Why would TomTom remove the earphone plug? There are a few simple reasons, one being that the new version has a slimmer formfactor with less room for plugs, and the other being that they probably don’t want it to compete too much with the XL and Rider versions.
When my iPaq PDA died on me a few weeks ago, I was in desperate need of a new navigation system, and it already was clear that it had to be a TomTom, because I like the simple user interface and the clean look of the map and information when I’m driving. I also wanted to use it on my motorcycle, but wasn’t ready to shell out 600 euro’s for the occasional bike trip. Compared to the 600 euro’s I had financial room to screw up three 200 euro TomTom Ones :-), so I had a go at one, and here’s how it worked out.
First I opened it up and looked for a spot to place a 3.5mm earphone jack. There was (ver little) room at the bottom of the unit just behind the SD slot. An ordinary 3.5mm Jack wasn’t going to fit, so I canibalized my iPaq for a small 3.5mm connector. Some careful measurements later, I decided it would fit, and started the electrical investigation before drilling holes in the unit.
I cut the read wire to the internal speaker and tried a couple of resistors in series with my earphones to get the right audio level. With the earphone’s left and right speakers in series, a resistor of 470 Ohms sounded nice. Loud enough to be heard on a motorcycle, not so loud it would ruin my earbuds and -drums, and the volume slider controls the volume nicely. As you’ll see this is an unorthodox connection for earbuds, since the ground lead is not connected. It is a matter of choice, you can connect the earbuds in parallel if you like, the impedance only changes a few Ohms. Compared to the 470 Ohms resistor you will probably not notice the difference. I didn’t bother to change it.
In the 3.5mm plug from the iPaq there is a nice switch to disconnect the internal speaker. When I insert the earphones, the internal speaker is turned off, just like you’d expect.
With all planning and preparation done, it was now time to drill the hole in the TomTom case, the official point of no return. After the drilling, removing the battery and some fiddling with glue, the connector would not sit still while the glue was drying. I taped it to the base so the glue could settle. Be careful not to smear glue into the 3.5mm connector, the casing is not 100% closed because of it’s size. You can actually see the metal of the connector for the left earphone piece in the picture. Glue that and you have a useless connector.
After the glue dried, I reinstalled the battery with a fresh piece of double sided tape, and did the wiring properly. To prevent wires and the connector from hitting the copper shield of the circuit bord, I strategically placed some isolation tape on the bare soldering joints. After that, the TomTom could be cloded up.
As you can see on the right (click on it for larger image), the end result is pretty neat. As it turns out, the connector is not in a very different spot compared to the older model TomTom one. I tried it on my bike today, and it works nicely. I put the TomTom in a pocket of my jacket so I can not see or touch the display, but the spoken instructions are good enough compared to the money it cost me to do this (10 cents for the resistor, not counting the 3.5mm jack I got from my iPaq). You can hear the instructions while driving 120km/h on the freeway, unless you’ve got very loud pipes…
Now go and roll your own!