Serial Console

From OpenTom

The Connectors at the bottom of the device contain an RS232 serial port at 3.3V level.

The port runs at 115200 bps 8N1. Hardware flow control isn't used so you only need to connect TxD and RxD.

You will need some small circuitry with a MAX3232(product page, datasheet) or similar in order to get the voltage to RS232 level.

Alternatively, the following RS232-powered circuit will also work (this circuit is only for output. If you also want to send data via RS232 to the TomTom, try the bi-directional level shifter):

It draws power from DTR. The 1N4148 protects against negative voltage. (Any similar diode is fine.) Instead of a 78L05, a 7805 may work. If using a different logic family than HCT for the 7404, please check that Voh (output high voltage) is close to 5V and that Vih (input high voltage) is well below 3.3V. Here is a comparison chart.

Be sure to connect all unused inputs to ground. Otherwise, they will pick up ambient noise and increase power consumption above what DTR can drive. This circuit can drive an RS232 cable of several meters (tested with 3m).

For an even simpler, but less reliable circuit, look at this Analog level shifter.

See also the entry about a different docking station using two docking stations to make a single one.