From 368e90b9de0dc56b23fcd27bc0b8fb718d3740df Mon Sep 17 00:00:00 2001
From: Stavros Korokithakis <hi@stavros.io>
Date: Sun, 5 Feb 2023 14:59:17 +0200
Subject: [PATCH] Updates

---
 content/SUMMARY.md                            |   1 +
 .../ardupilot/current-sensor-calibrator.md    | 149 ++++++++++++++++++
 content/ardupilot/index.md                    |   1 +
 3 files changed, 151 insertions(+)
 create mode 100644 content/ardupilot/current-sensor-calibrator.md

diff --git a/content/SUMMARY.md b/content/SUMMARY.md
index eb01489..7eae999 100644
--- a/content/SUMMARY.md
+++ b/content/SUMMARY.md
@@ -8,6 +8,7 @@
         - [Bitmask calculator](ardupilot/bitmask-calculator.md)
         - [Building ArduPilot](ardupilot/building-ardupilot.md)
         - [Configuring a switch as a relay](ardupilot/configuring-a-switch-as-a-relay.md)
+        - [Current sensor calibrator](ardupilot/current-sensor-calibrator.md)
         - [DJI FPV configuration](ardupilot/dji-fpv-configuration.md)
         - [ELRS preferred configuration](ardupilot/elrs-preferred-configuration.md)
         - [Installing WTFOS on DJI](ardupilot/installing-wtfos-on-dji.md)
diff --git a/content/ardupilot/current-sensor-calibrator.md b/content/ardupilot/current-sensor-calibrator.md
new file mode 100644
index 0000000..80f3dba
--- /dev/null
+++ b/content/ardupilot/current-sensor-calibrator.md
@@ -0,0 +1,149 @@
+# Current sensor calibrator
+
+<style>
+    div.box{
+        /* width: 90%; */
+    }
+    .number {
+        width: 60px;
+    }
+</style>
+
+<script type="text/javascript">
+// 1674123219
+
+function precisionRoundMod(number, precision) {
+    var factor = Math.pow(10, precision);
+    var n = precision < 0 ? number : 0.01 / factor + number;
+    return Math.round( n * factor) / factor;
+    }
+
+function apcalc() {
+    scale = 100;
+    const measurements = [];
+    const realvalues = [];
+    const coeffs = [];
+    const scale_adjusted_meas = [];
+    const current_offsets = [];
+
+    for (var i = 1; i < 5; i++)
+    {
+        meas = parseFloat(document.getElementById('m'+i).value);
+        real = parseFloat(document.getElementById('r'+i).value);
+        measurements.push(meas);
+        realvalues.push(real);
+
+        if(i != 1){
+            var p=i;
+            p--;
+            pmeas = parseFloat(document.getElementById('m'+p).value);
+            preal = parseFloat(document.getElementById('r'+p).value);
+            coeffs.push( (meas-pmeas)/ (real-preal) );
+        }
+    }
+
+    for(var i=0, n=coeffs.length; i < n; i++)
+    {
+        console.log("coeff: "+parseFloat(coeffs[i]));
+    }
+
+    console.log("coeff sum: "+coeffs.reduce((partialSum, a) => partialSum + a, 0));
+    const avg_coeffs = coeffs.reduce((partialSum, a) => partialSum + a, 0) / coeffs.length;
+    console.log("coeff avg: "+avg_coeffs);
+
+    for(var i=0, n=measurements.length; i < n; i++)
+    {
+        scale_adjusted_meas.push(measurements[i]/avg_coeffs);
+        console.log("scale_adjusted_meas: "+measurements[i]/avg_coeffs);
+    }
+
+    for(var i=0, n=realvalues.length; i < n; i++)
+    {
+        current_offsets.push(scale_adjusted_meas[i] - realvalues[i]);
+        console.log(scale_adjusted_meas[i] - realvalues[i] );
+    }
+
+    const avg_offset = current_offsets.reduce((partialSum, a) => partialSum + a, 0) / current_offsets.length;
+    console.log("avg_offset: "+avg_offset);
+
+    document.getElementById('r_offset').value = precisionRoundMod( (avg_offset / (scale / avg_coeffs)), 4 );
+    document.getElementById('r_scale').value = precisionRoundMod( (scale / avg_coeffs) ,4);
+}
+
+function init() {
+	document.querySelectorAll("input").forEach(input => {
+		input.addEventListener("input", apcalc);
+	});
+}
+
+window.onload = init;
+</script>
+
+This calculator will allow you to calibrate your current sensor better than with the mAh charged vs mAh consumed method. 
