Some open board decoders provide a power supply negative
contact point on the board.
DCC Detector
The green boxes in figure 3 represent the circuitry that handles
the DCC data inside the decoder.
The DCC Detector looks at the DCC pulses on the track and
translates their timing into a stream of data pulses for the
“brains” of the decoder to use. The next few paragraphs and
figures will explain how different detector schemes work. If you
don’t care, jump ahead a couple of pages to the next section,
about the microprocessor.
The NMRA standards are that pulses that are nominally 55 micro-
seconds (µS) apart represent a data one. Zeros are indicated by
pulses more than 110 µS apart. So, to identify the pulses, the
detector needs to decide when a transition has occurred.
The most common method is to set a threshold (say 6 volts) and
presume that when the voltage goes above or below that level, a
transition has occurred. The disadvantage of this method is that
dirt on the track and other discontinuities may drop the DCC
signal level enough that transitions are missed. If that happens,
instead of a group of ones and zeros, the detector decides that
there was a long zero. Remember, zeroes are deemed to be any-
thing longer than 110 µS without a transition (5).
About 10 years ago, Lenz released their Gold series decod-
ers that used a differentiator to determine when a transition
occurred. In English, this means that, instead of looking at the
level of the DCC signal, the detector looks at the fact that there
is a change (difference) of voltage. Running the DCC signal (5)
through a capacitor creates the signal in figure 6. So why bother?
