Designing a Circuit to Detect PNP and NPN Sensors

[DSelfridge]

Homework Statement

Workinfg on a project for a teacher currently and need help designing the circuit for how to detect whether a sensor is PNP or NPN. I need to have 2 9V batteries power the NPN or PNP sensor and then have a spot for the third wire, where if it is positive output (PNP) (sourcing) then one LED lights up, whereas if it is negative output (NPN) (sinking), then a different LED lights up. Any help?

 

[mfb]

Try to make a circuit with one LED first, I think the second one should be easy to add with an additional (known) transistor afterwards.

 

[DSelfridge]

Well I understand that but I only want to have 3 wire inputs for the sensor which then has both LED's tied to the same spot just each turns on depending on whether it gains a sourcing or sinking output from the sensor? does that make sense? I don't really know what to do for that, a bipolar transistor?

 

[mfb]

Just 3 connections for the LEDs? That's still possible.
Try to convert "pnp<->npn" to "low potential<->high potential" (somewhere) first.
Just 3 connections are easy if both LEDs can share a common connection to the power source (positive or negative side).