Analog level shifter

From OpenTom

This analog level shifter converts the 3.3V signal from the TomTom's serial port to something a PC can handle:

The values for R1 and R2 were found by trial and error. If you only get noise, try changing them. Do not make them much smaller than they already are !

D1 is optional, but if removing it, R1 or R2 may have to be adjusted. Almost any "generic" diode can be used for D1 and D2, and almost any "generic" NPN transistor for Q1.

This circuit produces a horribly ugly signal. You're better off with the one shown on the Serial Console page. The following comparison between the two level shifters illustrates this:

On the left, we have the digital one, on the right, the analog one. The input from the TomTom is shown at the bottom. The top shows the signal output into the PC, connected through a 3-4m cable.

The following pictures show both circuits. The Sub-D connectors are soldered to the PCBs, which yields a solid mechanical connection.