Given that I have a 3 pin SPDT switch in ON-OFF-OFF configuration, (common pin, switch1, switch2), 5v and gnd is there a simple circuit using discrete components that would give me a 0v if switch 1 is set, 2.5v if off and 5v if switch 2 is set?

It seems overkill to use a small PIC microcontroller to rear the state of the switch and drive several transistors to generate the required voltage using resistor network.

 

Why pick The OFF position for power?
You can not use SW1 & SW2 with centre OFF (0v)?

 

Yes, just put two equal-value resistors between common and switch1 and between common and switch 2.

 

Where is 2.5V coming from? If you have regulated +5 but no regulated 2.5V, I'd use an LM317 voltage regulator to make the 2.5 volts, depending on the current needed.

If you need any significant current at 2.5V (if you're actually trying to supply power to something), the voltage divider that lan0 is eluding to above won't work.

 

There is a bit missing as all of the 3 pin, 3 position switches that I am familiar with are center off.
Really, the question does not make much sense to me.

 

all of the 3 pin, 3 position switches that I am familiar with are center off.

Nope, off/on/on switches do exist. I had to buy one to replace a toggle switch on a spectrum analyzer.

 

Sorry, I got the original post wrong. It’s a on-off-on switch with middle position off. The output from the circuit is feeding an Ecu input which requires 2.5v if no switch is selected, 0v if one switch selected, and 5v if other switch is selected. There is a regulated 5v output from the Ecu which is available along with sensor ground

 

Since the 2.5 v is only used as a signal, a voltage divider would work. Two 5k resistors would work well.

Can't draw a sketch at the moment.....

 

I’ve done a simple circuit which was based on two separate switches, but not the SPDT 3 pin switch, which I have to keep as it’s part of an existing assembly.

 

 

That’s a perfect solution and very compact