While tinkering with my unit I found an easy and quick way to add a microphone to this deaf unit. With a microphone, you will be able to take advantage of voice recognition for navigation. It will involve a small amount of soldering but almost anyone will be able to do this. What you will need:
Small phillips head screwdriver
Soldering iron and solder
Small microphone (I salvaged mine from an old headset)
A small drill.
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Step 1: Take the Back Cover Off and Locate the Solder Point.
The back cover has four screws. Remove those, and disconnect the battery and speaker from the main board. Set aside the back cover. On the main board, locate the area underneath the gps receiver and to the left of the sd card slot marked "mic1", and take note of the two traces with solder on them directly to the left of "mic1". There may be a sticker there that you have to peel off.
Step 2: Get Your Microphone Ready and Drill Some Holes.
Get yourself a microphone. Find a good location to mount it. Mine was sized perfectly to fit next to the gps receiver in the case. If I had a smaller one, I might have made it point to the front of the unit, but I had to point mine up. I'd advise against pointing it towards the rear for obvious reasons. Wherever you decide to place yours, drill a hole into the case over the location of your microphone so that it can hear you.
Step 3: Mount and Solder Your Microphone.
You should have already cut your wires to length. Run the wires carefully to the "mic1" area and solder them to the two traces. Place your microphone in its new home and glue it in place. Try not to get glue on the microphone head.
Step 4: Close Her Up and Turn Her On.
Reconnect your battery and your speakers and close up the back of your unit. Go to the Navigon store down the street and buy your software and maps. Put in your SD card. Turn on your unit and run Navigon. Press voice entry on the main menu, and you should be able to complete the training. You must have the Phoneme.nsf file that corresponds to your map version, otherwise "voice entry" will be replaced with "my maps". If you have problems with the unit not hearing you, check your soldering. Make you sure you don't have a loose or crossed connection. When I first tried the voice training, it said I spoke too loudly. That made me realize it was actually working. Also, you don't have to use Navigon. Use whatever software you want. The point is that you now have an on board microphone. Enjoy!
(The only map version of Navigon that works with voice recognition in the US is 2008 Q3. You must have that map and the corresponding phoneme.nfs file.)
Note: Ignore the red and white wires I have hanging out next to the gps receiver in the photos. That's for an automatic power on mod that will be coming soon.