Adventures in TMCC & Legacy... Trying to master the 455Khz track signal. I've built the test car, and it is finally working..

cjack posted:

Anyway y'all had me confused.

The HF special in the 200uA DC-current mode has a 1k Ohm shunt or burden resistor.  With no change in the circuit, they can switch the meter to DC-voltage mode which measures the voltage across 51k Ohms.  Readings of 30-40 uAmps using the 200uA DC-current mode would instead be 1.5 - 2.0 Volts in the DC-voltage mode. 

The reality as I see it is simple.  It doesn't matter what units the meter is measuring (voltage, current, widgets, etc.); the readout gets larger and smaller proportional to the received 455 kHz signal.  And all this occurs over a wide range making it a useful and remarkably inexpensive tool.

Yes, if I were doing it I'd prefer the Voltage measurement mode...but I'm not doing it.  I'd say that ship has sailed and the standard has been set.

Matt Makens posted:

If it came out of the box it might be bad from that Genesis I had to upgrade. Try a different board 

Thanks Matt. That was in a bucket with your name on it. Not sure if I have another. We had ordered a couple of ERR's did they all get installed? I thought there was one for that Lakawanna switcher. You did the MTH TC&W, the MTH CP switcher. I thought there were 3. That board may be from the Genesis. I haven't got any spares that I know of. CRAP.

stan2004 posted:

cjack posted:

Anyway y'all had me confused.

Yes, if I were doing it I'd prefer the Voltage measurement mode...but I'm not doing it.  I'd say that ship has sailed and the standard has been set.

Alea iacta est, eh?

cjack posted:

Alea iacta est, eh?

Translation: "The train has left the station"

Test the board in an engine first, then install it in the car.  Making sure you have control of the light will insure the board is working in the test rig.

gunrunnerjohn posted:

Test the board in an engine first, then install it in the car.  Making sure you have control of the light will insure the board is working in the test rig.

Good point John, I'll have to open up an engine to do that. Not my favorite thing, but I can. I'll have to run down to the hobby store and grab the R2LC tomorrow. Project on hold for today, lots of other projects to work on.

Anything new Elliot?  .   Yes or no is good enough. 

Sorry to report Gregg nothing new on this yet. The one R2LC board that I had loose turned out to have been a dud. It had come out of an engine where the whole TMCC unit was replaced.Now I know the rest of that unit was probably OK and it was just the R2LC.

I'm reluctant to grab one out of a good engine, so the plan is to hit the LHS. Unfortunately, the one guy who has access to the parts is only there for a short time on the weekends. I stopped by last Saturday, but my timing was off by a few hours, too early.

The store is about a 20 mile schlep, and I don't like making special trips if I can help it. I have two more shots this weekend, as I have other train activities both days and can just pop in on my way past. If that fails, I'll just order a few online. Seems like a good part to have spares.

This is still a very important project, and needs to get done, but I can be patient about it. There are plenty of other things to do while I wait.

I'll let everyone know when the party starts.

Elliot, what are you going to do with that R2LC dud?  Are these routinely repaired, saved for scavenger parts, or just tossed?  If the latter, would you send it to me? 

I don't run TMCC and don't plan to but this signal-measurement discussion has been going on for years and I'm curious. I suppose I could get lucky and repair the board using schematics I see on the web...in which case I can mess with the signal-measurement pin13 circuit and Harbor Freight meter using a 455 kHz signal generator rather than a TMCC base.  Whether or not I get it running I'd return it - your worst case out-of-pocket would be ~$3 for USPS First Class package shipping.

Stan, in my world they're just tossed. They are machine made with all those tiny components. Even if I could figure out which one was bad, I probably couldn't fix it. I'd be willing to "donate its body to science". Shoot me an email, and I'll send you the carcass.

They are really fixable except for the programmed chip. You can replace drivers, caps, etc. and the rf chip. The SMD is doable for most folks.

Big_Boy_4005 posted:

Stan, in my world they're just tossed. They are machine made with all those tiny components. Even if I could figure out which one was bad, I probably couldn't fix it. I'd be willing to "donate its body to science". Shoot me an email, and I'll send you the carcass.

Email sent.  Check you junk email folder

cjack posted:

They are really fixable except for the programmed chip. You can replace drivers, caps, etc. and the rf chip. The SMD is doable for most folks.

Oh good, glass half full!  Earlier Elliot reported there was no voltage being supplied to the RF chip so I'm hoping it may be something simple in the power supply which I should be able to repair.  My interest is getting enough working to fiddle with the signal-strength part of the circuit.

Well gang, this project is back on!

I finally found a brave and helpful person at the hobby store, who was willing to risk death, and go back in the parts room and get me what I needed, a couple brand new R2LC's. Always good to have a spare. I should be back up to speed on this by mid week. I've been busy with other stuff while I was waiting.

Q: Does this thing need to be programmed for use in this project, or is it just good to go as is?

Stan, the bad one will be in the mail to you in the morning. I'll be interested in hearing what you find.

Given the radio signal for TMCC, is there a ideal recommended antennal length? 

