49 lines
2.1 KiB
Markdown
49 lines
2.1 KiB
Markdown
# QuadMeUp Crossbow
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_QuadMeUp Crossbow_ is a DIY project that gives 5km (at least) of RC link for UAV (airplanes and drones) for a price below $40. I uses SX1276 (LoRa 868MHz/915MHz) compatible (like HopeRF RFM95W) radio modules connected to Arduino compatible boards. It can be regular Arduino connected via SPI to SX1276 or dedicated board like _Adafruit Feather 32u4 RFM LoRa_ or _LoRa32u4 II_
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# Current state
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Development, not yet functional
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# Protocol
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| Byte | Description | Notes |
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| ---- | ---- | ---- |
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| 1 | Preamble | "Q" 0x51 |
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| 2 | Channel ID | channel used for comunication between TX and RX |
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| 3 | Frame type & Length | bits 7-5 defines frame, bits 4-0 payload length |
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| 4 | Packet ID | |
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| 5 - 36 | Payload | 32 bytes max |
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| payload length + 5 | CRC | XOR of all previous bytes |
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## Frame types
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| Value | Value hex | Description | Direction |
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| ---- | ---- |---- | ---- |
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| 0000 | 0x0 | RC channels data `RC_DATA` | TX -> RX |
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| 0001 | 0x1 | Receiver health and basic telemetry `RX_HEALTH` | RX -> TX |
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| 0010 | 0x2 | Request receiver configuration | TX -> RX |
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| 0011 | 0x3 | Receiver configuration | RX -> TX |
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| 0100 | 0x4 | Set receiver configuration | TX -> RX |
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### `RC_DATA` frame format
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Protocol allows to send 10 RC channels in total encoded as following
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* channels 1 to 4 encoded using 10 bits each (5 bytes)
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* channels 5 to 6 encoded using 8 bits each (2 bytes)
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* channels 7 to 10 encoded using 4 bits per channel (2 bytes)
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Total length of `RC_DATA` payload is 9 bytes
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### `RX_HEALTH` frame format
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| Byte | Description |
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| ---- | ---- |
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| 0 | RX RSSI |
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| 1 | RX SNR |
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| 2 | RX supply volatage, sent in 0,1V |
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| 3 | RX analog input 1 sent in 0,1V |
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| 4 | RX analog input 2 sent in 0,1V |
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