The ~Process~
- Designing a bluetooth node The first part of this week's assignment was to design a new board. I started off with the hello.RN4871 from the website but made a simple modification. I added an LED and current-limiting resistor to be able to control from my laptop. Here is the design in Eagle:
- Cutting and stuffing Now off to clank. Now that we had been kicked off campus I had to retightened the belts of the clank that had been shipped to me. I had A LOT of trouble with this back in Cambridge, but was able to use pliers to get some grip and leverage. The belts should be tight enough that, when plucked, they give off a pitch similar to that of a guitar string. With this done I exported the PNG from eagle, put it through mods, and began cutting.
- Connecting wirelessly to the RN4871 Now with the PCB stuffed I connected it to my computer for power and followed a couple of tutorials to begin communicating with the chip. I used miniterm,arduino, and an app called Light Blue. The light blue app connects to bluetooth devices and can be used to read or write from those devices. When I used miniterm to ask for the name of the bluetooth device I ran into a strange issue: the output was completely unintelligible. I would only get a bunch of strange characters in response:
When cutting out the outline, I made the mistake of stopping the job then restarting the job without re-zeroing. The bit got stuck in the PF and got stuck. It was very sad. Luckily I had a couple more to spare.
Once cut out, I stuffed the board. I tried doing this doing the rework way, by adding solder to the pads, then putting the chip on top, then using the hot air to fuse the chip to the board. However, when I did this I added too much solder to the pads, and not evenly enough. This resulted in it taking more time for the solder to melt, and actually melted the diode (i think it's a diode anyways) off of the RN4871 chip. After briefly freaking out, I resoldered the blue component back onto the RN4871 chip, ensuring that it was aligned correctly.
I spent a few hours debugging then talked to Anthony. We tried a couple of different things: probing TX/RX, flashing the chip with firmware, and a few other things. Guess what? I didn't connect the RX on the Bluetooth module to the RX connector. Apparently whenever I made the net in the schematic in Eagle i messed it up so that it didn't show up in the board file. I soldered a wire to the RX pin on the Bluetooth module, but alas, to no avail. We also tried bypassing the regulator, which also didn't work.
I'm still working on a solution to this, and am going to try to cut out a new board. Unfortunately, only one chip came in our home lab kits so I'm going to have to wait until the new chip comes in.
Using the Lightblue app I was able to determine the name of my device: BLE-A2D4. Once I figured this out I connected to it using the app! Unfortunately, when I connected it didn't automatically give me options to read from the device. This was because I was using the wrong setting in the app, here is a screenshot of the two different times I connected:
