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<head><title>DTMFOUT</title>
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<h1 class="code">DTMFOUT</h1>
<div class="ImagePlusCaption">
<div class="Col2">
<p>
<img src="../../graphics/pgm_icon2.gif" border="0" alt="BS2 icon" title="BS2 icon" />
<img src="../../graphics/pgm_icon2e.gif" border="0" alt="BS2e icon" title="BS2e icon" />
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<p style="text-align: right;"><a href="../ExampleTopics/DtmfoutEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">DTMFOUT Example</a>
</p>
<p>&#160;</p>
</div>
<p class="clear">&#160;</p>
<p>&#160;</p>
<p class="PlainText">Syntax: <span class="keyword_in_text">DTMFOUT</span> <![CDATA[ ]]><i>Pin</i>, {<i>OnTime</i>,<i> OffTime</i>,} [<i>Tone
</i>{,<i> Tone...</i>}]</p>
<h2>Function</h2>
<p class="PlainText">Generate dual-tone, multi-frequency tones (DTMF, i.e., telephone "touch" tones).
</p>
<ul>
<li value="1"><b><i>Pin</i></b> is a variable/constant/expression (0 - 15) that specifies
the I/O pin to use. This pin will be set to output mode during generation of
tones and set to input mode afterwards.</li>
<li value="2"><b><i>OnTime</i></b> is an optional variable/constant/expression (0 - 65535)
specifying a duration of the tone. The unit of time and the default time for
<i>OnTime</i> is described below. </li>
<li value="3"><b><i>OffTime</i></b> is an optional variable/constant/expression (0 - 65535)
specifying the length of silent pause after a tone (or between tones, if
multiple tones are specified). The unit of time and the default time for
<i>OffTime</i> is described below.</li>
<li value="4"><b><i>Tone</i></b> is a variable/constant/expression (0 - 15) specifying the
DTMF tone to generate. Tones 0 through 11 correspond to the standard layout
of the telephone keypad, while 12 through 15 are the fourth-column tones used
by phone test equipment and in ham-radio applications. </li>
</ul>
<h2>Quick Facts<br /></h2>
<table width="100%" cellpadding="4" cellspacing="0" border="1">
<tr>
<td width="20%" align="center" bgcolor="#CFCFCF">&#160;</td>
<td width="16%" align="center" bgcolor="#CFCFCF">BS2 / BS2e</td>
<td width="16%" align="center" bgcolor="#CFCFCF">BS2sx</td>
<td width="16%" align="center" bgcolor="#CFCFCF">BS2p</td>
<td width="16%" align="center" bgcolor="#CFCFCF">BS2pe</td>
<td width="16%" align="center" bgcolor="#CFCFCF">BS2px</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Default <i>OnTime</i></td>
<td align="center">200 ms</td>
<td align="center">80 ms</td>
<td align="center">55 ms</td>
<td align="center">196 ms</td>
<td align="center">34 ms</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Default <i>OffTime</i></td>
<td align="center">50 ms</td>
<td align="center">50 ms</td>
<td align="center">50 ms</td>
<td align="center">50 ms</td>
<td align="center">50 ms</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Units in <i>OnTime</i></td>
<td align="center">1 ms</td>
<td align="center">0.4 ms</td>
<td align="center">0.265 ms</td>
<td align="center">1 ms</td>
<td align="center">0.166 ms</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Units in <i>OffTime</i></td>
<td align="center">1 ms</td>
<td align="center">1 ms</td>
<td align="center">1 ms</td>
<td align="center">1 ms</td>
<td align="center">1 ms</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Related Commands</td>
<td align="center" colspan="5">
<p colspan="5" align="center"><a href="SOUND.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">SOUND</a>,&#160; <a href="FREQOUT.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">FREQOUT</a></p>
</td>
</tr>
</table>
<h2>Explanation</h2>
<p class="PlainText">DTMF tones are used to dial the phone or remotely control certain radio equipment.
The BASIC Stamp can generate these tones digitally using the <span class="keyword_in_text">DTMFOUT</span>
instruction. </p>
<p class="PlainText">This figure shows how to connect an audio amplifier or speaker to hear these
tones:</p>
<center>
<img src="../../graphics/freqout_sch.gif" border="0">
</img>
</center>
<p class="PlainText">...and this figure shows how to connect the BASIC Stamp to the phone line:</p>
<center>
<img src="../../graphics/daa_sch.gif" border="0">
</img>
</center>
<p class="PlainText">The following <span class="keyword_in_text">DTMFOUT</span> instruction will generate DTMF tones on I/O pin 0:
</p><pre class="BScode" xml:space="preserve">
' Call Parallax
DTMFOUT 0, [1, 9, 1, 6, 6, 2, 4, 8, 3, 3, 3]
</pre>
<p class="PlainText">If the BASIC Stamp is connected to the phone line properly, the above command
would be equivalent to dialing 1-916-624-8333 from a phone keypad. If you wanted
to slow the pace of the dialing to accommodate a noisy phone line or radio link,
you could use the optional <i>OnTime</i> and <i>OffTime</i> values:
</p><pre class="BScode" xml:space="preserve">
' Call Parallax; dial slowly.
DTMFOUT 0, 500, 100, [1, 9, 1, 6, 6, 2, 4, 8, 3, 3, 3]
</pre>
<p>In this example, on a BS2 the<i>OnTime</i> is set to 500 ms (1/2 second) and <i>OffTime</i> to 100 ms (1/10th second).</p>
<p>&#160;</p>
<center>
<table cellpadding="4" cellspacing="0" border="1">
<tr>
<td align="center" width="75" bgcolor="#CFCFCF">Tone Value</td>
<td align="center" width="250" bgcolor="#CFCFCF">Corresponding Telephone Key</td>
</tr>
<tr>
<td align="center">0 - 9</td>
<td align="center">Digits 0 through 9</td>
</tr>
<tr>
<td align="center">10</td>
<td align="center">Star (*)</td>
</tr>
<tr>
<td align="center">11</td>
<td align="center">Pound (#)</td>
</tr>
<tr>
<td align="center">12 - 15</td>
<td align="center">Fourth column tones A through D</td>
</tr>
</table>
</center>
<p class="PlainText">&#160;</p>
<p class="PlainText">The BASIC Stamp microcontroller is a purely digital device. DTMF tones are analog
waveforms, consisting of a mixture of two sine waves at different audio frequencies.
So how does a digital device generate analog output? The BASIC Stamp creates and
mixes the sine waves mathematically, then uses the resulting stream of numbers to
control the duty cycle of a very fast pulse-width modulation (PWM) routine. So
what's actually coming out of the I/O pin is a rapid stream of pulses. The purpose
of the filtering arrangements shown in the figures above is to smooth out the
high-frequency PWM, leaving only the lower frequency audio behind. </p>
<p class="PlainText">Keep this in mind if you want to interface a BASIC Stamp module's DTMF output to radios
and other equipment that could be adversely affected by the presence of
high-frequency
noise on the input. Make sure to filter the DTMF output thoroughly. The circuits
above are only a starting point; you may want to use an active low-pass filter
with a roll-off point around 2 kHz.</p>
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<p style="text-align: right;"><span class="ContactInfoProjectName">BASIC Stamp Help</span> <![CDATA[ ]]><span class="ContactInfoVersion#">Version 2.5.4</span> <![CDATA[ ]]></p>
<p style="text-align: right;">Copyright ©&#160;<span class="ContactInfoCompanyName">Parallax Inc.</span></p>
<p style="text-align: right;"><span class="SystemShortDate">8/8/2012</span>
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