> It's very simple. The center pin of each switch is connected to an

ADC pin

> of the microcontroller. In the center position the voltage generated

by the

> switch is ~ 2.5V (nothing but a voltage divider made with two resistors
> connected to +5V and GND). In the left/right position the terminal is
> connected to +5V or GND. If you apply a voltage in the range 0...+5V

to the

> center pin of a switch (and make sure that the switch is in the center
> position) you can switch between the 3 function with an external

voltage.

> But you have to pay attention that no negative voltage and no

voltage beyond

> +5V is applied. In this case the microcontroller will be damaged.

Protection

> diodes connected to GND and +5V in combination with a serial

resistor (~1k)

> should be sufficient.

am i right to assume that a diode has no value that needs to be
correct - any old diode from conrad will do

thanks, stu