arduino-battery-sensing.html

<html>
<head>
<title>Arduino Battery Sensing Circuit Calculator</title>
</head>
<body>
<form>
	<div style="float:left;">
		<div>
			<div style="border: solid 1px; margin: 1rem; padding: 0.5rem; width: 15rem;">
				<div style="text-align:right;">
					<span style="float: left;">Battery Max Voltage:</span>
					<input id="bat-max" style="width:3rem;" placeholder="12.6" /> v
				</div>
				<div style="text-align:right;">
					<span style="float: left;">Battery Min Voltage:</span>
					<input id="bat-min" style="width:3rem;" placeholder="9" onchange="populateZener()"/> v
				</div>
			</div>
			<div style="border: solid 1px; margin: 1rem; padding: 0.5rem; width: 15rem;">
				<div style="text-align:right;">
					<span style="float: left;">ADC Max Voltage:</span>
					<input id="adc-max" style="width:3rem;" placeholder="1.1" /> v
				</div>
				<div style="text-align:right;">
					<span style="float: left;">ADC Min Voltage:</span>
					<input id="adc-min" style="width:3rem;" placeholder="0" /> v
				</div>
			</div>
			<div style="margin: 0 1rem; text-align:right; padding: 0.5rem; width: 15rem;">
				<span style="float: left;">Zener Drop Diode:</span>
				<select id="zener">
					<option value="0">-none-</option>
					<option value="2">2v</option>
					<option value="2.2">2.2v</option>
					<option value="2.4">2.4v</option>
					<option value="2.7">2.7v</option>
					<option value="3">3v</option>
					<option value="3.3">3.3v</option>
					<option value="3.6">3.6v</option>
					<option value="3.9">3.9v</option>
					<option value="4.3">4.3v</option>
					<option value="4.7">4.7v</option>
					<option value="5.1">5.1v</option>
					<option value="5.6">5.6v</option>
					<option value="6.2">6.2v</option>
					<option value="6.8">6.8v</option>
					<option value="7.5">7.5v</option>
					<option value="8.2">8.2v</option>
					<option value="9.1">9.1v</option>
					<option value="10">10v</option>
					<option value="11">11v</option>
					<option value="12">12v</option>
					<option value="13">13v</option>
					<option value="15">15v</option>
					<option value="16">16v</option>
					<option value="18">18v</option>
					<option value="20">20v</option>
					<option value="22">22v</option>
					<option value="24">24v</option>
					<option value="27">27v</option>
					<option value="30">30v</option>
					<option value="39">39v</option>
				</select>
			</div>
			<div style="margin: 0 1rem; text-align:right; padding: 0.5rem; width: 15rem;">
				<span style="float: left;">Sense Current:</span>
				<input id="current" style="width:3rem;" placeholder="1" value="5"/> mA
			</div>
			<div style="margin: 0 1rem; text-align:right; padding: 0.5rem; width: 15rem;">
				<span style="float: left;">Resistors to Use:</span>
				<select id="resistor-series">
					<option value="12">E12  (±10%)</option>
				</select>
			</div>
			<div style="position:relative">
				<button style="width:100%; height:2rem;" type="button" id="bnt_calculate" onclick="calculate()">Calculate</button>
			</div>
		</div>
	<div id="results" style="margin-top: 6rem">
		<div style="border: solid 1px; margin: 1rem; padding: 0.5rem; width: 15rem;">
			<div style="text-align:right;">
				<span style="float: left;">R1 Value:</span>
				<span id="r1-value" style="width:3rem;" />-</span>
			</div>
			<div style="text-align:right;">
				<span style="float: left;">R2 Value:</span>
				<span id="r2-value" style="width:3rem;" />-</span>
			</div>
			<div style="text-align:right;">
				<span style="float: left;">Zener Voltage:</span>
				<span id="zener-value" style="width:3rem;" />-</span> v
			</div>
		</div>

		<div style="border: solid 1px; margin: 1rem; padding: 0.5rem; width: 15rem;">
			<div style="text-align:right;">
				<span style="float: left;">Actual Max Current:</span>
				<span id="actual-current" style="width:3rem;" />-</span> mA
			</div>
			<div style="text-align:right;">
				<span style="float: left;">Actual Max ADC Voltage:</span>
				<span id="actual-vmax" style="width:3rem;" />-</span> v
			</div>
			<div style="text-align:right;">
				<span style="float: left;">Actual Min ADC Voltage:</span>
				<span id="actual-vmin" style="width:3rem;" />-</span> v
			</div>
		</div>
		<div style="border: solid 1px; margin: 1rem; padding: 0.5rem; width: 15rem;">
			<div style="text-align:right; width:100%">
				<span style="float: left;">ADC Resolution:</span>
				<select id="adc-bits" onchange="updateADC();">
					<option value="8">8-bit</option>
					<option value="10">10-bit</option>
					<option value="12">12-bit</option>
					<option value="16">16-bit</option>
				</select>
			</div>
			<div style="text-align:right;  width:100%">
				<span style="float: left;">ADC Max Value:</span>
				<span id="adc-valmax" style="width:3rem;" />-</span>
			</div>
			<div style="text-align:right;  width:100%">
				<span style="float: left;">ADC Min Value:</span>
				<span id="adc-valmin" style="width:3rem;" />-</span>
			</div>
		</div>
	</div>
	</div>
	<div style="float:left;">
		<img src="arduino-battery-sensing.png" />
	</div>

