Add support for HG9901 moisture sensor

README.md

@@ -360,6 +360,7 @@ See [CONTRIBUTING.md](./docs/CONTRIBUTING.md).
     [272]  Landis & Gyr Gridstream Power Meters 19.2k
     [273]  Landis & Gyr Gridstream Power Meters 38.4k
     [274]  Revolt ZX-7717 power meter
+    [275]* HG9901 Moisture sensor
 
 * Disabled by default, use -R n or a conf file to enable
 

conf/rtl_433.example.conf

@@ -504,6 +504,7 @@ convert si
   protocol 272 # Landis & Gyr Gridstream Power Meters 19.2k
   protocol 273 # Landis & Gyr Gridstream Power Meters 38.4k
   protocol 274 # Revolt ZX-7717 power meter
+# protocol 275 # HG9901 Moisture sensor
 
 ## Flex devices (command line option "-X")
 

include/rtl_433_devices.h

@@ -282,6 +282,7 @@
     DECL(gridstream192) \
     DECL(gridstream384) \
     DECL(revolt_zx7717) \
+    DECL(hg9901) \
 
     /* Add new decoders here. */
 

src/CMakeLists.txt

@@ -139,6 +139,7 @@ add_library(r_433 STATIC
     devices/gt_wt_02.c
     devices/gt_wt_03.c
     devices/hcs200.c
+    devices/hg9901.c
     devices/hideki.c
     devices/holman_ws5029.c
     devices/hondaremote.c

src/devices/hg9901.c

@@ -0,0 +1,130 @@
+/** @file
+    Moisture Sensor HG9901 - Homelead, Reyke, Dr.meter, Vodeson, Midlocater, Kithouse, Vingnut.
+
+    Copyright (C) 2025 Inonoob
+
+    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"
+
+/**
+Moisture Sensor HG9901 - Moisture Sensor HG9901 - Homelead, Reyke, Dr.meter, Vodeson, Midlocater, Kithouse, Vingnut.
+
+This device is a simple garden temperature/moisture transmitter with a small LCD display for local viewing.
+
+A message seems to have 65 bits.
+
+Data layout:
+
+    Byte 0   Byte 1   Byte 2   Byte 3   Byte 4   Byte 5   Byte 6   Byte 7   Byte 8
+     55	      aa       30       06       e4        ff      0f        3f       8
+
+Format string:
+
+  SENSOR_ID:hhhh Soil moisture:hh Temperature:hh Battery:h Light intensity:hh unknown:b
+
+Example packets:
+
+  55aa 3006 e4 ff 0f 3f 8
+  55aa 7f29 de fc 0f 1f 8
+
+inverted:
+
+ aa55 cff9 1b 00 f 0c 07
+ aa55 80d6 21 03 f 0e 07
+
+The sensor will send a message every 31 min if no changes are measured.
+If changes are measured the sensor will instantly send messages.
+
+Light intensity mapping (just a guess so far):
+- LOW-: 0 - 10
+- LOW: 11 - 30
+- LOW+: 31 - 33
+- NOR-: 34 - 50
+- NOR: 51 - 66
+- NOR+: 67 - 70
+- HIGH-: 71 - 77
+- HIGH: 78 - 85
+- HIGH+: 86 - 133
+
+*/
+static int hg9901_decode(r_device *decoder, bitbuffer_t *bitbuffer)
+{
+    // Loop through all rows in the bitbuffer to process all potential packets
+    for (int i = 0; i < bitbuffer->num_rows; ++i) {
+        uint8_t *b = bitbuffer->bb[i];
+
+        // Ensure that the length of the packet is correct (65 bits)
+        if (bitbuffer->bits_per_row[i] != 65) {
+            continue;  // Skip this row if the length is not correct
+        }
+
+        // Check if the first two bytes are the correct preamble (0x55 0xAA)
+        if (b[0] != 0x55 || b[1] != 0xaa) {
+            continue;  // Skip this row if the preamble is invalid
+        }
+
+        decoder_log_bitbuffer(decoder, 2, __func__, bitbuffer, "After preamble check");
+
+        // Invert the bits of the entire packet (only if valid)
+        bitbuffer_invert(bitbuffer);
+
+        decoder_log_bitbuffer(decoder, 2, __func__, bitbuffer, "After invert");
+
+        // Extract the data from the packet (after inversion)
+        int sensor_id       = (b[2] << 8) | (b[3]);               // Sensor ID from bytes 2 and 3
+        int soil_moisture   = b[4];                               // Humidity from byte 4
+        int temp_raw        = b[5];                               // Temperature from byte 5
+        int battery_raw     = (b[6] & 0xf0) >> 4;                 // Battery status is together with the light value
+        int light_intensity = ((b[6] & 0x0f) << 4) | (b[7] >> 4); // Light Intensity needs to be put togther from byte 6 and byte 7
+        int light_lux       = light_intensity * 100;
+
+        if (temp_raw >= 0x80) { // temperature has a dedicated sign bit
+            temp_raw = 0x80 - temp_raw;
+        }
+
+        float battery_pct = battery_raw * 0.066667f; // Observed battery states are 0x3, 0x7, 0xb, 0xf (i.e. 0-15)
+
+        /* clang-format off */
+        data_t *data = data_make(
+                "model",            "",                 DATA_STRING, "HG9901",
+                "id",               "Sensor ID",        DATA_INT,    sensor_id,
+                "battery_ok",       "Battery",          DATA_DOUBLE, battery_pct,
+                "temperature_C",    "Temperature",      DATA_FORMAT, "%d C", DATA_INT, temp_raw,
+                "moisture",         "Soil moisture",    DATA_FORMAT, "%u %%", DATA_INT, soil_moisture,
+                "light_lux",        "Light",            DATA_FORMAT, "%u lux", DATA_INT, light_lux,
+                NULL);
+        /* clang-format on */
+
+        decoder_output_data(decoder, data);
+        return 1;  // Successfully decoded one valid packet and returned
+    }
+
+    return DECODE_ABORT_LENGTH;  // No valid packet found
+}
+
+static char const *const output_fields[] = {
+        "model",
+        "id",
+        "battery_ok",
+        "temperature_C",
+        "moisture",
+        "light_lux",
+        NULL,
+};
+
+r_device const hg9901 = {
+        .name        = "HG9901 moisture sensor",
+        .modulation  = OOK_PULSE_PWM,
+        .short_width = 600,  // plus gap 1000
+        .long_width  = 1400, // plus gap 200
+        .gap_limit   = 1200,
+        .reset_limit = 4000, // packet gap is 3800
+        .decode_fn   = &hg9901_decode,
+        .disabled    = 1, // Disabled by default as there is no checksum
+        .fields      = output_fields,
+};