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Add support for La Crosse View LTV-TH2i Thermo/Hygro Sensor #3406

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Add support for La Crosse View LTV-TH2i Thermo/Hygro Sensor #3406

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8549cae
Add support for La Crosse View LTV-TH2i Thermo/Hygro Sensor
corhere Nov 14, 2025
c6b9979
Change LaCrosse LTV-TH decoder to output battery_ok, retransmit
corhere Nov 14, 2025
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42 changes: 31 additions & 11 deletions src/devices/lacrosse_th3.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
(at your option) any later version.
*/
/**
LaCrosse Technology View LTV-TH3 & LTV-TH2 Thermo/Hygro Sensor.
LaCrosse Technology View LTV-TH3, LTV-TH2 and LTV-TH2i Thermo/Hygro Sensor.

LaCrosse Color Forecast Station (model S84060) utilizes the remote
Thermo/Hygro LTV-TH3 and LTV-WR1 multi sensor (wind spd/dir and rain).
Expand All @@ -21,6 +21,7 @@ Product pages:
https://www.lacrossetechnology.com/products/ltv-th3
https://www.lacrossetechnology.com/products/C84343
https://www.lacrossetechnology.com/products/ltv-th2
https://www.lacrossetechnology.com/products/ltv-th2i

Specifications:
- Outdoor Temperature Range: -40 C to 60 C
Expand All @@ -43,7 +44,7 @@ CMT2119A and CMT2219A.
Protocol Specification:

Data bits are NRZ encoded. Logical 1 and 0 bits are 104us in
length for the LTV-TH3 and 107us for the LTV-TH2.
length for the LTV-TH3 and 107us for the LTV-TH2/2i.

LTV-TH3
SYNC:32h ID:24h ?:4b SEQ:3b ?:1b TEMP:12d HUM:12d CHK:8h END:
Expand All @@ -58,6 +59,18 @@ Sequence# 2 & 6
Sequence# 0,1,3,4,5 & 7
CHK is CRC-8 poly 0x31 init 0xac over 7 bytes following SYN

LTV-TH2i
SYNC:32h ID:24h BATTLOW:1b RETRANS:1b ?:2b SEQ:3b ?:1b TEMP:12d HUM:12d CHK:8h TRAILER:96h

CHK is CRC-8 poly 0x31 init (0x00 or 0xb2) over 7 bytes following SYN
The CRC init value for a given packet is seemingly arbitrary, though it
appears that the same init value is used for at most three packets in a row
before switching.

Pressing the TX button under the battery cover causes the sensor to
immediately retransmit the most recent packet with the RETRANS flag set.

TRAILER is 0xd2d2d2d2d200000000000000...

*/

Expand All @@ -70,8 +83,8 @@ static int lacrosse_th_decode(r_device *decoder, bitbuffer_t *bitbuffer)
data_t *data;
uint8_t b[11];
uint32_t id;
int flags, seq, offset, chk3, chk2, model_num;
int raw_temp, humidity;
int flags, seq, offset, chk3, chk2, chk2i, model_num;
int raw_temp, humidity, batt_low, retrans;
float temp_c;

// bit length is specified as 104us for the TH3 (~256 bits per packet)
Expand Down Expand Up @@ -101,16 +114,19 @@ static int lacrosse_th_decode(r_device *decoder, bitbuffer_t *bitbuffer)
bitbuffer_extract_bytes(bitbuffer, 0, offset, b, 8 * 8);

// failing the CRC checks indicates the packet is corrupt <OR>
// this is not a LTV-TH3 or LTV-TH2 sensor
// this is not a LTV-TH sensor
chk3 = crc8(b, 8, 0x31, 0x00);
chk2 = crc8(b, 8, 0x31, 0xac);
if (chk3 != 0 && chk2 != 0) {
chk2i = crc8(b, 8, 0x31, 0xb2);
if (chk3 != 0 && chk2 != 0 && chk2i != 0) {
decoder_log(decoder, 1, __func__, "CRC failed!");
return DECODE_FAIL_MIC;
}

id = (b[0] << 16) | (b[1] << 8) | b[2];
flags = (b[3] & 0xf1); // masks off seq bits
flags = (b[3] & 0x31); // masks off seq bits and known flag bits
batt_low = (b[3] & 0x80) >> 7;
retrans = (b[3] & 0x40) >> 6;
seq = (b[3] & 0x0e) >> 1;
raw_temp = b[4] << 4 | ((b[5] & 0xf0) >> 4);
humidity = ((b[5] & 0x0f) << 8) | b[6];
Expand All @@ -124,11 +140,13 @@ static int lacrosse_th_decode(r_device *decoder, bitbuffer_t *bitbuffer)
/* clang-format off */
data = data_make(
"model", "", DATA_STRING, model_num == 3 ? "LaCrosse-TH3" : "LaCrosse-TH2",
"id", "Sensor ID", DATA_FORMAT, "%06x", DATA_INT, id,
"seq", "Sequence", DATA_INT, seq,
"flags", "unknown", DATA_INT, flags,
"id", "Sensor ID", DATA_FORMAT, "%06x", DATA_INT, id,
"battery_ok", "Battery", DATA_INT, !batt_low,
"retransmit", "Retransmit", DATA_COND, retrans, DATA_INT, retrans,
"seq", "Sequence", DATA_INT, seq,
"flags", "unknown", DATA_COND, flags, DATA_INT, flags,
"temperature_C", "Temperature", DATA_FORMAT, "%.1f C", DATA_DOUBLE, temp_c,
"humidity", "Humidity", DATA_FORMAT, "%u %%", DATA_INT, humidity,
"humidity", "Humidity", DATA_FORMAT, "%u %%", DATA_INT, humidity,
"mic", "Integrity", DATA_STRING, "CRC",
NULL);
/* clang-format on */
Expand All @@ -140,6 +158,8 @@ static int lacrosse_th_decode(r_device *decoder, bitbuffer_t *bitbuffer)
static char const *const output_fields[] = {
"model",
"id",
"battery_ok",
"retransmit",
"seq",
"flags",
"temperature_C",
Expand Down