Amateur radio PPT function

[ImageJPEG]

Hello everyone! I've owned a Raspberry Pi B+ for a few years now and I've never really done anything with it.

I've been a licensed ham for just over a year now. I've been getting very interested in APRS and packet radio, both of which would require a computer controlling the push to talk function on the radio.

Most people use a USB to 9 pin serial adapter. I would like to get rid of that mess and try to use the gpio to do the same function.

I've got most of my information from this site: http://www.marcelpost.com/wiki/index.ph ... rigger_PTT

However, looking at the pictures at the bottom seem to be over complicated with the MOSFETs being used...plus he's using the 3.3 volt which iirc is current limited with the gpio.

My idea is to instead use the 5 volt supply, which iirc, is current limited to the USB power supply.

I want to put the 5 volts through a 3.3v linear voltage regular then into the emitter of a PNP transistor. Gpio pin 17 would go into the base (according to the site listed above, pin 17 is RTS which would be high when not activating the PPT and low when activated). Finally, the collector would go into an optoisolator. The optoisolator, when turned on would allow the ptt circuit to ground out, allowing the radio to start transmitting.

After the optoisolator on the Pi's side, an LED would be placed to indicate that the radio is transmitting.

This would be my first electronics project and I just want some suggestions with how I can make this better and if there's anything hugely wrong with my design.

[mahjongg]

any method where you can light a LED (of an opto-isolator) under software control will do.
There must be thousands of examples you can google for.

just adhere to one rule, while experimenting, and that is that under no circumstance you should put 5 Volt (or more, or negative voltages) on any GPIO pin, the PI's GPIO pins are not 5V tolerant!

[ImageJPEG]

I would assume that since I'm putting 5 volts through a 3.3 regulator, my setup would be fine then.

Also, how can I go about software controlling an optoisolator? I'm lost on that :/

[paulie]

I use APRS on Pi:
I currently use two methods for implementing TNCs, TNC-Pi (a hardware kit by John W2FS), and a USB soundcard. Software for the soundcard is direwolf, which gives you the option of using a GPIO pin for PTT.

[ImageJPEG]

I'm wanting to use the Pi as the TNC. I've looked up about soundmodem and xastir.

If I choose the direwolf method, do I still need to change the gpio mappings?

[mahjongg]

Also, how can I go about software controlling an optoisolator? I'm lost on that :/

Its just a LED, plenty of explanations given how to control a LED.

[ImageJPEG]

Sorry, I understand what you're talking about now. I was lost for a minute.