CalcHowTo
From CunningWiki
Intro
As an electrial engineer I spent a lot of time using and creating excel based calculators. The problem I have is when I or other people make minor changes we rarely ever syncronize our updatse. Eventually we just redesign the calculators from scratch. To try and reduce time I wanted to create them in javascript on a webpage. That way I know I can access it anywhere and update it on any pc.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD><TITLE>Current Limiting Resistor Calculator</TITLE>
<SCRIPT language=JavaScript>
function Compute1(form) {
with(Math) {
var Precision= 0;
var Vin= Number(form.Vin.value);
var Vled= Number(form.Vled.value);
var Iled= Number(form.Iled.value);
Rled= (Vin-Vled)/(Iled/1000);
Wresistor= (Vin-Vled)*(Iled/1000);
if(Rled<0) {
alert("the numbers you entered don't make sense!!!");
}
form.Rled.value= Rled.toFixed(Precision);
Precision= 3;
form.Wresistor.value= Wresistor.toFixed(Precision);
}
}
</SCRIPT>
<META name=GENERATOR content="MSHTML 8.00.6001.19154"></HEAD>
<FORM method=post name=ParamForm action="">
<TABLE border=1>
<TBODY>
<TR>
<TD colSpan=2>
<P align=center><FONT face=Arial><B>LED Current Limiting Resistor Calc</B></FONT></P></TD></TR>
<TR>
<TD><FONT size=3 face=Arial>Voltage Input</FONT></TD>
<TD><FONT face=Arial><INPUT value=5 size=17 name=Vin> (V)</FONT></TD></TR>
<TR>
<TD><FONT face=Arial>LED Voltage</FONT></TD>
<TD><FONT face=Arial><INPUT value=2.1 size=17 name=Vled> (V)</FONT></TD></TR>
<TR>
<TD><FONT face=Arial>LED Current</FONT></TD>
<TD><FONT face=Arial><INPUT value=20 size=17 name=Iled> (mA)</FONT></TD></TR>
<TR>
<TD colSpan=2>
<P align=center><FONT face=Arial><B>Results</B></FONT></P></TD></TR>
<TR>
<TD><FONT face=Arial>Current Limiting Resistor<BR><INPUT size=17 name=Rled>(Ohms)<BR><INPUT onclick=Compute1(document.ParamForm) value="Submit" type=button></FONT></TD>
<TD><FONT face=Arial>Resistor Power rating<BR><INPUT size=17 name=Wresistor>(Watts)<BR></FONT></TD>
</HTML>
