Week Thirteen: Networking and Communications

radio to nowhere :(

Task

Build a wired and/or wireless network with at least two nodes.

Tools

Result

This week I wanted to make hello_radio as a wireless communication starting point for my final project. The ballroom dance partner peace mediating system will work much better if people aren't tripping over wires all the time; and hello_radio is the starting point for some other projects in my research group.

I ended up with two boards with unresolved(able) issues. Typically this started as bridges off the radio or ATMega and ended up as torn traces post-"repair" process. My final version "should" have worked--there were no bridges, ripped traces, and the board was not overheating. But it still wouldn't program so I must have been overlooking something.

Files

The code, board and parts files can be found here.

Approach

I used the hello_radio image files to mill three boards (two plus a back-up) on the Modela. The power outage disrupted my plans to get an early start this week before leaving town for the weekend. Despite the delay, milling went fairly smoothly though I was concerned that the through-holes in the cut file didn't show up in the make-path image at the recommended 0.79 mm diameter settings. They did show up at lower diameter values, and cut through regardless of whether they appeared or not. Possibly my eyesight just wasn't up to the task of seeing them.

The bill of materials helped me gather the components for the board---it was a fairly lengthy list! I was glad to have Dan Novy's taping and labeling trick up my sleeve. I then started stuffing the board from inside out, low to high. This took close to an order of magnitude longer than past weeks. I found it difficult to line up all the feet on the ATMega 168 and the MRF498A and I also had many issues with bridging. It's a lot of parts in not a lot of space. Some of the traces peeled off and the legs bent because of overheating during the many times I removed and reflowed solder. I successfully reconnected a few by patching in some wire or solder braid but always managed to mess up something else in the process. The wire-cutter microscope in E15-043 was really useful for identifying issues--thanks to Dan Novy for help with this too!

I used small pieces of wire (normal resistor legs) to attach the bottom on top of the board via the through holes. I soldered one strand of the ribbon cable to the center pad of the antenna and used the copper braid to attach the top and bottom along the left hand side of the board off the two pads outside the antenna.

After stuffing the board, I programed it using the hello.radio makefile. Make sure to download hal_hello_radio-016.h as well. Unfortunately I was unable to successfully program any of my boards...even though the last one looked so promising. This will continue to haunt me for weeks.

Trials and Tribulations

This week was a whole new level of soldering--those parts are small and plentiful. It took me a lot longer to stuff the board than in past weeks. It also took many steps of debugging and I had quite a few issues with traces ripping off due to overheating.

Fortunately, I milled a back-up board and managed to cleanly solder the radio and the ATMega (thanks Dan Novy for double checking this for me!). The rest of the soldering went smoothly as well, but the board still wouldn't program. This board did not become hot like the others did, so I don't think it was a short. I'm not sure what the issue is though....the resonator was soldered slightly crooked, but mild clean-up and retouching didn't change anything. It got late enough that I became careless and decided it was better to quit and get a second opinion before I messed things up further.

Links