My old ocilloscope hasn't the bandwidth to properly display my DCC signals. Does anyone on the forum have any suggestions as to what would be a good scope for this? I am thinking of a digital storage scope but what bandwith would be enough?
73
Bruce in the Peg
I'm more than a little surprised. DCC is slow in o-scope terms, even if it's a really old scope. What do you have?
Jeff But it's a dry heat!
That is On Topic as far as I am concerned.
A digital storage scope is far more than you need unless you have money to spend.
I have a solid state Velleman HPS5 which displays my NCE Power Cab waveforms very well.
* Max Sampling rate 5 MHz for repetitive signals (0.5MHz for single shot events) * Input Amp Bandwidth: 1 MHz (-3dB@1V/div setting) 1Mohm/20 pf * Max input voltage 100V peak (AC + DC) * Vert Resolution: 8 Bit (6 Bit on LCD) * LCD Graphics: 64 x 128 Pix * dBm: from -73dB to 40dB (up to 60dB with x10 Probe) * True RMS Measurement: AC .1mV ~ 80V (upto 400Vrms with x10 Probe) * Time Base: 20s ~ 2 us / div in 22 Steps * Input Sensitivity: 5 mV ~ 20V/div in 12 steps (up to 200V/div with x10 Probe) * Supply voltage 9VDC
* Battery (5 x AA) or adapter operation.
You can see the ringing in the waveforms as I had not yet put a termination on the buss wires.
There are newer models out as mine is about eight years old. I paid about $150.00 for this scope back then.
There are quite a few PC scopes and standalone solid state scopes for sale. You just have to know what you are looking for.
What is the make and model of your scope?
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
I will add one more photo. This is the decoder signal on the orange and gray wires connected to the motor terminals. The throttle is at half speed forward, direction.
Even most old tube-based scopes could do 5Mhz. It was the expensive ones you needed (and they still are relatively expensive) for over 100MHz. A 5MHz scope should be MORE than plenty for DCC.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
As Rich has shown, what is true is that without a storage scope it is going to be hard to really see the signal other than the magnitude, since if there are any data packets being transmitted, you won't get triggering at the same point in the waveform every time.
While a scope to see the waveform is fun, it certainly isn't much needed unless you are trying to do some "home cooking". A meter will tell you that you have voltage, and give you clues if something is "stuck". I can't really imagine many control system failure modes that would make a scope needed.
All of that said, I would enjoy having a scope just for fun!
There's that, too. I've always wanted a scope, but then it comes down to "but what would I DO with it?" it would be fun to check the waverforms, at least for a little while - but then what? Basically an expensive toy. What little I do do, is mostly digital in nature and a scope wouldn't help much. Analog devices are usually slow responding and have a threshold to do something, like a phototransistor switching on a relay - that I can monitor with a DVM. I wouldn;t turn one down if it was available for cheap but to go buy a new scope - nope, I'd rather buy trains. Definitely NOT a required tool to build a DCC layout.
Sorry for being so long to reply. My scope is a 1965 Telequipment (English Tektronix) model S54. It speced out at 10 mHz vertical and 1 mHz horizontal but that was when it was new. I no longer have access to the equipment necessary to calibrate or even verify these specs.
I have been building various electronic projects for many years and that is how I obtained a Tek 475 and the Velleman. The Velleman is digital, just not a storage type Scope. You might say, a digital/analog Scope. In short, no tubes in the Scope, only transistors and Integrated circuits. Some have thought digital Scopes were storage Scopes.
It was useful in check the waveform on the layout to see if we should have an RC termination at the end of the buss.
Some do have DCC issues, usually on large layouts if there is quite a lot of ringing.
For many, this is not an issue.
When I was a machine mechanic, I used a digital Scope to trouble shoot solid sate machine drives and the Scope could pick out a mis-firing SCR but storage capability is needed for that purpose.
If really interested in the pulse train, get a DCC NCE packet analyzer.
Blind Bruce Sorry for being so long to reply. My scope is a 1965 Telequipment (English Tektronix) model S54. It speced out at 10 mHz vertical and 1 mHz horizontal but that was when it was new. I no longer have access to the equipment necessary to calibrate or even verify these specs.
That should display the waveform OK. Definitely vacuum tube and that might be the issue if not displaying the waveform correctly. Some components may have changed value over time.
An inexpensive function generator will let you know how the Scope performs. I have one that goes from 10 Hz to 20Mhz, sine, square and triangular wave forms. For my use, this is just fine.
I verify the frequency using a frequency counter. And even those are not expensive anymore. Just don't do rocket science projects. I use to be a NASA contractor so I know the difference.
Again, I have been doing electronics projects as a hobby for many years.
I can tell you this from personal experience:
As our club has just completed our conversion from DC to DCC, a digital O scope would have been nice.
We were using a RR Ramp which is quite handy in determining if you have proper signal. But every once in a while a DC signal would get crossed with a DCC one and the RR ramp would go haywire. Having an Oscilloscope to determine which leg was corrupt would have been handy.
I figured out how to get around this by connecting one leg of the RR Ramp to a known good rail output on a seperate booster. The other leg went to the miswired section. If the RR Ramp was still haywire then I knew it was the current connected rail in the miswired section. If it read normal DCC then I knew it was the other rail in the miswired section.
There's also DCC packet inspectors available which spit out the commands that are being transmitted on the bus.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
A packet inspector would be much more useful than a scope.
I don't think there is any doubt that the scope you have has the bandwidth you need. But without a storage scope, it's going to be hard to actually see anything other than the presence of signal.
If you have the money to think about a scope, I think it would be much better to spend it on going to wireless throttle (if you don't already have them) or more locos! Unless you have other reasons to want the scope.
If I'm reading that scale on the second pic right you're only talking about 40khz.
Looks like it says 20us/div
Springfield PA
Hamltnblue If I'm reading that scale on the second pic right you're only talking about 40khz. Looks like it says 20us/div
Exactly.
The speed/bandwidth of the scope isn't the issue. DCC is very slow.
But if there is any data actually being transmitted, triggering with an analog scope, no matter how fast it is, is not going to be useful.
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