USB to RF Transceiver prototype complete!
This is just a post to point you over to my new Transceiver page. I took the work that I did on the MRF49XA transceiver, and added an Atmel AVR USB micro controller. I prototyped is using the AT90USBKey development kit, and designed a custom PCB that includes the transceiver and an AT90USB162.
I wanted to design the board such that all the “guts” were on the “back” side of the PCB. The photo above shows the transceiver circuit (surrounded by a strip of track that you can use to solder a “fence” or “can” to manage RF interference), and the AT90USB162 micro controller. This can be replaced by and 2 series USB micro controller, like the ATMega32U2 or the AT90USB82. I recommend using the ATMeta32U2, though the first run of boards have the AT90USB162. I’ve also included a dedicated 3.3v voltage regulator, because the built-in regulator inside the AVR doesn’t have a clearly marked current capacity, and I didn’t want to risk it. I’ve also included every spare pin from the AVR that was practical.
The other side of the board contains all the user facing parts. This includes the status LEDs, the SMA connector, USB port, and the boot loader and reset buttons. My grand idea here was that I could mount a piece of plastic to the component side to protect them, while having access to all the bits I need to use. In hindsight, this means that it’s a “double-sided load” which is harder to manufacture. I ended up having to learn a new technique to solder the USB port. Notice that the can of the USB port covers the pads? It’s very difficult to solder those on. It helps to “tin” the pads first, then set the USB port on top of them. Luckily, the USB port has little plastic pins that keep it aligned. When you’re pressing down on it, just hit it edges of the pads with the soldering iron, and it should solder just fine. When that’s finished, solder the mounting tabs on the sides.
Also, the buttons I bought aren’t “process compatible” which means that you can’t wash the board with them installed. To deal with this, I reflow solder the entire board, then put them in my new ultrasonic jewelry cleaner with time isopropyl alcohol and brush them with a toothbrush, finally rinse off the alcohol and dry with compressed air. Once the board is cleaned, then I solder on the buttons.
Lessons (mostly) learned? Think about how you would assemble something when you’re designing it!! Building the board this way adds 15-20 minutes of assemble time. Bummer.
Also, here is are the gerber and eagle design files: Design files.
Work on the software is ongoing. Click on the transceiver’s main page (link at the top) for updates. Enjoy!