From e836c4b9e78cc3892cdebf8126cb650f1b91ed37 Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Thu, 8 Jan 2026 22:28:37 +0800 Subject: Tighten prose. --- _site/log/fpm-door-lock-rf/index.html | 44 ++++++++++++++++++----------------- 1 file changed, 23 insertions(+), 21 deletions(-) (limited to '_site/log/fpm-door-lock-rf/index.html') diff --git a/_site/log/fpm-door-lock-rf/index.html b/_site/log/fpm-door-lock-rf/index.html index d6c6b66..55675ff 100644 --- a/_site/log/fpm-door-lock-rf/index.html +++ b/_site/log/fpm-door-lock-rf/index.html @@ -46,21 +46,25 @@ lines of the transceivers to UART RXD/TXD of an ATmega328P. Unreliable–constant packet loss.

-

2025-01: Switched to RFM69 modules. A complete ball-ache. Followed the -datasheet to the letter, audited code more than 10 times, cross-checked with -RadioHead and RFM69 OSS drivers. No luck. ATmega328P runs at 5V, RFM69 3.3V. I -suspect the problem is with the logic-level converter (LLC). Not enough swing.

+

2025-01: Switched to RFM69 modules. Complete ball-ache. Followed datasheet to +the letter, audited code many times, cross-checked with RadioHead and RFM69 +open-source drivers. No luck.

-

2025-04: Ditched RFM69s. Switched to NRF24L01+ modules–5V tolerant, no LLC -required. Spent six weekends writing driver from scratch–clean-room, using -datasheet. Works perfectly.

+

Datasheet riddled with ambiguity.

-

2025-05: Wrote FPM sensor drivers for R503 and FPM10A. UART RX sequence was -tricky–took multiple attempts to get handshake working. R503 has built-in LEDs -and better form factor–will use it for the lock.

+

ATmega328P runs at 5V; RFM69 3.3V. Suspect logic-level converter (LLC) +issues. High resistance. Not enough swing.

-

2025-06: First PCB design. Two boards: fingerprint sensor (front), servo -controller (back). Encrypted RF link between them.

+

2025-04: Ditched RFM69s. Switched to NRF24L01+ modules– data pins 5V tolerant, +no LLC required. Spent six weekends writing driver from scratch–clean-room. +Works like a charm.

+ +

2025-05: Wrote FPM drivers for R503 and FPM10A. UART RX sequence was +tricky–adopted Adafruit C++ FOSS implementation to C. R503 has built-in LEDs +and better form factor. Chose it for the lock.

+ +

2025-06: Two PCB boards for FPM (front) and servo (back) controllers. Encrypted +RF link between them.

@@ -85,20 +89,18 @@ controller (back). Encrypted RF link between them.

-

PCB specs: 2-layer, 1oz copper, 0.3mm traces (0.5mm for power). Ground plane. -Both subsystems worked—could control servo from sensor over RF.

+

PCB specs: 2-layer, 1oz copper, 0.3mm traces (0.5mm for power). Ground plane.

-

2025-06: NRF24L01+ on the back controller stopped working after mounting on -PCB. RFM is too close to PWM line. Fixed by soldering a large 47uF (16V) -electrolytic capacitor between VCC and ground.

+

2025-06: NRF24L01+ on the back stopped working after mounting on PCB. Too close +to servo’s PWM line. Soldering a large 47uF (16V) electrolytic capacitor +between VCC and ground fixed it.

Power problems became clear. Linear regulators dissipated too much heat. Sensor -and servo drew 13.8mA and 4.6mA quiescent—unacceptable for battery. Servo -inrush current can exceed 1A. Trace width (0.3mm), especially for servo and -power, cutting it close.

+and servo drew 13.8mA and 4.6mA quiescent currents–unacceptable for battery. +Servo inrush current exceeds 1A. 0.3mm tracks cuts it too close.

Verdict: Functional but not practical. Battery dead in under 24 hours. Led to -complete redesign with proper power management.

+redesign with proper power management.

Commit: f4b0b73 -- cgit v1.2.3