Oscilloscope testing module (huntron circuit)
I call this the "huntron circuit" because a company
by that name made a similar device. It is useful for
trouble-shooting. I used it with digital PC boards where I did not
have a schematic, or even know how it worked. I recorded the
patterns found on a good board and compared them with the patterns
from a defective board. Any low power 12 volt transformer will
work, the resistors are ¼ watt.