https://www.marcelpost.com/wiki/index.php?action=history&feed=atom&title=TNC-PiTNC-Pi - Revision history2026-05-17T04:58:52ZRevision history for this page on the wikiMediaWiki 1.39.17https://www.marcelpost.com/wiki/index.php?title=TNC-Pi&diff=2008&oldid=prevAdmin: /* =DB9 Pinout */2015-04-07T02:48:29Z<p><span dir="auto"><span class="autocomment">=DB9 Pinout</span></span></p>
<p><b>New page</b></p><div>APRS Terminal Node Controller for the Raspberry Pi<br />
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[[File:TNC-Pi.jpg|thumb|none|400px]]<br />
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==Circuit Board==<br />
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[[File:RPi-PCB top.jpg]]<br />
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[[File:RPi-PCB bottom.jpg]]<br />
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Bell 202 chip: MX614P<br />
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==MX614P output levels==<br />
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The audio output voltage seen on this chip is 1.4V peak-to-peak.<br />
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[[File:MX614P.jpg]]<br />
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==Output Volume==<br />
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Trimpot R7 controls the output volume of the TNC-Pi to your radio. It is a single-gang pot and has a range from 0V (fully counter-clockwise) to about 700mV (fully clockwise)<br />
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[[File:TNC-Pi R7.jpg]]<br />
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The output signals are generated from the MX614P chip. The Audio_OUT on this chip is on pin 7. At any frequency, the output level on this pin is about 1.4V peak-to-peak. This is true for the 487Hz resting tone and the 1200Hz/2200Hz AFSK tones.<br />
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==Input Volume==<br />
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The input volume to the TNC was not found in any documentation but through experiment I found that a input voltage range between 170mV - 300mV was effective in successfully decoding APRS packets.<br />
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==TXDelay==<br />
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The time between PTT-on and actual transmit of data can be set with R6 which controls the TX-Delay. At this stage I have no further information on the range or effectiveness of this trimpot.<br />
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[[File:TNC-Pi R6.jpg]]<br />
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==Radio Header==<br />
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The 4-pin socket (header probably missing) labeled 'radio' is to get easy access to the Audio, GND and PTT lines.<br />
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[[File:TNC-Pi radio header.png]]<br />
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==DB9 Pinout==<br />
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The DB9 Female connector on the TNC-Pi board is used to interface RX Audio, TX Audio and PTT to the transceiver. <br />
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The pinout is as follows:<br />
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[[File:TNC-Pi DB9-Female pinout.jpg]]<br />
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Looking at the solder side from a plug (DB9 Male) that fits into the above socket:<br />
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[[File:TNC-Pi DB9-Male solderside.jpg]]<br />
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TX Audio is the audio coming out of the TNC when transmitting and will go to the radio to be transmitted.<br />
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RX Audio is the received audio coming out of the radio that is going to the TCN<br />
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PTT (push to talk) is done by the TNC-Pi by tying it to GND. This then puts most receivers into transmit.</div>Admin