BTW:  I'm making one of these nifty devices too.  Dunno why, since I haven't experienced any serious reception problem areas on my layout.  But just for fun I guess.

455khz?  Given the wavelength of the carrier is around 657 meters, the longer the better!

If you are talking about a signal testing car, my antenna is a horizontal brass rod 7" long.  I see saturated signals of 62 uA at some places, so this antenna may be on the "large" side.

I HAVE A WORKING TEST CAR!!!

I got the pin 13 lead soldered onto the chip of the new board. Makes a world of difference. The light even works. The meter is reading 36 to 41 on the short section of track I dragged it over. There's a slight problem with the chassis I used, as it is leaning slightly and is making intermittent contact with the ground. Physical problem, not electronic, should be a quick fix.

We're open for business!

Congratulations, Elliot--March is off to a good start!!!

Thanks Carl, but not so fast. I'm going to have to locate another chassis, because this one had the living crap run out of it back at enterTRAINment. The axel bearings are so worn that the side frames are dragging against the center rail extensions on every switch, in a glorious Fourth of July style display. Thank God I didn't fry the new board.

Dale Manquen posted:

If you are talking about a signal testing car, my antenna is a horizontal brass rod 7" long.  I see saturated signals of 62 uA at some places, so this antenna may be on the "large" side.

Dale, could you comment on why you use (or it appears so anyway) a 9V battery to power the R2LC instead of track power?   I realize it allows you to lift it off the track and take measurements anywhere.  I figure a track-powered R2LC installed in a typical engine or accessory car has a steel chassis connected to the outer rail and attendant wiring/harnesses.  It seems this would present a different signal receiver environment, ground plane, shield to the antenna, etc. than a battery-powered receiver on a plastic flatcar bed. 

I'm wondering if the readings will substantially vary depending on the signal-receiver design.  OTOH it may be a your-mileage-may-vary situation where as long as you have a tool to improve your own layout it doesn't really matter if readings compare to another layout...

When you lift it off the track, wouldn't you lose the track common part of the signal?  It would sure be reduced in strength in any case!

Big_Boy_4005 posted:

I HAVE A WORKING TEST CAR!!!

I got the pin 13 lead soldered onto the chip of the new board. Makes a world of difference. The light even works. The meter is reading 36 to 41 on the short section of track I dragged it over. There's a slight problem with the chassis I used, as it is leaning slightly and is making intermittent contact with the ground. Physical problem, not electronic, should be a quick fix.

We're open for business!

Elliot

Good news you got the signal car working.  At the NJ Hi Railers, we found we needed readings in the 40+ range to obtain reliable control of 80-90% the engines.  Steam engines are the ones that need higher signal, due to the antenna they have.  

If you have not already hot glued the pin 13 wire to something, I would do so.  I found it was very easy to break the wire connection to pin 13 if the wire was not secured to something.  

Good luck,

Bob D

NJ Hi Railers 

swise posted:

Given the radio signal for TMCC, is there a ideal recommended antennal length? 

BTW:  I'm making one of these nifty devices too.  Dunno why, since I haven't experienced any serious reception problem areas on my layout.  But just for fun I guess.

 I found that ~ 4"-5" of wire gave the same readings as the typical 1 1/2" - 2" metal antenna, which is found in many engines.  The longer the wire the more signal will be picked up, but I want to simulate what a typical engine would see, so I kept it at 5"

For engines that persist to give you a problem, extending the engine's antenna with wire or 1/2" copper foil will definitely help in the overall performance of the engine.  If you use copper foil, make sure it is securely attached to the sides of the engine with a silicone adhesive.

Bob D

NJ Hi Railers 

Why a battery?  Because that means I don't need a car with a roller pickup and I don't need to worry about center-rail dirt.  That flat car is one of the metal ones, not plastic, and the receiver/battery is grounded to the chassis.

I expect that the readings will only be useful as relative readings.

Thanks Dale, all understood.

OK folks, so I repaired Elliot's R2LC board and have it running with the Harbor Freight meter.  I don't have a TMCC base but am using pro-grade RF signal generator to create modulated FSK/FM signals at 455 kHz.  I'm getting the same "saturated" level as Dale is getting (about 62 uA) so I think I'm good.  Also, with NO 455 kHz signal in the vicinity, I read about 20uA with no antenna plugged into the connector, and about 15uA if I ground the antenna contact.  That seems to square with the 3372 chip datasheet meter sensitivity.  I of course can't test whether the R2LC outputs work since I can't send TMCC commands but as a signal strength meter I don't think it matters.

My next thought is a simple audible circuit that changes tone proportional to signal strength.  So you can listen to the pitch go up and down with signal strength rather than (or in addition to) reading the meter.  As Dale comments, this device is "only useful as relative readings" so when fussing with layout adjustments it seems having a tone going up/down might be useful so you don't have to watch the digital meter readout which might not even be in view if going thru a tunnel or across the room.  Has anyone already done this?  Waste of time?  Comments?

What was bad on the R2LC that there was no signal present at pin 13 on the MC3372?

Just curious...

cjack posted:

What was bad on the R2LC that there was no signal present at pin 13 on the MC3372?

