Weak DCS signals, Failed TIU Output Drivers, and Design Solutions devloped under collaboration between AGHR and MTH

I found someone with an oscilloscope who is going to let me test a TIU on it, and I have a couple of basic questions.

1) If my TIU is powered externally but not connected to a layout and no locomotives are present, what do I press on the remote to get the TIU to issue a bunch of signals that I can measure? 

2) Can I just connect the scope directly to the TIU outputs, or do I need the filter that GRJ mentioned in an earlier post.

johnf posted:

I found someone with an oscilloscope who is going to let me test a TIU on it, and I have a couple of basic questions.

1) If my TIU is powered externally but not connected to a layout and no locomotives are present, what do I press on the remote to get the TIU to issue a bunch of signals that I can measure? 

2) Can I just connect the scope directly to the TIU outputs, or do I need the filter that GRJ mentioned in an earlier post.

2 gotta have the filter or you won’t see anything and won’t be able to trigger at a set level with the 18V 60 Hz underneath

1 it sends packets anytime the TIU is reset or of there’s any transients on the track so it's easiest to just toggle power.

 

 

 

 

 

Ringy?  Please explain?  These are suppose to be square waves, but in all of the pictures that we have all shown, none of them are square.  Is the so call "square wave" suppose to look as we have shown them in the photos or is there a lot of distortion being introduced some where in the circuit?

Bob D

 

 

 

rad400 posted:

Ringy?  Please explain?  These are suppose to be square waves, but in all of the pictures that we have all shown, none of them are square.  Is the so call "square wave" suppose to look as we have shown them in the photos or is there a lot of distortion being introduced some where in the circuit?

Bob D

It's a square wave plus an e^(yt) x cos(wt) term from all the wire inductance like the last part of the tutorial talks about. The amplitude is fine and if johnf tightened up the loops in the wire it's be a square.

gunrunnerjohn posted:

I don't get all that square a wave when tapping right off the filter with no track or extra wire in place.  I wonder if a terminating resistor would help?

The downside is the terminator itself costs you  excursion voltage. The ringing shouldn’t matter much because the engine itself acts like a terminator and it’s always co-located with the decoder.

If it’s really bad it may be time to tighten up the split power-gnd sections of wiring. The split of + and - is what causes those rings 

Adrian! posted:
rad400 posted:

Ringy?  Please explain?  These are suppose to be square waves, but in all of the pictures that we have all shown, none of them are square.  Is the so call "square wave" suppose to look as we have shown them in the photos or is there a lot of distortion being introduced some where in the circuit?

Bob D

It's a square wave plus an e^(yt) x cos(wt) term from all the wire inductance like the last part of the tutorial talks about. The amplitude is fine and if johnf tightened up the loops in the wire it's be a square.

The part I am not following is the measurements that I have taken, have been straight off the output terminals of the TIU (no track wiring), where the impedance should be very low  (small R) resulting in minimal ringing.  But I still seem to be getting a lot of ringing?  What am I missing?  

Sorry for all the questions.  Thanks

DS1Z_QuickPrint1

 

 

 

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rad400 posted:
Adrian! posted:
rad400 posted:

Ringy?  Please explain?  These are suppose to be square waves, but in all of the pictures that we have all shown, none of them are square.  Is the so call "square wave" suppose to look as we have shown them in the photos or is there a lot of distortion being introduced some where in the circuit?

Bob D

It's a square wave plus an e^(yt) x cos(wt) term from all the wire inductance like the last part of the tutorial talks about. The amplitude is fine and if johnf tightened up the loops in the wire it's be a square.

The part I am not following is the measurements that I have taken, have been straight off the output terminals of the TIU (no track wiring), where the impedance should be very low  (small R) resulting in minimal ringing.  But I still seem to be getting a lot of ringing?  What am I missing?  

Sorry for all the questions.  Thanks

DS1Z_QuickPrint1

I think the discrepancy is some of us are using high speed scope probes (low L) and some of us aren’t. The TIU itself has a transformer at the output so it may ring if it’s not de-Q-Ed by the scope probe. I think this plot and the other one by Johnf are fine. Those overshoots won’t do much to the decoder since the one and zero levels are very clear 

Adrian! posted:
rad400 posted:
Adrian! posted:
rad400 posted:

Ringy?  Please explain?  These are suppose to be square waves, but in all of the pictures that we have all shown, none of them are square.  Is the so call "square wave" suppose to look as we have shown them in the photos or is there a lot of distortion being introduced some where in the circuit?

Bob D

It's a square wave plus an e^(yt) x cos(wt) term from all the wire inductance like the last part of the tutorial talks about. The amplitude is fine and if johnf tightened up the loops in the wire it's be a square.

The part I am not following is the measurements that I have taken, have been straight off the output terminals of the TIU (no track wiring), where the impedance should be very low  (small R) resulting in minimal ringing.  But I still seem to be getting a lot of ringing?  What am I missing?  

Sorry for all the questions.  Thanks

DS1Z_QuickPrint1

I think the discrepancy is some of us are using high speed scope probes (low L) and some of us aren’t. The TIU itself has a transformer at the output so it may ring if it’s not de-Q-Ed by the scope probe. I think this plot and the other one by Johnf are fine. Those overshoots won’t do much to the decoder since the one and zero levels are very clear 

Adrain thanks.  I am trying to address the DCS issues at the club and wanted to make sure that I am dealing with TIUs which are generating a good signal before address layout issues.

 

 

 

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