The TC-4 is identical in function to the CIRCUITRON TC-2 above, except that the output of the TC-4 is designed to drive the CIRCUITRON TORTOISE? Switch Machine. The TC-4 can also be used with Switchmaster? and other brands of stall-motor switch machines that use the Hankscraft? display motor. The TC-3 requires a 12 - 18 volt DC input and is constructed on a 1?? x 3? printed circuit board.