That's an excellent idea Stan, I believe the tone has been suggested before.  I was also thinking of a couple other variations on the theme.  One would be a bar graph on the car so you could see at a glance the signal, and of course the other would be a remote broadcast of the reading so you could see it locally as the car runs around.

The tone is one of the simplest and very effective methods, might just be the ticket.

stan2004 posted:

cjack posted:

What was bad on the R2LC that there was no signal present at pin 13 on the MC3372?

Thanks. 5 v supply?

Well done Stan! You made that look easy. The audible signal idea is interesting, as long as the pitch range is easy enough to differentiate between adequate and substandard levels.

http://www.ti.com/lit/ds/symlink/lm231.pdf ?

Or this...

cjack posted:

Thanks. 5 v supply?

Essentially yes, the 3.3 ohm resistor is in series with the input to the 78L05 5V IC regulator chip.  What thru me for a loop is this version of the R2LC (maybe all do this) has a diode in the ground-leg of the 78L05.  This raises its output voltage by one diode drop or to about 5.7V (instead of 5V).   Elliot said he couldn't read any voltage on the 3372 chip so I knew there was a problem in the 5V circuit...but I had to scratch my head for a bit when I couldn't find a connection between the 3372 ground pin and the 78L05 ground pin!

Big_Boy_4005 posted:

Well done Stan! You made that look easy. The audible signal idea is interesting, as long as the pitch range is easy enough to differentiate between adequate and substandard levels.

That's an interesting point.  As Dale points out, this is a "relative" tool where there's no absolute threshold.  The meter circuit on these chips has quite a bit of variation chip-to-chip so 2 different R2LC boards can give materially different readings for the same signal strength.   I was thinking more in terms of hearing the tone go up and down in real-time as if someone is telling you you're getting warmer or colder.  That is, you really need to look at the recovered TMCC digital signal at the output of the 3372 to know if the signal is good.  Obviously you could have a monstrous interfering 455 kHz signal from wherever that would measure as a high level but be useless.  You are now entering the Twilight Zone of so-called Bit-Error-Rate instrumentation which has its role in the universe but probably not in the world of TMCC.   If I do come up with something you'll be getting it when I return your R2LC so you can be judge and jury!

cjack posted:

Or this...

 

Yes, that's what I was thinking since the 555 has oomph to drive a speaker.  The design problem is whether the 3372's meter output pin with its microamp current-output can drive the 555 without a bunch of additional circuitry.  Additionally, the DC power to drive the 555 and speaker has to come from somewhere.  Burdening the on-board R2LC's 78L05 may be asking too much to drive a speaker so Dale's 9V battery might be the way to go.  Classic case of all ideas eventually degenerate into work!

stan2004 posted:

Classic case of all ideas eventually degenerate into work!

 Or as I'm fond of saying...

Here is my version of a "squealer" for an audio output from the R2LC.  It consists of an inverter/level shifter and a 555 timer chip.  The frequency range isn't really broad, but it is enough to hear changes of RF signal strength.  I am also using my meter in voltage mode for a digital readout via wireless video.  The loudness potentiometer is 500 ohms.  The battery's positive terminal (via a switch) is connected to Pins 4/8.

I needed an acoustical baffle for the rear of the speaker, so I just decided to stick the circuit board inside the a truncated pill bottle that had already donated its closed end to another project.  It is powered off the 9V battery I am using for the R2LC.

I wanted to swap out the Harbor Freight meter for one with display illumination so that my video camera's image would be clearer, but wouldn't you know it, HF didn't have a single one in stock yesterday!  When I go to Camarillo Wednesday, I will go to the main HF headquarters to pick one up.

So now my configuration is complete - test receiver, squealer, meter, wireless video, and a 'scope and one of my Track Signal Strength meters to monitor the output of the Base.

Now what was I going to do with all of this.....?

Cool Dale, but we need a video of your squealer in operation.

OK guys, no more false alarms. The test car is up and running after I replaced the chassis. I finally took my LC+ BN NW2 out of the box and got it going too. I'm ready to take this rig for a spin.

The short test run revealed readings in the 30 - 40 range, and as always when I put my hand near the antenna, the readings jump by about 7 - 10 points. I still wish I could pinpoint what I did to this section to cause the signal level to drop to these unacceptable levels, as it used to work fairly well.

The next logical step is to run the car through some of the areas with known good signal, including the small helix and the upper deck, to determine what an adequate reading is on my layout.

elliot... any new wiring in that area? did things work better prior to adding the lights on underside of that area?

any new construction over it around it enclosing it? any changes to electrical boxes for home and layout area?

is it possible the wire to chicken wire either came loose or a poor connection?

I know may not help but then again something I said might trigger something for you.

[pun] intended here do like dcs folks un-wire things until you find the one wire where that area starts working again, oh now I've done it!  as i chuckle to myself  

good luck and I like that you started test at daytons bluff 

How "new" is that bundle of wires under the track in the photo?  And the control panel, which must have a lot of TMCC "track" signal on all the power switches?

Elliot-

This might not be the case, but sometimes when I "bundle wires" like the picture shown, with multiple over head tracks, I have issues with the TMCC signal...