Add support for Baldr/Rainpoint rain gauge (closes #2394)

README.md

@@ -324,6 +324,7 @@ See [CONTRIBUTING.md](./docs/CONTRIBUTING.md).
     [239]  Revolt NC-5642 Energy Meter
     [240]  LaCrosse TX31U-IT, The Weather Channel WS-1910TWC-IT
     [241]  EezTire E618 (TPMS10ATC)
+    [242]  Baldr / RainPoint rain gauge.
 
 * Disabled by default, use -R n or a conf file to enable
 

conf/rtl_433.example.conf

@@ -463,6 +463,7 @@ stop_after_successful_events false
   protocol 239 # Revolt NC-5642 Energy Meter
   protocol 240 # LaCrosse TX31U-IT, The Weather Channel WS-1910TWC-IT
   protocol 241 # EezTire E618 (TPMS10ATC)
+  protocol 242 # Baldr / RainPoint rain gauge.
 
 ## Flex devices (command line option "-X")
 

include/rtl_433_devices.h

@@ -249,6 +249,7 @@
     DECL(revolt_nc5462) \
     DECL(lacrosse_tx31u) \
     DECL(tpms_eezrv) \
+    DECL(baldr_rain) \
 
     /* Add new decoders here. */
 

src/CMakeLists.txt

@@ -61,6 +61,7 @@ add_library(r_433 STATIC
     devices/auriol_ahfl.c
     devices/auriol_hg02832.c
     devices/badger_water.c
+    devices/baldr_rain.c
     devices/blueline.c
     devices/blyss.c
     devices/brennenstuhl_rcs_2044.c

src/devices/baldr_rain.c

@@ -0,0 +1,106 @@
+/** @file
+    Baldr / RainPoint Rain Gauge protocol.
+
+    Copyright (C) 2023 Christian W. Zuckschwerdt <zany@triq.net>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+*/
+
+#include "decoder.h"
+
+/** @fn int baldr_rain_decode(r_device *decoder, bitbuffer_t *bitbuffer)
+Baldr / RainPoint Rain Gauge protocol.
+
+For Baldr Wireless Weather Station with Rain Gauge.
+See #2394
+
+Only reports rain. There's a separate temperature sensor captured by Nexus-TH.
+
+The sensor sends 36 bits 13 times,
+the packets are ppm modulated (distance coding) with a pulse of ~500 us
+followed by a short gap of ~1000 us for a 0 bit or a long ~2000 us gap for a
+1 bit, the sync gap is ~4000 us.
+
+Sample data:
+
+    {36}75b000000 [0 mm]
+    {36}75b000027 [0.9 mm]
+    {36}75b000050 [2.0 mm]
+    {36}75b8000cf [5.2 mm]
+    {36}75b80017a [9.6 mm]
+    {36}75b800224 [13.9 mm]
+    {36}75b8002a3 [17.1 mm]
+
+The data is grouped in 9 nibbles:
+
+    II IF RR RR R
+
+- I : 8 or 12-bit ID, could contain a model type nibble
+- F : 4 bit, some flags
+- R : 20 bit rain in inch/1000
+
+*/
+
+// NOTE: this should really not be here
+int rubicson_crc_check(uint8_t *b);
+
+static int baldr_rain_decode(r_device *decoder, bitbuffer_t *bitbuffer)
+{
+    int r = bitbuffer_find_repeated_row(bitbuffer, 3, 36);
+    if (r < 0)
+        return DECODE_ABORT_EARLY;
+
+    uint8_t *b = bitbuffer->bb[r];
+
+    // we expect 36 bits but there might be a trailing 0 bit
+    if (bitbuffer->bits_per_row[r] > 37)
+        return DECODE_ABORT_LENGTH;
+
+    // The baldr_rain protocol will trigger on rubicson data, so calculate the rubicson crc and make sure
+    // it doesn't match. By guesstimate it should generate a correct crc 1/255% of the times.
+    // So less then 0.5% which should be acceptable.
+    if ((b[0] == 0 && b[2] == 0 && b[3] == 0)
+            || (b[0] == 0xff &&  b[2] == 0xff && b[3] == 0xff)
+            || rubicson_crc_check(b))
+        return DECODE_ABORT_EARLY;
+
+    int id      = (b[0] << 4) | (b[1] >> 4);
+    int flags   = (b[1] & 0x0f);
+    int rain_in = (b[2] << 12) | (b[3] << 4) | (b[4] >> 4);
+
+    /* clang-format off */
+    data_t *data = data_make(
+            "model",        "",         DATA_STRING, "Baldr-Rain",
+            "id",           "",         DATA_FORMAT, "%03x", DATA_INT, id,
+            "flags",        "Flags",    DATA_FORMAT, "%x", DATA_INT, flags,
+            "rain_in",      "Rain",     DATA_FORMAT, "%.3f in", DATA_DOUBLE, rain_in,
+            NULL);
+    /* clang-format on */
+
+    decoder_output_data(decoder, data);
+    return 1;
+}
+
+static char const *output_fields[] = {
+        "model",
+        "id",
+        "flags",
+        "rain_in",
+        NULL,
+};
+
+r_device const baldr_rain = {
+        .name        = "Baldr / RainPoint rain gauge.",
+        .modulation  = OOK_PULSE_PPM,
+        .short_width = 1000,
+        .long_width  = 2000,
+        .gap_limit   = 3000,
+        .reset_limit = 5000,
+        .decode_fn   = &baldr_rain_decode,
+        .fields      = output_fields,
+        .disabled    = 0, // no checksum, disable if we encounter false-positives
+};