</form>
<script>
  // resistor values using a standard E12 series (10% resistance)
  // taken from https://eepower.com/resistor-guide/resistor-standards-and-codes/resistor-values/
  resistor_series_info = [
	{text: "E6   (±20%)", value:6, decade: [10,15,22,33,47,68]},
	{text: "E12  (±10%)", value:12, decade: [10,12,15,18,22,27,33,39,47,56,68,82]},
	{text: "E24  (±1%/±5%)", value:24, decade: [10,11,12,13,15,16,18,20,22,24,27,30,33,36,39,43,47,51,56,62,68,75,82,91]},
	{text: "E48  (±2%)", value:48, decade: [100,105,110,115,121,127,133,140,147,154,162,169,178,187,196,205,215,226,237,249,261,274,287,301,316,332,348,365,383,402,422,442,464,487,511,536,562,590,619,649,681,715,750,787,825,866,909,953]},
	{text: "E96  (±1%)", value:96, decade: [100,102,105,107,110,113,115,118,121,124,127,130,133,137,140,143,147,150,154,158,162,165,169,174,178,182,187,191,196,200,205,210,215,221,226,232,237,243,249,255,261,267,274,280,287,294,301,309,316,324,332,340,348,357,365,374,383,392,402,412,422,432,442,453,464,475,487,499,511,523,536,549,562,576,590,604,619,634,649,665,681,698,715,732,750,768,787,806,825,845,866,887,909,931,953,976]},
	{text: "E192 (±0.5%)", value:192, decade: [100,101,102,104,105,106,107,109,110,111,113,114,15,117,118,120,121,123,124,126,127,129,130,132,133,135,137,138,140,142,143,145,147,149,150,152,154,156,158,160,162,164,165,167,169,172,174,176,178,180,182,184,187,189,191,193,196,198,200,203,205,208,210,213,215,218,221,223,226,229,232,234,237,240,243,246,249,252,255,258,261,264,267,271,274,277,280,284,287,291,294,298,301,305,309,312,316,320,324,328,332,336,340,344,348,352,357,361,365,370,374,379,383,388,392,397,402,407,412,417,422,427,432,437,442,448,453,459,464,470,475,481,487,493,499,505,511,517,523,530,536,542,549,556,562,569,576,583,590,597,604,612,619,626,634,642,649,657,665,673,681,690,698,706,715,723,732,741,750,759,768,777,787,796,806,816,825,835,845,856,866,876,887,898,909,920,931,942,953,965,976,988]}
  ];

  resistor_values = [];
  
  zener_values = [
	  2, 2.2, 2.4, 2.7, 
	  3, 3.3, 3.6, 3.9, 
	  4.3, 4.7, 
	  5.1, 5.6, 
	  6.2, 6.8, 
	  7.5, 8.2, 9.1, 
	  10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 39
  ];
  
// ---------------------------------------------------------------------------  
  function calculate() {  
	VoltageHigh =  parseFloat(document.getElementById('bat-max').value);
	VoltageLow =  parseFloat(document.getElementById('bat-min').value);
	AdcHigh =  parseFloat(document.getElementById('adc-max').value);
	AdcLow =  parseFloat(document.getElementById('adc-min').value);
	VoltageZener = parseFloat(document.getElementById('zener').value);
	TargetCurrent = parseFloat(document.getElementById('current').value);
	
	// initial calculations
	VoltageRange = VoltageHigh - VoltageLow;
	VoltageOffset = VoltageHigh - AdcHigh;
	OffsetVoltageHigh = Math.max((VoltageHigh - VoltageZener), 0);
	OffsetVoltageLow = Math.max((VoltageLow - VoltageZener), 0);
	TargetResistanceTotal = OffsetVoltageHigh / (TargetCurrent / 1000);
	TargetResistanceR2 = TargetResistanceTotal * (AdcHigh / OffsetVoltageHigh);
	TargetResistanceR1 = TargetResistanceTotal - TargetResistanceR2;
	
	// build the resistor values array (up to 10M ohm)
	updateResistorValues();
	
	// find the closest resistors
	reducer = function(acc, v, i) {
		if (typeof acc === 'number') acc = {value: 0, diff: Infinity, idx: -1};
		let currentDiff = Math.abs(this - v);
		if (currentDiff < acc.diff) {
			return {
				value: v,
				idx: i,
				diff: currentDiff
			};
		} else {
			return acc;
		}
	};
	resistor_match_R2 = resistor_values.reduce(reducer.bind(TargetResistanceR2), 0);
	resistor_match_R1 = resistor_values.reduce(reducer.bind(TargetResistanceR1), 0);
	
