A brief update on 2.4 GHz radio add-ons for Teensy 3.1.
I thought the range of the first nRF24L01+ radio design I built with the ceramic antenna was not very good so I redesigned the board with an on-board antenna. One design used that recommended by Nordic, just a long, thick metal line. The other I shamelessly copied from the $3 Chinese boards I have been buying. I also made an adapter for these cheap boards so I can test them against my own in the same test rig. Unfortunately, I don't have an RF scope so I can't test the antenna gains and matching properly. I just did a qualitative test through walls and at distance in my house.
Here is what I am working with:
My two designs with two different pcb antennas on the left, the $3 competition on the right with the Teensy 3.1 adapter soldered into place. You can see in the second picture how the adapter mounts to the Teensy 3.1 in the same way the custom made boards do. It was rather difficult to solder the adapter into place; it's not a great design but I made it work.
I added headers to the boards so I could exchange them on the Teensy 3.1 test rig, which has the extra long machine pin headers from Schmartboard. In actual use I would just solder the boards directly to the Teensy, probably underneath.
I used the yaw output from the MAX21100 + LIS3MDL motion sensor suite as a transmit variable, and monitored receipt from the stationary test rig to a mobile battery-powered 3.3 V Pro Mini + nRF24L01+ with a display to tell when I lost the signal, etc. The remote broadcast a PWM thrust variable in exchange. Successful transmission was receipt of the yaw and confirmation of send of the thrust. That way I know the two radios are still talking to each other. It's clunky, but it works and mimics the real application; remote control of a motorized vehicle.
The weird thing is I didn't get any yaw value returned with the $3 version of the nRF24L01+ in its adapter when mounted to the Teensy 3.1 no matter how close it was to the receiver, but I did get verification that it was receiving the thrust transmission.
The custom made boards both reported yaw and confirmed thrust out to 40 feet with at least one wall between the sender and receiver. I couldn't really tell the difference between the two antenna performances; it looks like either one is better than the ceramic antenna I used previously. I prefer the Chinese design since it is smaller, and I think, looks more interesting than the straight thick line. Both custom boards are difficult to build, requiring some patience to get the tiny 0402 passives in place. I noticed that the Chinese board uses 0603 components, but the build area is also 50% larger than my custom boards.
I don't know if it makes sense for me to try to sell these since these custom boards will never be price competitive with the $3 imports. They are more for me to get used to using the Nordic technology in preparation for the next level; building an add-on board for the Nordic nRF51822 bluetooth LE chip.