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docs: add Phase 1 BLE Appliance hardware requirements and Development Phases (T-E7-04)

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@ -25,6 +25,27 @@ The output feeds [pray-calc-ml](https://github.com/acamarata/pray-calc-ml), whic
Total: ~$320-465 per station. Full bill of materials and assembly guide in [docs/hardware](https://github.com/acamarata/fajr-watch/wiki/Hardware).
## Hardware Requirements (Phase 1 — BLE Appliance)
Phase 1 is a compact indoor alarm appliance that uses a TSL2591 ambient light sensor to detect
true Fajr and Isha via the solar depression angle, then triggers a buzzer. It pairs with a
companion iOS/Android app over BLE for configuration.
| Component | Model | Adafruit Price | AliExpress Price |
|---|---|---|---|
| MCU | Raspberry Pi Zero 2 W | $19.05 (Adafruit #5291) | — |
| Light sensor | TSL2591 HDR Digital Light | $6.95 (Adafruit #1980) | ~$4.50 |
| RTC | DS3231 Precision RTC STEMMA QT | $13.95 (Adafruit #5188) | ~$2.00 |
| GPS (optional) | Ultimate GPS PA1616S | $29.95 (Adafruit #746) | ~$8.00 |
| Power | PowerBoost 1000C + LiPo 2000 mAh | $32.45 (two items) | ~$8 (TP4056 + 18650) |
| Buzzer | Piezo PS1240 passive | $1.50 (Adafruit #160) | ~$0.50 |
| Enclosure | Hammond 1593KBK 100×60×25 mm | ~$6.95 (Digi-Key) | ~$3.00 |
Adafruit prototype total (no GPS): ~$97. AliExpress production total (ESP32 + no GPS): ~$28.
Full bill of materials with supplier alternatives, lead time notes, and ordering sequence:
[`.github/docs/hardware/BOM.md`](.github/docs/hardware/BOM.md)
## Quick Start
### 1. Flash the SD card
@ -159,6 +180,28 @@ Want to host a station? We provide the hardware (camera + Pi + enclosure + solar
See the [Host Guide](https://github.com/acamarata/fajr-watch/wiki/Host-Guide) for requirements and how to sign up.
## Development Phases
fajr-watch is in active development. The work breaks into three phases.
**Phase 1 — Hardware Prototype (current):** Bench prototype using a Raspberry Pi Zero 2W,
TSL2591 ambient light sensor (I2C, 0.1-88,000 lux range), and DS3231 real-time clock.
Power from USB-C mains with an 18650 LiPo backup. The device advertises a BLE GATT
service so a companion app can configure location and read sighting history. Target
hardware cost under $60. Estimated 2 weeks of build and validation work.
**Phase 2 — Firmware:** Full Python 3.11+ firmware on RPi OS Lite. The main loop polls
the TSL2591 every 60 seconds, computes the solar depression angle via the nrel-spa
algorithm, and fires an alarm (GPIO PWM buzzer) when the angle crosses the configured
threshold — defaulting to -18 degrees for Fajr. Configuration (location, depression
threshold, alarm duration) is written via BLE from the companion app and persisted
across reboots. The last 20 sighting events are readable via BLE. Estimated 3 weeks.
**Phase 3 — Companion App:** React Native (Expo SDK) app for iOS and Android. Four
screens: BLE scan and pair, settings (location and threshold configuration), sighting
history, and manual test trigger. The app communicates over BLE and requires no
background permissions — the device runs standalone once configured. Estimated 4 weeks.
## Related Projects
- [pray-calc](https://github.com/acamarata/pray-calc) - Islamic prayer time calculator (npm)