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Diffstat (limited to '_log')
| -rw-r--r-- | _log/fpm-door-lock-lp.md | 34 |
1 files changed, 17 insertions, 17 deletions
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. <video style="max-width:100%;" controls="" poster="pcb.jpg"> <source src="video.mp4" type="video/mp4"> </video> -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. <table style="border: none; width: 100%"> <tr style="border: none;"> @@ -36,18 +36,18 @@ attaches to interior knob, MCU stays on the back to prevent tampering. </table> 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 |