	// calculate the actual performance of the circuit
	console.dir(resistor_match_R1);
	console.dir(resistor_match_R2);
	ActualVoltageHigh = (resistor_match_R2.value / (resistor_match_R2.value + resistor_match_R1.value)) * OffsetVoltageHigh;
	ActualVoltageLow = (resistor_match_R2.value / (resistor_match_R2.value + resistor_match_R1.value)) * OffsetVoltageLow;
	ActualCurrent = (OffsetVoltageHigh / (resistor_match_R2.value + resistor_match_R1.value)) * 1000;
	
	// display results
	document.getElementById('actual-vmax').innerHTML = ActualVoltageHigh.toFixed(3);
	document.getElementById('actual-vmin').innerHTML = ActualVoltageLow.toFixed(3);
	document.getElementById('actual-current').innerHTML = ActualCurrent.toFixed(3);	


	document.getElementById('r1-value').innerHTML = displayResistorValue(resistor_match_R1.value);
	document.getElementById('r2-value').innerHTML = displayResistorValue(resistor_match_R2.value);
	document.getElementById('zener-value').innerHTML = VoltageZener;
	
	
	// warn if clipping occurs because of high zener value
	if (VoltageLow < VoltageZener) {
		document.getElementById('actual-vmin').style.color = "red";
		document.getElementById('zener').style.borderColor = "red"
		document.getElementById('bat-min').style.borderColor = "red";
		if (VoltageHigh < VoltageZener) document.getElementById('bat-max').style.borderColor = "red";
	} else {
		document.getElementById('actual-vmin').style.color = "";
		document.getElementById('zener').style.borderColor = ""
		document.getElementById('bat-min').style.borderColor = "";
		document.getElementById('bat-max').style.borderColor = "";
	}
	
	updateADC();
  }
  
// ---------------------------------------------------------------------------  
	function updateADC() {
		ADCBits = parseInt(document.getElementById('adc-bits').value);
		ADCRange = 2 ** ADCBits - 1;
		ADCRangeHigh = Math.min((ADCRange - 1), parseInt(ADCRange * (ActualVoltageHigh / AdcHigh)));
		ADCRangeLow = Math.max(0, parseInt(ADCRange * (ActualVoltageLow / AdcHigh)));

		// display results
		document.getElementById('adc-valmax').innerHTML = ADCRangeHigh;
		document.getElementById('adc-valmin').innerHTML = ADCRangeLow;

		// warn that MCU will get above spec'ed voltage
		if (ActualVoltageHigh > AdcHigh) {
			document.getElementById('adc-valmax').style.color = "red";
			document.getElementById('actual-vmax').style.color = "red";
			document.getElementById('adc-max').style.borderColor = "red";
		} else {
			document.getElementById('adc-valmax').style.color = "";
			document.getElementById('actual-vmax').style.color = "";
			document.getElementById('adc-max').style.borderColor = "";
		}
	}

// ---------------------------------------------------------------------------  
	function populateZener() {
		let zenerEl = document.getElementById('zener');
		while (zenerEl.children.length) zenerEl.removeChild(zenerEl.children[0]);
		let tempNode = document.createElement('option');
		tempNode.text = "-none-";
		tempNode.value = "0";
		zenerEl.appendChild(tempNode);
		for (let val of zener_values) {
			if (val > parseFloat(document.getElementById('bat-min').value)) break;
			tempNode = document.createElement('option');
			tempNode.text = val + " v";
			tempNode.value = val;
			zenerEl.appendChild(tempNode);
		}		
	}

// ---------------------------------------------------------------------------  
	function populateResistorSeries() {
		let resistorsEl = document.getElementById('resistor-series');
		while (resistorsEl.children.length) resistorsEl.removeChild(resistorsEl.children[0]);
		let tempNode;
		for (let val of resistor_series_info) {
			tempNode = document.createElement('option');
			tempNode.text = val.text;
			tempNode.value = val.value;
			resistorsEl.appendChild(tempNode);
		}
		// select E12 as default
		resistorsEl.value = "12";
	}

// ---------------------------------------------------------------------------  
	function updateResistorValues() {
		resistor_values = [];
		series_value = parseInt(document.getElementById('resistor-series').value);
		series_decade = resistor_series_info.filter((x) => x.value === series_value)[0].decade;
		let decade = 0.1;
		if (series_decade[0] === 100) decade = 0.001;
		let last_resistor = 0;
		while (last_resistor < 100000000) {
			for (let entry of series_decade) {
				last_resistor = decade * entry;
				resistor_values.push(parseFloat(Intl.NumberFormat('en-US',{maximumSignificantDigits: 2}).format(last_resistor).replaceAll(',','')));
			}
			decade = decade * 10;
		}
		console.dir(resistor_values);
	}


// ---------------------------------------------------------------------------  
	function displayResistorValue(value) {
		let temp = value + "";
		let ohm = "Ω";
		switch (String(value).length) {
			case 4: 
			case 5: 
			case 6:
				ohm = "K" + ohm;
				value = value / 1000;
				break;
			case 7: 
			case 8: 
			case 9:
				ohm = "M" + ohm;
				value = value / 1000000;
				break;
		}
		return value + " " + ohm;
	}


// ---------------------------------------------------------------------------  
populateResistorSeries();


</script>
</body>
</html>