Switch question without voltage drop

I have attached an image.

I have 2 voltage sources coming in the circuit (X and Y). If voltage is present on X, then Y is not needed. X takes priority in this circuit, so Y is only used if no voltage is present at X.

Currently, I am using a mechanical switch as in the top diagram. I want to get away from this; however, I need 5v at Z whether using X or Y.

If I use a transistor, such as a PNP, in the lower diagram, which would tell me if X is off, then I would have to use a Diode on X to prevent the voltage from Y altering the state of the transistor. When I add the diode, I will get a minimum of a .6 voltage drop which I cannot have. I must have 5 volts at Z.

I'm looking for solutions.


Thanks!


**broken link removed**

There's far too little information there, you need to provide EXACTLY what everything is, and how it's connected.

Hopefully this will help a bit:

I'm using a PIC 16F88 to read voltages from an automotive sensor. The "Load" would be the ADC input (PORTA,4). I have a 1k resistor before the ADC port to reduce the current.

I haven't calculated the "base" resistor for the PNP transistor, but it shouldn't take much current to saturate the transistor.

It seems the easiest thing to do is to run one more ADC channel on the PIC. It has 7 ADC inputs.

Then just use software to decide which reading to use.

Diver300 said:

It seems the easiest thing to do is to run one more ADC channel on the PIC. It has 7 ADC inputs.

Click to expand...

Yes, by FAR the best way - particularly as he must have a spare pin as he's using to switch inputs.

ALright guys, I'll think through what you've given me and work up a plan.

Thanks!

superflux said:

ALright guys, I'll think through what you've given me and work up a plan.

Click to expand...

What's to work out?, everything you need is already in the chip - check my PIC tutorial which uses two channels of the A2D.