to make it more like a journal entry. --- _log/fpm-door-lock-lp.md | 34 +++++++++++++++++----------------- 1 file changed, 17 insertions(+), 17 deletions(-) (limited to '_log/fpm-door-lock-lp.md') diff --git a/_log/fpm-door-lock-lp.md b/_log/fpm-door-lock-lp.md index b846797..10b452c 100644 --- a/_log/fpm-door-lock-lp.md +++ b/_log/fpm-door-lock-lp.md @@ -1,23 +1,23 @@ --- -title: Fingerprint door lock (LP) +title: Redesigned fingerprint door lock for LP date: 2025-08-18 layout: post project: true thumbnail: thumb_sm.jpg --- -Second iteration of the [fingerprint door lock](../fpm-door-lock-rf). 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. +Second iteration of the [lock](../fpm-door-lock-rf). The 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 RF modules and the second MCU. Connected -R503 directly to the ATmega328P. Sensor now mounts on door exterior, servo -attaches to interior knob, MCU stays on the back to prevent tampering. +Redesigned the PCB completely. Tossed the RF modules and the second MCU. +Connected the R503 sensor directly to the ATmega328P. Sensor now mounts on the +door exterior, servo attaches to the interior knob, and the MCU stays on the +back to prevent tampering. @@ -36,18 +36,18 @@ attaches to interior knob, MCU stays on the back to prevent tampering.
PCB specs: 2-layer, 1oz copper, 0.3mm traces (1mm for power and servo). Ground -plane on bottom layer. +plane on the 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. +Solved idle power draw with MOSFETs. 2N7000 and NDP6020P cut power to the +sensor and the servo before deep sleep. Through-hole MOSFETs that switch at +3.3V are getting harder to find. NDP6020P is already obsolete. -Replaced linear regulators with MP1584EN DC-DC buck converters. No RFM--noise -isn't a big concern. Buck's pin breakout not great--wouldn't fit on commercial -dev boards. +Replaced linear regulators with MP1584EN DC-DC buck converters. No RFM—noise +isn't a big concern anymore. Buck's pin breakout is not great—doesn't fit on +commercial dev boards. -Squeezed more power savings by underclocking MCU to 8MHz/3.3V. Combined -with buck converters: 56% total power savings. +Squeezed more power savings by underclocking the MCU to 8MHz/3.3V. Combined +with buck converters, 56% total power savings. Wake sequence: MCU activates FPM MOSFET, unlocks FPM over UART, scans and matches fingerprint. Match triggers blue LED, servo MOSFET, PWM signal to -- cgit v1.2.3