correcting adc temp calculation.

lua_modules/adc-ntc/README.md

@@ -7,15 +7,37 @@ Schematic is:
 
 The default configuration is defined for:
 
-- VCC=5V
+- VccR1=5V
 - R1=330k
 - Rntc=50k
+- NodeMCU board
 
-$Vntc = VCC * Rntc / ( Rntc + R1 )$
+_Note: stock ESP8266 chip accepts 1V in A0 input. NodeMCU boards are shipped with built-in voltage divider and accept 3.3V._
 
-$Adc = 1023 * Vntc / 3.3$
+Since resistor and voltage values are not perfect, there are some discrepancies between schematic and reality.
+There are two way to influence for biased results:
 
-where 1023 is Adc resolution and 3.3V is the A0 input max voltage i.e. NodeMCU board. Plain ESP8266 chips accept 1v max.
+- Adjust R1 resistor value in the settings.
+  - With default configuration, each +15k => +1C.
+- Use `correction factor`.
+  - Correction factor is ADC value added to A0 reading before Vntc is being calculated.
+  - With default configuration, +9 => +1C.
+
+Perform temperature calibration or observe long term and adjust these if you see fit.
+
+$Vstep = VccA0 / 1023$
+
+$AdcValue = A0 + correction_factor$
+
+$Vntc = Vstep * AdvValue$
+
+$Rntc = R1 * Vntc / ( VccR1 - Vntc )$
+
+$TempK = A + B * ln(Rntc) + C * ln(Rntc)^3$
+
+$TempC = TempK - 273.15$
+
+With default configuration following values could be expected:
 
 | Temp (C) | Rntc (kOhm) | Vntc (V) | Adc (0-1024) |
 | -------- | ----------- | -------- | ------------ |

lua_modules/adc-ntc/fs/fs-adc-ntc.json

@@ -1,6 +1,7 @@
 {
-  "AdcCorr": 1.09,
-  "Vcc": 3.3,
+  "AdcCorr": 0,
+  "VccA0": 3.3,
+  "VccR1": 5,
   "R1": 330000,
   "A": 9.656249129e-4,
   "B": 2.106952165e-4,

lua_modules/adc-ntc/lua/adc-ntc.lua

@@ -9,7 +9,8 @@ local adc = require("adc")
 
 ---@class adcNtc_cfg
 ---@field AdcCorr integer correction factor for read ADC values. 1 means no correction.
----@field Vcc integer max voltage at A0 input i.e 3.3V for NodeMCU and 1V for ESP8266
+---@field VccA0 integer max voltage at A0 input i.e 3.3V for NodeMCU and 1V for ESP8266
+---@field VccR1 integer voltage at R1 i.e 5V or 3.3V
 ---@field R1 integer resistor 1 in Kohm
 ---@field A number Steinhart-Hart model coefficient
 ---@field B number Steinhart-Hart model coefficient
@@ -36,9 +37,10 @@ end
 local function main(onReadCb)
     package.loaded[modname] = nil
 
-    local AdcValue = readAvg(20) * cfg.AdcCorr
-    local Vntc = cfg.Vcc * AdcValue / 1023
-    local Rntc = cfg.R1 * Vntc / (cfg.Vcc - Vntc)
+    local Vstep = cfg.VccA0 / 1023
+    local AdcValue = readAvg(20) + cfg.AdcCorr
+    local Vntc = Vstep * AdcValue
+    local Rntc = cfg.R1 * Vntc / (cfg.VccR1 - Vntc)
     local LogRntc = math.log(Rntc)
     local bVal = cfg.B * LogRntc
     local cVal = cfg.C * LogRntc * LogRntc * LogRntc

lua_modules/web-portal/fs/wifi-portal.html

@@ -380,16 +380,18 @@ <h3 class="collapsible">Temp Sensor (ds18b20)</h3>
         <h3 class="collapsible">Temp Sensor (adc NTC)</h3>
         <div class="collapsible-content grid-container">
           <label for="adcNtc_AdcCorr" class="grid-item"
-            >Read ADC-values correction factor<br />
-            use this to long term tune temp calculation<br />
-            start with 1 (no correction) and adjust<br />
+            >Read ADC-values correction factor.<br />
+            Use this to long term tune temp calculation.<br />
+            Start with 0 (no correction) increase/decrease<br />
             after comparing room temp and sensor results:</label
           >
-          <input id="adcNtc_AdcCorr" class="cfgValue grid-item" type="number" />
+          <input id="adcNtc_AdcCorr" class="cfgValue grid-item" type="number" step="1" />
           <label for="adcNtc_R1" class="grid-item">Resistor 1 (ohm):</label>
           <input id="adcNtc_R1" class="cfgValue grid-item" type="number" min="1" />
-          <label for="adcNtc_Vcc" class="grid-item">VCC (V):</label>
-          <input id="adcNtc_Vcc" class="cfgValue grid-item" type="number" min="1" />
+          <label for="adcNtc_VccA0" class="grid-item">VCC at A0 (V)<br />i.e 3.3 (NodeMCU) or 1 (ESP):</label>
+          <input id="adcNtc_VccA0" class="cfgValue grid-item" type="number" min="1" />
+          <label for="adcNtc_VccR1" class="grid-item">VCC at R1 (V)<br />likely 3.3 or 5:</label>
+          <input id="adcNtc_VccR1" class="cfgValue grid-item" type="number" min="1" />
           <label for="adcNtc_A" class="grid-item">Steinhart-Hart model coefficient A:</label>
           <input id="adcNtc_A" class="cfgValue grid-item" type="number" min="1" />
           <label for="adcNtc_B" class="grid-item">Steinhart-Hart model coefficient B:</label>