From 03944e6cd8858f42ab0cf730d8e1dbddd559aa81 Mon Sep 17 00:00:00 2001
From: DAVe3283 <DAVe3283@gmail.com>
Date: Tue, 7 Jun 2022 15:58:32 -0600
Subject: [PATCH] Fix bogus reading on no communication with MAX31865 (#3505)

---
 CODEOWNERS                               | 1 +
 esphome/components/max31865/max31865.cpp | 8 ++++++++
 esphome/components/max31865/sensor.py    | 3 +++
 3 files changed, 12 insertions(+)

diff --git a/CODEOWNERS b/CODEOWNERS
index d5ce5e6920..3cb38fce06 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -103,6 +103,7 @@ esphome/components/lilygo_t5_47/touchscreen/* @jesserockz
 esphome/components/lock/* @esphome/core
 esphome/components/logger/* @esphome/core
 esphome/components/ltr390/* @sjtrny
+esphome/components/max31865/* @DAVe3283
 esphome/components/max44009/* @berfenger
 esphome/components/max7219digit/* @rspaargaren
 esphome/components/max9611/* @mckaymatthew
diff --git a/esphome/components/max31865/max31865.cpp b/esphome/components/max31865/max31865.cpp
index 126915dc15..152d7b340b 100644
--- a/esphome/components/max31865/max31865.cpp
+++ b/esphome/components/max31865/max31865.cpp
@@ -94,6 +94,14 @@ void MAX31865Sensor::read_data_() {
   const uint16_t rtd_resistance_register = this->read_register_16_(RTD_RESISTANCE_MSB_REG);
   this->write_config_(0b11000000, 0b00000000);
 
+  // Check for bad connection
+  if (rtd_resistance_register == 0b0000000000000000 || rtd_resistance_register == 0b1111111111111111) {
+    ESP_LOGE(TAG, "SPI bus read all 0 or all 1 (0x%04X), check MAX31865 wiring & power.", rtd_resistance_register);
+    this->publish_state(NAN);
+    this->status_set_error();
+    return;
+  }
+
   // Check faults
   const uint8_t faults = this->read_register_(FAULT_STATUS_REG);
   if ((has_fault_ = faults & 0b00111100)) {
diff --git a/esphome/components/max31865/sensor.py b/esphome/components/max31865/sensor.py
index 6eb8bd400d..704f945171 100644
--- a/esphome/components/max31865/sensor.py
+++ b/esphome/components/max31865/sensor.py
@@ -11,6 +11,9 @@ from esphome.const import (
     UNIT_CELSIUS,
 )
 
+CODEOWNERS = ["@DAVe3283"]
+DEPENDENCIES = ["spi"]
+
 max31865_ns = cg.esphome_ns.namespace("max31865")
 MAX31865Sensor = max31865_ns.class_(
     "MAX31865Sensor", sensor.Sensor, cg.PollingComponent, spi.SPIDevice