From 5bce26d9b76e204058efe41ef33f24de04364722 Mon Sep 17 00:00:00 2001
From: Alexander Balya <alexander.balya@gmail.com>
Date: Mon, 25 May 2026 04:03:24 +0200
Subject: [PATCH] Fix SHT2x detection for INA219 addresses (#10482)

---
 src/detect/ScanI2CTwoWire.cpp | 37 +++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/detect/ScanI2CTwoWire.cpp b/src/detect/ScanI2CTwoWire.cpp
index e3471c32a..c1c48eac8 100644
--- a/src/detect/ScanI2CTwoWire.cpp
+++ b/src/detect/ScanI2CTwoWire.cpp
@@ -179,8 +179,22 @@ String readSEN5xProductName(TwoWire *i2cBus, uint8_t address)
 #endif
 
 #if HAS_TELEMETRY && !MESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR
+static uint8_t crcSHT2X(const uint8_t *data, uint8_t len)
+{
+    uint8_t crc = 0;
+    for (uint8_t i = 0; i < len; i++) {
+        crc ^= data[i];
+        for (uint8_t bit = 0; bit < 8; bit++) {
+            crc = (crc & 0x80) ? (crc << 1) ^ 0x31 : crc << 1;
+        }
+    }
+    return crc;
+}
+
 bool detectSHT21SerialNumber(TwoWire *i2cBus, uint8_t address)
 {
+    uint8_t serialA[8] = {0};
+    uint8_t serialB[6] = {0};
 
     i2cBus->beginTransmission(address);
     i2cBus->write(0xFA);
@@ -189,12 +203,13 @@ bool detectSHT21SerialNumber(TwoWire *i2cBus, uint8_t address)
     if (i2cBus->endTransmission() != 0)
         return false;
 
-    if (i2cBus->requestFrom(address, (uint8_t)8) != 8)
+    if (i2cBus->requestFrom(address, (uint8_t)sizeof(serialA)) != sizeof(serialA))
         return false;
 
-    // Just flush the data
-    while (i2cBus->available() < 8) {
-        i2cBus->read();
+    for (uint8_t i = 0; i < sizeof(serialA); i++) {
+        if (!i2cBus->available())
+            return false;
+        serialA[i] = i2cBus->read();
     }
 
     i2cBus->beginTransmission(address);
@@ -204,16 +219,18 @@ bool detectSHT21SerialNumber(TwoWire *i2cBus, uint8_t address)
     if (i2cBus->endTransmission() != 0)
         return false;
 
-    if (i2cBus->requestFrom(address, (uint8_t)6) != 6)
+    if (i2cBus->requestFrom(address, (uint8_t)sizeof(serialB)) != sizeof(serialB))
         return false;
 
-    // Just flush the data
-    while (i2cBus->available() < 6) {
-        i2cBus->read();
+    for (uint8_t i = 0; i < sizeof(serialB); i++) {
+        if (!i2cBus->available())
+            return false;
+        serialB[i] = i2cBus->read();
     }
 
-    // Assume we detect the SHT21 if something came back from the request
-    return true;
+    return crcSHT2X(&serialA[0], 1) == serialA[1] && crcSHT2X(&serialA[2], 1) == serialA[3] &&
+           crcSHT2X(&serialA[4], 1) == serialA[5] && crcSHT2X(&serialA[6], 1) == serialA[7] &&
+           crcSHT2X(&serialB[0], 2) == serialB[2] && crcSHT2X(&serialB[3], 2) == serialB[5];
 }
 #endif