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Background:
There are some things that don't seem to be explained very well when building a radio less node. This dissertation attemps to change that. I apologize up front - it's long, but I feel it's necessary.

When you use a radio adapter interface like the RL-20 for a radio-less node, things end up a little backwards as compared to when connecting a radio. When you build a radio-less node, the PTT logic that's generated isn't used for anything - there's no radio to key. When I know someone is using the RL-20 in a radio-less application, I give them the option of not installing the DB9 and the the RED and Yellow LEDs. Or - installing the two LEDs in their opposite positions as it ends up making more sense. I'll try to explain this all below...

Explanation:
In order to tell the node you are "transmitting", you'll depress the PTT button on the MIC. The logic created by the PTT switch in the microphone will ground the COS logic line (pin 3 on the DB9). CTCSS logic isn't required since the depression of the PTT switch on the MIC is all that's necessary to key up the node. As such nothing is connected to the CTCSS logic input at DB9 pin 4, and you'll not configure the node to use CTCSS in the ASL software.

The Alinco EMS-57 MIC referenced in several online articles is a good choice for this application. To make the microphone work properly, you need to supply voltage to it. This requires a power source, and the 5V supply running the Pi/radio interface is sufficient for the microphone too. You can supply voltage to the MIC from the +5 volt point on the RL-20 from the hole marked MIC +5V on the silkscreen. You'll obviously need to figure out the microphone's pin-out so you can wire things up correctly. The pot on the RL-20 becomes "MIC GAIN" in a radio-less application - instead of RX audio.

The RL-20 doesn't produce enough audio to drive a speaker to a very loud volume, and there's no rotational volume control. You'll probably want to wire a speaker amplifier to DB9 pin 1 or 2, (most times pin 2 - depending on which one is selected in the channel driver). You'll want to wire in a volume control so you can adjust the loudness of the speaker. The audio output is referenced to ground - the same ground the microphone is referenced to - - as well as the power ground. Remember to set the loudness to a sufficient level in software, so the volume control is nice and smooth, not all "one ended" if the audio it too hot coming out of the CM119A. This is done in the HamVoIP software. There are small Class-D audio amps that will additionally run from the 5V on the RL-20. On the latest version of the circuit board, a connection to +5V is provided for the audio amplifier from the hole marked "AUDIO AMP +5V on the silkscreen. Just make sure you use a power supply capable of the current draw. Something with 2-3 amps usually works well.

Additionally - here's an article you can reference about building a radio-less node that follows the outline suggested here.

Some extra steps that aren't required but are really nice:
COS Activity Indication (or radio-less PTT indication):
By asserting a change on one of the GPIO on the CM119A, the LED3 position can indicate receiver activity (COS) or local PTT by following the software status of the COS logic input. Some code is necessary to make this work and is different for HamVoIP and AllStarLink. Examples for both are included below.

When used as a radio adapter, the status of the COS can be shown with an onboard Yellow LED3. When used as a radio-less interface it's common to swap the positions of LED1 and LED3, the Red and Yellow LED's. Then - local PTT is indicated by the Red LED3 and netwrok activity is indicated by the Yellow LED1. In this role, think of the Yellow LED as a "busy" light on a radio. LED3 is driven from a CM119A GPIO when commanded to do so in software.

In HamVoIP this code is necessary to make the LED3 option work.

In AllStarLink this code is necessary to make the LED3 option work.

Since you are making a radio-less node, the COS logic input is sourced from the PTT action of the Microphone. As such - illumination of LED3 now follows the action of the PTT switch. Since this function is now PTT (and no longer COS) - putting the RED LED in position 3 makes more sense.
This is why I install the RED LED into position LED3 - for this type of application.

LED1's location is no longer PTT. It now becomes a "BUSY" indicator, showing when there is remote activity on the node. Now, the only thing the PTT circuitry on the RL-20 does - is illuminates LED1's position.
This is why I install the Yellow LED into position LED1 - for this type of application.

Location LED1 and LED3 has alternate silkscreen descriptions. Those inside the *asterisk's* are for radio-less installations.

Hope this helps...

Email Kevin Custer for support.
 

Custom cables available from URI Cables. They will build a custom cable for the RL-20 for many radios.

Article by Kevin Custer W3KKC.

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Board layout by Kevin Custer W3KKC
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