Interfacing the UV5R with a Raspberry PI 3 Echolink-Svxlink

Posted on May 7, 2017
Filed Under Amateur Radio | Leave a Comment

Today’s post is about my successfully interfacing a UV5R Baofeng with a Raspberry PI 3 running Svxlink.  Primary use is for an Echolink node connecting to a local repeater.

My primary goal was to NOT use VOX to trigger the push to talk but to use a COS or Carrier Operated Switch.

Svxlink is a powerful software program that can be used as a repeater controller, a simplex link. Supports networked multiple receivers and transmitters. It also has an Echolink module.

Echolink is a popular system that allows two or more nodes to connect over the internet.

I wont discuss the installation or setup of Svxlink as that is covered many times. Svxlink has built in support of the GPIO (General Purpose Input Output) pins  on a Raspberry PI.

During my research time and time again I found reference to a hardware modification for the UV5R where you solder a wire to pin 2 of the audio amplifier in the UV5R.

The final audio amplifier’s supply voltage is removed when no signal is present and supplied when signals are received. This mod which connects to that supply Vcc was fairly easy and can be found here.

However I noticed on the schematic of the UV5R that there is no dc blocking capacitor on output to the speaker and external speaker jack.  The output goes to about 3 volts when the amplifier is enabled. To zero when no signal is received. Why then do I need to open the case?

 

UV5R audio output section

It is not necessary. Note the connection from pin 1 to the external speaker jack. Seems like a poor design to me to keep the internal speaker inline? (I wont go into the point of C158 and R192 in series with ground connect at each end? The schematic *must* be wrong..    At least their is 3 volts on the external speaker output when a signal is present…I can work with that!!

Here is the interface I built which works fine.  It expects the PTT control signal from the GPIO pin to go high (3v) to trigger the ptt output which grounds the PTT line from the UV5R.  And the COS signal to go hi (3v) from the RX when a signal is received. The output will also go hi when is connected to one of the GPIO pins on the Raspberry PI.

I decided to use 2 1:1 isolation transformers for the audio to minimize hum. I also am using two pc817 opto isolators instead of relays for outputs for the COS signal and PTT.

There are three adjustments. RX audio level, TX audio level and the COS/COR threshold. I made that variable so it can be used on other systems if desired.

Audio / digital interface for echolink for UV5R and Raspberry PI

 

 

 

 

 

 

 

 

Here is the first version of the circuit.

Completed interface board.

 

 

 

 

 

 

The main take-away here is NO NEED to MODIFY the UV5R.

This circuit can also be used to interface with a PC serial port *however* you might want to add a diode on the PTT input to prevent rs-232 negative voltages. And you don’t have to use 3.3v unless you are interfacing with logic that requires 3.3v.

I hope this helps some struggling Amateur. Feel free to use/modify etc to suit your purposes.

All parts were ordered on Amazon and the total cost is about $10. Hard to tell as I purchased the parts in lots of 10 or more.

73 WB5HUP

 

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