+You need a current meter and a way to see what current and throttle percentage the FC reports (the OSD is a good way to do this).
+The steps to follow are:
+0. Make sure you have capacitors on ESCs so the measurement will not be influenced by errors from ESC noise.
+1. Set `BATT_AMP_PERVLT=100` and `BATT_AMP_OFFSET=0`.
+3. Power your plane with propellers on and a current meter connected between FC and pack.
+4. Arm and run the motor in manual mode. For four different throttle positions, note down: The throttle position (from the OSD), the reported current (from the OSD), and the actual current (from the current meter). The best throttle positions to use would be 25%, 50%, 75% and 100%. Do not check current on idle as this will be inaccurate.
+5. Enter the values below, and the calculator will give you the proper BATT_AMP_PERVLT and BATT_AMP_OFFSET values that you now need to write to your plane's parameters.
+
+
+<div class="box">
+    <div id="input">
+        <table style="border: none">
+            <tr>
+                <td>Throttle:</td>
+                <td>
+                    <input class="number" type="text" id="m1" value="25" placeholder="OSD value">
+                    <input class="number" type="text" id="m2" value="50" placeholder="OSD value">
+                    <input class="number" type="text" id="m3" value="75" placeholder="OSD value">
+                    <input class="number" type="text" id="m4" value="100" placeholder="OSD value">
+                </td>
+            </tr>
+            <tr>
+                <td>
+                    Current:
+                </td>
+                <td>
+                    <input class="number" type="text" id="r1" value="2.0" placeholder="current meter">
+                    <input class="number" type="text" id="r2" value="4.0" placeholder="current meter" >
+                    <input class="number" type="text" id="r3" value="8.0" placeholder="current meter" >
+                    <input class="number" type="text" id="r4" value="12.0" placeholder="current meter">
+                </td>
+            </tr>
+            <tr>
+                <td>
+                    <br>Results:<br>
+                </td>
+            </tr>
+            <tr>
+                <td>
+                    <code>BATT_AMP_OFFSET</code>:
+                </td>
+                <td>
+                    <input class="number" type="text" id="r_offset" value="" placeholder="offset" ><br>
+                </td>
+            </tr>
+            <tr>
+                <td>
+                    <code>BATT_AMP_PERVLT</code>:
+                <td>
+                    <input class="number" type="text" id="r_scale" value="" placeholder="scale" >
+                </td>
+            </tr>
+        </table>
+    </div>
+    <br>
+    <div id="result">
+    </div>
+</div>
+
+_(Many thanks to mfoos for writing this note.)_
+
+* * *
+
+<p style="font-size:80%; font-style: italic">
+Last updated on February 05, 2023. For any questions/feedback,
+email me at <a href="mailto:hi@stavros.io">hi@stavros.io</a>.
+</p>
diff --git a/content/ardupilot/index.md b/content/ardupilot/index.md
index c696611..36cf1fd 100644
--- a/content/ardupilot/index.md
+++ b/content/ardupilot/index.md
@@ -7,6 +7,7 @@ Click on a link in the list below to go to that page:
 1. [Bitmask calculator](../../ardupilot/bitmask-calculator.html)
 1. [Building ArduPilot](../../ardupilot/building-ardupilot.html)
 1. [Configuring a switch as a relay](../../ardupilot/configuring-a-switch-as-a-relay.html)
+1. [Current sensor calibrator](../../ardupilot/current-sensor-calibrator.html)
 1. [DJI FPV configuration](../../ardupilot/dji-fpv-configuration.html)
 1. [ELRS preferred configuration](../../ardupilot/elrs-preferred-configuration.html)
 1. [Installing WTFOS on DJI](../../ardupilot/installing-wtfos-on-dji.html)