Shack in the Box: A 2m/70cm FM transceiver

This is a project that I started last year and, after a few weeks, lost interest in it until recently.

During my usual web snooping for interesting parts, I came across these VHF and UHF modules being sold by Nice RF in China.  About the size of three side-by-side postage stamps, each is a complete (except for the low-pass filter and audio power amp) transceiver for the VHF (136-174 MHz) and UHF (400-470 MHz) bands.  The modules are good for about a Watt output, and are programmed serially via a series of AT commands - perfect for interfacing to an Arduino!

The modules are the ultimate black-boxes and contain all of the RF, switching, demodulating, and CTCSS/DCS circuitry, so building this rig has been much more of an effort in programming than it has in building hardware, which is partly the reason that I lost interest in it last May; I had gotten stuck in how to program a few functions and temporarily burned-out.  But, after taking a break from it, I've been making good progress over the past few days.

One of my peeves about many 2m/70cm rigs is that they're not at all intuitive to operate.  My ancient Kenwood TR-7950, on the other hand, is a breeze; even someone unfamiliar with the radio could easily figure out how everything works on it, so I used that as my "model" for the user interface.

Basically, one can either enter the desired frequency via the keypad (VFO mode) or recall it from one of 16 memory channels, selected using the pot to the right of the display.  The display shows the frequency, repeater offset, tone frequency and mode, and also indicates whether the selected memory is in, or locked-out of, the scan list.

The keypad itself is a 16 switch matrix that I purchased from Ebay.  To conserve I/O, I've interfaced it to the Arduino via a resistor divider network, allowing it to be read using only one analog I/O pin.  Likewise, the memory selection is done using a pot and another analog I/O pin.

Serial communication between the Arduino and VHF/UHF modules is done using the "Soft Serial" libraries, which allows using other I/O pins for serial comms and keeps the UART free for programming/debugging.  

Not shown on the VERY INCOMPLETE schematic below is the LCD module, which talks to the Arduino over the I2C buss. 

Cosmetically, I've long been intrigued by the Paraset tranceivers that were provided to the resistance during WWII, so the vague resemblance isn't coincidental.

Obviously, this is still very much a work in progress, so I'll be posting a few follow-ups as things progress.  I just got this to the point to where I've made a few QSOs with it, so I wanted to share it in its raw, al fresco state.

Preliminary (very!) and incomplete schematic - for inspirational purposes only, do not duplicate!!!

 One may wonder why anyone would go through the trouble of building something like this when you can order something like a Baofeng for $30.  That's a valid question, and my answer is simple: Because I can!