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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>3.2.  Converting between integer data and physical units</title><link rel="stylesheet" type="text/css" href="comedilib.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="index.html" title="Comedi"><link rel="up" href="writingprograms.html" title="3.  Writing Comedi programs"><link rel="prev" href="writingprograms.html" title="3.  Writing Comedi programs"><link rel="next" href="secondprogram.html" title="3.3.  Your second Comedi program"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">3.2. 
Converting between integer data and physical units
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Writing <acronym class="acronym">Comedi</acronym> programs
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Converting between integer data and physical units
</h3></div></div></div><p>
If you selected an analog input subdevice, you probably noticed
that the output of <span class="command"><strong>tut1</strong></span> is an unsigned
number, for example between <code class="literal">0</code>
and <code class="literal">65535</code> for a 16 bit analog input. <a class="ulink" href="http://www.comedi.org" target="_top"><acronym class="acronym">Comedi</acronym></a>
samples are unsigned, with <code class="literal">0</code> representing the
lowest voltage of the ADC, and a hardware-dependent maximum
value representing the highest voltage. <a class="ulink" href="http://www.comedi.org" target="_top"><acronym class="acronym">Comedi</acronym></a> compensates
for anything else the manual for your device says (for example,
many boards represent bipolar analog input voltages as signed
integers). However, you probably prefer to have this number
translated to a voltage. Naturally, as a good programmer, your
first question is: <span class="quote">“<span class="quote">How do I do this in a
device-independent manner?</span>”</span>
</p><p>
The functions
<code class="function"><a class="link" href="func-ref-comedi-to-physical.html" title="comedi_to_physical">comedi_to_physical</a></code>, <code class="function"><a class="link" href="func-ref-comedi-to-phys.html" title="comedi_to_phys">comedi_to_phys</a></code>,
<code class="function"><a class="link" href="func-ref-comedi-from-physical.html" title="comedi_from_physical">comedi_from_physical</a></code> and <code class="function"><a class="link" href="func-ref-comedi-from-phys.html" title="comedi_from_phys">comedi_from_phys</a></code>
are used to convert between <a class="ulink" href="http://www.comedi.org" target="_top"><acronym class="acronym">Comedi</acronym></a>'s integer data and floating point numbers corresponding
to physical values (voltages, etc.).
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Writing <acronym class="acronym">Comedi</acronym> programs
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Your second <acronym class="acronym">Comedi</acronym> program
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