There are many parts called RF module in the market but most of them cannot build a walkie talkie! There is a quicky to find one, please search CTCSS or DCS as keywords. These analog and digital squelch systems would stop the RF modules built for wireless voice communication.
If an RF module is with CTCSS and DCS built in, replacing it with a walkie talkie would be a piece of cake. The second consideration is the work band if that module can be forced to work on disc radio amateur bands, twin bands or even triband, congratulations!
I found that two Chinese companies sell these types of RF modules:
- NiceRF (www.nicerf.com) with 7 modules SA818, SA828, SA858, SA868 and DMR81
- Sunrise (www .sunrisedigit.com) with 4 modules: SR_FRS_1WU, SR_FRS_1WV, SR_FRS_2WU and SR_FRS_2WUS
What I use this project is SR_FRS_2WUS, here comes the simple pinout image and PDF document including the AT commands supported. Unfortunately, all documentation is in simplified Chinese. I have translated the Pinout chart and done my best to make comments on the sketch, ask me if you need more translations.
SR_FRS_2WUS is recommended to work at 400MHz to 470MHz but take advantage of the central chip used, AT1846S (RDA1846), we can force it to cover the 2m and 1.25m band as well. (According to the data sheet for AT1846S, the frequency range is as follows, see attached PDF files in step 14 for details.)
All pinout is very easy to understand except pin 6 and pin 11. Pin 6 is for controlling hardware output, but I have never done so. I was told by technicians when I asked for support, the function is set in the existing firmware version and we can only control the output through AT group command now. The pin 11 should be an output while the VOX is activated, but I didn't do it too. Actually, I really prefer an LED lamp while VOX is on and I am transmitting. VOX can be active at the command and works very well.
Pin17 out turns on my microphone and MCP41010 now makes the sound away from the digital noise generated from the MCU, compared to connecting them to the VCC of our Arduino Pro mini.