Gentlemen: Thanks for the explanation. The link and traces certainly made it clearer.
Jim
TomDiehl wrote: Stevert wrote: Soo Line fan wrote: I have never heard a good explanation of exactly what a DCC signal is. A lab scope trace would be nice to see. Jim Sorry, I missed this the first time around. Isambard gave you the good explanation, and the scope traces come courtesy of Allan Gartner's excellent DCC Web site. Note that this series of traces are in illustration of a specific DCC wiring problem and fix, so while the first image shows a "normal" trace, the others show various levels of distortion: http://www.wiringfordcc.com/dcc_waveforms.htmSteve Looking at the waveform in the link, the signal is a pulse train, almost impossible to read accurately with anything but an oscilloscope. Note that the positive and negative portions of the wave are not equal in duration (width on the scope screen). A true square wave can be measured somewhat accurately with a voltmeter, as long as you know you're dealing with a square wave and not a sine wave. The variation you see on the voltmeter can simply be the throttle setting depending on what the setting does to each pulse.
Stevert wrote: Soo Line fan wrote: I have never heard a good explanation of exactly what a DCC signal is. A lab scope trace would be nice to see. Jim Sorry, I missed this the first time around. Isambard gave you the good explanation, and the scope traces come courtesy of Allan Gartner's excellent DCC Web site. Note that this series of traces are in illustration of a specific DCC wiring problem and fix, so while the first image shows a "normal" trace, the others show various levels of distortion: http://www.wiringfordcc.com/dcc_waveforms.htmSteve
Soo Line fan wrote: I have never heard a good explanation of exactly what a DCC signal is. A lab scope trace would be nice to see. Jim
I have never heard a good explanation of exactly what a DCC signal is. A lab scope trace would be nice to see.
Looking at the waveform in the link, the signal is a pulse train, almost impossible to read accurately with anything but an oscilloscope. Note that the positive and negative portions of the wave are not equal in duration (width on the scope screen). A true square wave can be measured somewhat accurately with a voltmeter, as long as you know you're dealing with a square wave and not a sine wave. The variation you see on the voltmeter can simply be the throttle setting depending on what the setting does to each pulse.
In theory the high and low side of each "wave" are of equal duration, but the zeros are long, and the ones are short, so it is only a square wave during a stream of ones or zeros. If you are using address zero to run a DC loco the high or low side of the zero is stretched to change the average voltage from zero to a positive or negative voltage to drive the DC loco. I think from reading the spec that it would be allowable to have an average of other than zero, but then channel zero would not be available.
Jeff But it's a dry heat!
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As noted in other posts, the DCC signal, which acts both to provide power and commands, is essentially a series of square waves. The Digitrax Big Book of DCC describes the DCC signal as a bipolar square wave with the amplitude of the full track voltage. A binary "one" half cycle is between 52 and 64 microseconds duration and a binary "zero" half cycle is at least 90 microsecond in duration . The Digitrax Big Book (currently under revision) is a good source of information, including scope traces. MR's "DCC Made Easy" by Lionel Strang is also a useful reference.
Isambard
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Soo Line fan wrote:I am still using DC so I am hardly an expert but a couple things come to mind. Is your DMM a “true RMS” meter? I have 3 DMMs and only my Fluke 87 is an RMS meter. If not you may be getting an inaccurate reading. Jim
I am still using DC so I am hardly an expert but a couple things come to mind. Is your DMM a “true RMS” meter? I have 3 DMMs and only my Fluke 87 is an RMS meter. If not you may be getting an inaccurate reading.
For example: An automotive Hall effect switch measured with a DMM will read ½ of system voltage due to the 50% duty cycle. The meter averages the voltage signal. That is why many meters have a duty cycle setting on them; using voltage on a Hall effect is misleading.
One work around worth trying is to remove the shell and check the voltage after the decoder converts it. Then a standard DMM will be able to measure it. I have never heard a good explanation of exactly what a DCC signal is. A lab scope trace would be nice to see.
I have no information on the Zephyr, but most DCC units have settings for track voltage commensurate with the demands of the various scales. Your setting may be for N-scale, which you can verify by reading the instructions and looking for a switch and indicator.
Sorry that I can offer nothing more. Hopefully, it will be something as simple as setting the voltage for your scale.