Questions about interfacing to Baofeng

[bettio]

Nice project, I was looking into doing something similar.
The schematics I found so far for interfacing with the Baofeng were quite different, the most important difference was about the PTT that was implemented using an audio transformer component rather the solution in your project.
Did you test also test also the audio transformer solution? Are you aware of any pro of using the tansformer rather than your solution?

[dalethomas81]

In this project, I am using the same method as the MicroAPRS (which is also where the modem firmware is from). I have not tested any other design. Can you link an example?

[bettio]

Can you link an example?

Sure: https://k0rx.com/blog/2017/11/baofeng.html

[dalethomas81]

The PTT interface in this example is not implemented using an audio transformer. That is for the audio input (PC->Baofeng).

The PTT interface in this example is implemented using an optocoupler. Which is a very good idea. Basically, with an optocoupler the circuits are completely isolated. The driving circuit turns on a LED whereas the driven circuit detects the LED with a photo-resistor.

Thank you for the article. I would like to see the performance difference in the optocoupler versus the BJT method that HamMessenger is using.

[bettio]

In your opinion, does using an audio transformer for the audio input gives any relevant advantage over the MicroAPRS board design?

[dalethomas81]

Using the audio transformer requires that you have an actual sound card. In other words a DAC (digital to analog converter).

The Arduino does not so the way the MicroAPRS is doing it is required. It uses several digital outputs to simulate a sound wave. I suppose you could add the audio transformer in addition to it though I don't know what benefit that would get you.

If you do experiment with this, please let me know the results.

I am thinking with the next iteration of the board, I may try the optocoupler design in the circuit you referenced. Would be good to experience with that vs the BJT as well.

[srem1]

baofeng is baned in many county for example poland, You must have ham licence.
look at http://www.whence.com/minimodem/
or rattlegram (Android program)
etc.