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Diffstat (limited to '_log/fpm-door-lock-rf.md')
| -rw-r--r-- | _log/fpm-door-lock-rf.md | 42 |
1 files changed, 22 insertions, 20 deletions
diff --git a/_log/fpm-door-lock-rf.md b/_log/fpm-door-lock-rf.md index 76f64d7..87dc6b4 100644 --- a/_log/fpm-door-lock-rf.md +++ b/_log/fpm-door-lock-rf.md @@ -12,21 +12,25 @@ Wanted to unlock door with fingerprint, wirelessly to avoid drilling. 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. <table style="border: none; width: 100%"> <tr style="border: none;"> @@ -52,19 +56,17 @@ controller (back). Encrypted RF link between them. </table> 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. -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](../fpm-door-lock-lp/) with proper power management. +[redesign](../fpm-door-lock-lp/) with proper power management. Commit: [f4b0b73](https://git.asciimx.com/smart-home/commit/?id=f4b0b734a595919cf451ab9448b06274c8e609a4) |