Transistor logic probe

This is a simple logic probe based around a transistor

A Logic low will switch the LED off

A logic high will switch the LED on

Schematic

transistor logic probe

Parts List

QTY  PART-REFS           VALUE                                 
---  ---------           -----                         
Resistors
---------
1    R1                  10k                                               
1    R2                  1k                                                

Transistors
-----------
1    Q1                  PN2222                                            

Diodes
------
1    D1                  LED