Many here will be familiar with the great little portable TIU port tester that Adrian did the basic design for, many contributed good ideas, and finally grj did the board design for. It was developed in a topic called $10-20 DCS-TIU Port Tester Tool; and it is being distributed by rtr12, and it works quite well. Thanks to Adrian, Stan, grj, and others, and rtr12 for doing all the heavy lifting to make this kit available!

When I reread the thread recently I was reminded that someone had suggested early on adding an LED to the output of each TIU channel to give a visual indication of DCS output. This would function like the red LED on Legacy and TMCC bases, which is a very handy tool for troubleshooting.

I figured what if a simple 2 port led board could be easily morphed from the basic kit design, and could be designed to mount neatly inside the TIU case, with just the indicator LEDs sticking out through the cover, one near each TIU channel output? A 2 port device would be useful if you are only using the two fixed DCS outputs say. If instead you are using all 4 TIU outputs, you could install 2 modules and cover them all.

There would only be two internal connections needed per channel, connected to the respective port terminal posts inside the TIU. Output channel power would be adequate to power the board, just like with the tester kit.

 I think many DCS users out there would be interested in such a device; it sure has appeal to me. It would be nice to make it through-hole design, like the portable tester, so anyone can build it. With any luck we can keep the costs down to about the same as the portable tester kit.

I am thinking only a single led would be needed per channel and the threshold signal level might want to be set at about 7-8 volts or so. That way any TIU kicking out the normal 10-12 volts or more will show an LED hit with every data packet. Ports with an output much less than 8 volts won’t activate the LED at all. If you are monitoring all 4 ports of your TIU, and suddenly one is not indicating when the rest are, you immediately know you have a problem. Sensitivity adjustment would be via a separate trim pot for each channel. So threshold voltage can be user set to whatever you like.

The portable tester uses 2 channels of a CD74HCT123E chip; one for the red led and the second for the green led. But we can use these same two channels for two separate TIU ports instead. 

I have poked around inside a Rev I3 TIU and it looks like there is space for two 22 x 76 mm pcbs along the inside edge, end to end, near the output ports. If using only one, it would straddle the two center fixed outputs. If using two, each would straddle one variable and one fixed output, mounted end to end.

The pairs of TIU output posts are spaced about 56 mm C-C apart, so the two leds (one per channel), would be about 10 mm from the short ends of the pcb, and very near the edge closest to the outputs. If the leds are close mounted to the board, they can be glued into their holes in the TIU cover, to provide mounting for the board.  A few details need to be worked out yet, but it looks doable. 

The module includes a 3 pin Dupont type header to allow selecting either TIU channel for module power. This would allow versatility of hookup regardless of how many, and which, TIU channels are being used.

Here is the circuit I came up with:

TIU Two Port Signal Indicator

To save some board space I deleted 2 stages of the original RC filter network, because I noted when testing mine with a scope there was no difference in output signal after 2, 3 or 4 stages. I have tested this with the portable tester and it behaves exactly the same as with all 4 stages. I kept the original blue power indicator led circuit just because it's handy to have.

I have landed on a preliminary board layout, which needs a few tweaks before I order some test boards.

So that's where I am with this project. I just wanted to test balloon this to forum members to see what level of interest there is, and collect any suggestions and comments you folks may have.  It's probable that I will soon go ahead and order up a batch of prototype boards, just to try the whole thing out.

Cheers, Rod

We are never too old to learn something stupid....

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First off, I'd suggest that the signal threshold will be variable, it will be based on the load on that channel of the TIU.  The simple DCS signal tester works because it tests the channel with no other connection to the channel, so the DCS signal is totally unloaded.  Given the variable loads presented by different layout configurations, I'm guessing you'll have results all over the map.  Truthfully, for one that was going to be active with the layout connected, I'd want more signal strength LED's, not less.

Next, the DCS signal tester only functions properly with a pure sine wave on the input of the transformer.  With electronic transformers, even at full throttle, the indications are frequently erroneous.  Removing some of the filter stages will only make it even more sensitive to the input waveform.  When I try to use the signal tester with my bench Z-1000 at full throttle, I still get erroneous indications, I have to jump in with my old 1033 to get proper readings.

Finally, if I were going to make something like this, I'd probably consider a device that didn't require calibration.  The reason that the HCT123 design requires calibration is the tolerance of the triggering voltage level for the chip.  I'd be looking at a design that didn't need calibration.

Aren't you sorry you asked?

Try using the simple test device with just a lighted bulb from a test track with the test device attached to track.  Totally different output from only the TIU output terminal.

What is wrong with the simple DCS track signal test if you think you have a problem, followed up with a TIU test?  KISS applies in my opinion.  G

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I recall a thread a while back about someone observing you can hear DCS activity on an AM radio?  Do they even sell pocket AM radios any more?!

