Hardware

 

The first batch of PCBs has arrived!  I’ve only ordered three for the first batch, to make sure everything works as intended.  If they’re fine, I’ll order a larger batch the next time around.  Here’s what the board layout looks like:





You may also want to download the schematic (PDF), the board layout (PDF), and/or the Eagle file package (ZIP); all are available at the links in this paragraph.  The EAGLE file package is more up-to-date than the PDFs, but I haven’t yet tested the revisions it contains.  If you’d like to have your own boards made, you can also download the Gerber files I used and have them made at the fab of your choice.

On the prototype PCBs, the system is working well.  The clock and serial converter are functioning without problems, and the Teensy is working well also.  The DC-DC converter portion of the layout, however, isn’t working.  The pin pitch of the part is very fine, and I suspect that’s at least part of the problem.  I’m looking for another part now to solve that problem.  The unit works perfectly when plugged into a USB power source (which, as it happens, I already have in my plane), but not when powered from two AA batteries, which was one of my original goals.

On the breadboard, the hardware has been completely modular.  Right now, it consists of:

  1. •A Teensy 2.0 w/ pins microcontroller

  2. •An SD adapter, to allow writing to a micro SD card for storage

  3. •A DS1307-based Real-Time Clock module, which is needed in order to do the calculations on the data timestamps

  4. •A MAX232 module, which changes the voltage of the incoming signal to a level the Teensy can accept

  5. •An I2C 16 x 2 character LCD (this link is to the item I bought on eBay; the manufacturer/vendor’s page is here)

  6. •A Null Modem adapter

  7. •Various hookup wire to connect the modules

The latter five items were purchased from eBay.  I’ve given links to the items I bought, but other equivalents will work.

Looking forward, I plan to have PCBs made, and will abandon some of the pre-built modules.  I will be using the DS3231 Real-Time Clock instead of the DS1307 for two reasons: (1) the DS3231 is considerably more accurate, and resetting the clock is a bit of a hassle; and (2) the DS3231 requires no support circuitry other than a battery.  The interface to the Teensy should be identical, and no code changes should be required.