Tutorial: Adding Active GPS to the Moverio BT-200

2015-05-26 17.28.39 2.jpgThe Epson Moverio BT-200 is a great heads-up display attached to a shit computer. Here’s how to replace its worthless chip GPS antenna with a high-powered active receiver.

Some fun facts about the Moverio BT-200’s location awareness:

  • It doesn’t get your location from Wi-Fi or a tethered phone because Epson was too cheap to license Google Play Services.
  • It relies wholly on a crappy chip antenna that can barely detect a single satellite.

This mod replaces the crap bipolar SMD chip antenna with an amplifying active receiver that can magnetically attach to your shoulder.2015-05-26 16.36.57 2 copy.jpg

IMPORTANT: DO NOT JUST COPY THIS PICTURE. This was a test. Copying it will add too much interference to the GPS signal.

Step 1: Materials

  • A Moverio BT-200
  • A 3.3V active GPS antenna. I’m using the Trimble 66800-52 D.
  • A uFl-SMA bulkhead jack, as short as you can find. Mine is 2″ and came from an XBee devkit.
  • 28-gauge or so magnet wire
  • A standard SMD uFl jack. I salvaged mine from a burned-out XBee.
  • A strong magnet or piece of steel, for mounting the antenna
  • Standard SMD rework equipment

Step 2: Move the frontend

  1. Open up your BT-200. Release the trackpad and buttons. Remove the RF shield. Remove the PCB. Unclip the battery.
  2. Desolder and discard C82, C121, and R266.
  3. Desolder C122 and solder it in R265’s unpopulated pads.
  4. Bridge the leftmost pad of R266 with the leftmost pad of R265

The resistor is redundant, as the Jorin WG76XX RF chipset already has 50Ω impedance-matching resistors onboard. We’re replacing the resistor with a cap so we can power our antenna directly off the 3.3V rail and draw more than the 10mA or so the WG76XX can provide.

Step 3: Solder down the uFl socket.

  • Solder the uFl socket onto the unpopulated CN8 pad.
  • Why did they put uFl footprints on the board but use crappy chip antennas?

Step 4: Add power

  • Cut a few inches of magnet wire and strip one end.
  • Wrap it six times around a 3/32 drill bit to add a coil.
  • Solder one end to the bottom pin of CN6, which connects to the 3.3V rail.
  • Solder the other end to the center pad of CN8, where the trace connects to the socket.

Active antennas have an actual amplifier inside the case that’s powered by ‘phantom power’. Because the GPS signal is wholly AC and the power is all DC, they can both be sent through the same wire and separated later. The capacitor you placed in R265 ensures that the GPS chipset only gets the AC, and the coiled wire rejects high-frequency supply-line noise from the 3.3V rail that could contaminate the signal.

Step 5: Add the jack

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  • Use a Dremel or band saw to cut a relief into the PCB. Start just above the top-left mounting hole and continue to the ground plane to the left of AT2.
  • Sand the cut smooth so it doesn’t slice through the jack’s insulation.
  • Drill a 1/4″ hole centered vertically on the top of the case, aligned with the notch.
  • Mount your jack and snap the uFl connector into place.

Here’s another pic of the mounted jack for reference:

2015-05-26 17.21.57.jpgStep 6: Finish the job

  • Snap the battery jack into place. Screw in your active antenna. Manually actuate the switch and verify that the GPS functions.
  • Reassemble the BT-200.

Job’s done!

Slip a strong magnet or a chunk of metal under your shirt or backpack, and snap your antenna to it so it faces the sky. Instead of struggling to find one satellite, your BT-200 should now easily snap onto six or eight, with up to 12 channels on a clear day.

Note for fearmongers: GPS is receive-only. GPS signals are transmitted by satellites orbiting the globe. No radio waves are leaving the GPS antenna – it’s only listening harder to the waves already hitting the wearer. There is no conceivable line of attack to argue that this mod could affect the user’s health.

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