Anyway, the idea might be to place the radio on the track section or loop in question and listen for activity.  I don't know what it would sound like but I'd think you'd hear "bursts" of static?  Obviously there are loose ends to resolve such as interference from other active DCS channels and what not...

Stan, I don't see how that would quantify the signal levels.  The Rev. L is rather prone to having only one or two outputs of the ACT244 fail and just reduce the DCS signal amplitude.  That being the case, it's important to actually check if a full amplitude signal is coming out for your tests.

I use my little tester for every TIU that comes in as a quick test.  If I see anything abnormal, I connect the 'scope and see if the signal is full strength.  I'm not sure how this tester would give me that assurance.

Depends on purpose of the tool.  If it's a "signal indicator" as Rod proposed, then I interpret that as sort of basic dead or alive indicator.  I think in many instances when there is a PS2 or PS3 command problem such as engine-not-found, out-of-range, etc. -  the user just wants to know if the DCS signal itself is present at all at ANY level.  

I agree that it's nice to get some quantitative indicator of signal strength.  However, that's why the original port tester tool "requires" an un-connected TIU output so that it's a known environment or load on the DCS signal generator.  As soon as you attach the DCS output to a track then all bets are off.  Are there engines on the track?  Are there TVS clamps on the track?  Lighted lock-ons?  Are you in passive mode?  What about lighted passenger cars without the DCS choke installed?  Lionel engines modified or not with a choke?  Small oval or gigantic club layout?  Etc. Etc.  I think Adrian in one of his earlier threads pondered, then abandoned, a method of measuring the "RMS" level of the DCS spread spectrum signal.  This is of course very difficult to do in a $10 widget.  So, instead, simple peak detection is used as a proxy of signal level.  As you may recall from the scope photos of the DCS signal, the peak detector is a marginal indication of signal level since you're looking at the ringing-overshoot of a complex digital RF signal.  The ringing is a function of the impedance of the track and its loads which as stated above is all over the map.  Anyway, lots of techno-babble and to what end.

In my opinion, what would be interesting is something like those pocket-size AC detectors that cost only a few bucks used to detect presence of a live circuit in your house.  No electrical contact required.  You place the widget near a wire and it gets brighter as you get closer to a wire with 120V AC on it.

 

Stan, given the sensor's requirement for a pure AC waveform to properly sense any level of the DCS signal, I'm still wondering how useful this would be.  Of course, this is just one man's opinion, I just don't know if it will actually serve the purpose with any consistency.  With anything but a pure sine wave in, the DCS tester says there's a good signal there all the time, even just connected to the transformer!  Any spikes on the output get through the filter.

Both of the transformers below give me a continuous "good" indication with the DCS tester connected directly and at full throttle.  The sharp slope obviously gets through the filter and triggers the detection.  Almost all the electronically controlled transformers have a similar waveform with the exception of the Z-4000 which synthesizes a sine wave.  That being the case, a ton of layouts would not be able to use this kind of detection.  Since the Z-4000 is buried right now, I haven't actually tried it connected directly to the DCS tester to see if it's "almost sinewave" is good enough not to trigger the detection.  Don't know if those little "squiggles" in the waveform would sneak through the filter.

Z-1000 full throttle waveform

mceclip1

CW-80 full throttle waveform

mceclip0

The Z-4000 was not tested as I don't have it unpacked at the present time.

Z-4000 full throttle waveform

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gunrunnerjohn posted:

First off, I'd suggest that the signal threshold will be variable, it will be based on the load on that channel of the TIU.  The simple DCS signal tester works because it tests the channel with no other connection to the channel, so the DCS signal is totally unloaded.  Given the variable loads presented by different layout configurations, I'm guessing you'll have results all over the map.  Truthfully, for one that was going to be active with the layout connected, I'd want more signal strength LED's, not less.

Next, the DCS signal tester only functions properly with a pure sine wave on the input of the transformer.  With electronic transformers, even at full throttle, the indications are frequently erroneous.  Removing some of the filter stages will only make it even more sensitive to the input waveform.  When I try to use the signal tester with my bench Z-1000 at full throttle, I still get erroneous indications, I have to jump in with my old 1033 to get proper readings.

Finally, if I were going to make something like this, I'd probably consider a device that didn't require calibration.  The reason that the HCT123 design requires calibration is the tolerance of the triggering voltage level for the chip.  I'd be looking at a design that didn't need calibration.

Aren't you sorry you asked?

Yep, I sure am! 

Seriously, I appreciate all the comments so far, exactly what I was looking for.  I had not considered any of these issues, so it kind of looks like my little project may have gone up in smoke. I may still order a small batch of boards though, just to experiment with. If nothing else they will go right along with a few others I have that make interesting paperweights! 

Rod

We are never too old to learn something stupid....

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