/* Schrader variant EG53MA4 TPMS. * Usually 443.92 Mhz OOK, 100us pulse len. * * Preamble: alternating pulse/gap, 100us. * Sync (as pulses and gaps): "01100101", already part of the data stream * (first nibble) corresponding to 0x4 * * A total of 10 bytes payload, Manchester encoded. * * 0 = 01 * 1 = 10 * * Used in certain Open cars and others. */ #include "../../app.h" static bool decode(uint8_t* bits, uint32_t numbytes, uint32_t numbits, ProtoViewMsgInfo* info) { const char* sync_pattern = "010101010101" "01100101"; uint8_t sync_len = 12 + 8; /* We just use 12 preamble symbols + sync. */ if(numbits - sync_len + 8 < 8 * 10) return false; uint64_t off = bitmap_seek_bits(bits, numbytes, 0, numbits, sync_pattern); if(off == BITMAP_SEEK_NOT_FOUND) return false; FURI_LOG_E(TAG, "Schrader EG53MA4 TPMS preamble+sync found"); info->start_off = off; off += sync_len - 8; /* Skip preamble, not sync that is part of the data. */ uint8_t raw[10]; uint32_t decoded = convert_from_line_code( raw, sizeof(raw), bits, numbytes, off, "01", "10"); /* Manchester code. */ FURI_LOG_E(TAG, "Schrader EG53MA4 TPMS decoded bits: %lu", decoded); if(decoded < 10 * 8) return false; /* Require the full 10 bytes. */ /* CRC is just all bytes added mod 256. */ uint8_t crc = 0; for(int j = 0; j < 9; j++) crc += raw[j]; if(crc != raw[9]) return false; /* Require sane CRC. */ info->pulses_count = (off + 10 * 8 * 2) - info->start_off; /* To convert the raw pressure to kPa, RTL433 uses 2.5, but is likely * wrong. Searching on Google for users experimenting with the value * reported, the value appears to be 2.75. */ float kpa = (float)raw[7] * 2.75; int temp_f = raw[8]; int temp_c = (temp_f - 32) * 5 / 9; /* Convert Fahrenheit to Celsius. */ snprintf(info->name, sizeof(info->name), "%s", "Schrader EG53MA4 TPMS"); snprintf( info->raw, sizeof(info->raw), "%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X", raw[0], raw[1], raw[2], raw[3], raw[4], raw[5], raw[6], raw[7], raw[8], raw[9]); snprintf( info->info1, sizeof(info->info1), "Tire ID %02X%02X%02X", raw[4], raw[5], raw[6]); /* Only 28 bits of ID, not 32. */ snprintf(info->info2, sizeof(info->info2), "Pressure %.2f kpa", (double)kpa); snprintf(info->info3, sizeof(info->info3), "Temperature %d C", temp_c); return true; } ProtoViewDecoder SchraderEG53MA4TPMSDecoder = {"Schrader EG53MA4 TPMS", decode};