Document 433/868 MHz variants

README.md

@@ -3,7 +3,10 @@
 Unified firmware for LilyGO T3 v1.6.1 (ESP32 + SX1276 + SSD1306) that runs as **Sender** or **Receiver** based on a GPIO jumper. Senders read DD3 smart meter values, compress JSON, and transmit over LoRa. The receiver validates packets, publishes to MQTT, provides a web UI, and shows per-sender status on the OLED.
 
 ## Hardware
-Board: **LilyGO T3 LoRa32 v1.6.1** (ESP32 + SX1276 433 MHz + SSD1306 128x64 + LiPo)
+Board: **LilyGO T3 LoRa32 v1.6.1** (ESP32 + SX1276 + SSD1306 128x64 + LiPo)
+Variants:
+- SX1276 **433 MHz** module (default build)
+- SX1276 **868 MHz** module (use 868 build environments)
 
 ### Pin Mapping
 - LoRa (SX1276)
@@ -157,7 +160,8 @@ Packet layout:
 ```
 
 LoRa radio settings:
-- 433 MHz, SF12, BW 125 kHz, CR 4/5, CRC on, Sync Word 0x34
+- Frequency: **433 MHz** or **868 MHz** (set by build env via `LORA_FREQUENCY_HZ`)
+- SF12, BW 125 kHz, CR 4/5, CRC on, Sync Word 0x34
 
 ## Data Format
 JSON payload (sender + MQTT):
@@ -269,3 +273,15 @@ Test mode:
 pio run -e lilygo-t3-v1-6-1-test -t upload --upload-port COMx
 ```
 
+868 MHz builds:
+
+```bash
+pio run -e lilygo-t3-v1-6-1-868 -t upload --upload-port COMx
+```
+
+868 MHz test mode:
+
+```bash
+pio run -e lilygo-t3-v1-6-1-868-test -t upload --upload-port COMx
+```
+