Developing a universal module

My original design was an encoded 4-way analog multiplexer which had 2 selects and a 3rd signal wire. It worked fine, but there are a few drawbacks:
1) you can only control the CS pin. If you want to control CE or Reset or any other pin, you are out of luck.
2) you need 3 wires, which means you either need to use the Cyrf 'Reset' wire, or you need to hold the CYRF chip in REset while using the CSn wire. Neither is ideal.

I also considered using a 2:4 decoder which would do the same with only 2 wires, but only supports 3 modules ('00' needs to be used to shut all modules off), or uses a 3rd disable signal (in which case the analog mux is superior)

The AVR actually has fewer pins than the other options, only needs 1 extra wire for control (after programming), and provides 7 controllable pins, allowing the use of CE and Reset, or PA/LNA enables as needed.

I've seen a lot of different proposals, but have not yet seen one which requires a smaller package, fewer parts, is significantly less expensive, or provides any significant advantage over the current design.

The only significant drawback to the current approach is that it requires programming. I negate that by using the Tx itself for programming so that no additional hardware is needed. A second potential issue is that it limits maximum transfer rate due to how fast the AVR can react to a CSn change, but that isn't an issue in practice.

There is no reason you can't get 4 wires into a hollow antenna. Of course, some of the Devo radios use a screw-on antenna instead, and for those, you are out of luck.

PhracturedBlue wrote: There is no reason you can't get 4 wires into a hollow antenna. Of course, some of the Devo radios use a screw-on antenna instead, and for those, you are out of luck.

I would debate on this, since even a passive conductive wire has strong effect on any antenna system. Just think about the yagi antenna which is one dipole and a few passive reflectors, and you've got a highly modified radiation pattern...

Fair enough. I'm going to bet that no one can demonstrate any practical impact on range by placing 4 antennas in one sheath with Deviation.

If you can (and I can reproduce it), I'll donate a fully built universal module

I am not taking orders. We'll cross that bridge when we come to it.

FYI, I had considered making a module which used a more capable CortexM cores (like the Teensy3.0). By replacing the AVR with a Teensy3.0 module, you could have a universal module with both PPM and SPI. And it could run our protocol stack out of the box. I haven't looked at Midelic's code, but every Arduino solution I've seen (which uses our protocol code) has ended up significantly modifying it to run on Arduino. I don't understand why to be honest, as it means more work for everyone because bug fixes can't easily move between projects.

The main problem is protocol selection, and I've yet to see a good solution for an external module. When using Deviation, we could use a special PPM train to send digital data, but in that case, might as well use SPI which is far superior. When using a closed-source Tx, you'd need to either have switches on the back, or use some stick input to control it. You also end up wanting some sort of display of the current protocol selected, and then some way to input parameters, and ... Now you've got a large, expensive module (and it still can't reliably do telemetry). The way I've gone, Deviation gets all the benefits we want at the lowest cost I can achieve. If someone else wants to hook up a PPM to SPI converter (which I think th9xr is also working on), that's cool, but it isn't my project.