The low-down on Tomix CL

[CaptOblivious]

The Tomix cleaning car provides a unique view into Tomix's CL Lighting system, because unlike any other set they make, it gives the option to control the motor with a plain DC signal, or with a CL signal. Which means, you can trace the circuit board to see what components are on it, and which ones get left our or added in as the switch moves.

Now, the givens: We all know, although I have no idea how, that CL uses a high frequency AC signal superimposed on the throttle's DC signal. An educated guess suggests that this works via a PWM signal that is biased by the DC setting. That is, if the throttle is set to 0%, and the CL set to 50%, then a square wave with a peak of 6V and a trough of -6V is sent out. The peaks and troughs cancel each other out, so most DC circuitry sees nothing. But the CL circuitry sees it as 6V? How?

The Tomix circuit board has 4 components: A filter capacitor, to prevent spikes to the motor, a bridge rectifier, which ensures that the motor only turns forwards even when the throttle is set to backwards, a tiny smd component which is unmarked, and may be a capacitor (why?) or a resistor, and finally, a big electrolytic capacitor (marked CS 4.7 35V; does that make it a 4.7uF capacitor?), which is the only component that gets added when the switch moves from "ON" to "CL-Power". See attachment 1 ("ON") and 2 ("CL-Power").

Theory: The cap and the resistor bridging the motor tabs form a passive differentiator circuit, AKA cheap-ass high-pass filter. It filters away the DC signal, leaving only an unbiased high frequency AC signal. The bridge rectifier ensures that the remaining PWM signal is entirely positive. What gets sent to the motor then is a high frequency PWM signal that does not depend on the value of the carrier DC signal.

If I'm right, then there's nothing here to interfere with DCC installations at all. I.e, the necessary circuitry to get a loco to work the CL is minimal, and should have no impact on any decoders attached to it. Also, it makes it easier for us to design CL circuits to make non-CL trains work with CL, if those are our druthers.

Any thoughts?

[Martijn Meerts]

The capacitor is a so-called "reservoir capacitor" or "smoothing capacitor". All it does is smooth the DC that's output by the full-wave rectifier bit (the 4 diodes). The entire circuit converts AC to DC and smoothens the DC. The resistor is a protection to make sure the capacitor doesn't store too much. (In larger circuits of the same kind, the capacitor can have a lethal discharge without the resistor.)

Without the capacitor, the lights would go on and off real fast because there're still a waveform. The difference between the AC and DC waveform, is that the DC one inverts the negative waves into positive ones: http://en.wikipedia.org/wiki/File:Rectified_waves.png.

The capacitor turns the wave into something that looks more like http://en.wikipedia.org/wiki/File:Reservoircapidealised.gif

[NozomiFan]

The Tomix cleaning car provides a unique view into Tomix's CL Lighting system, because unlike any other set they make, it gives the option to control the motor with a plain DC signal, or with a CL signal. Which means, you can trace the circuit board to see what components are on it, and which ones get left our or added in as the switch moves.

Now, the givens: We all know, although I have no idea how, that CL uses a high frequency AC signal superimposed on the throttle's DC signal. An educated guess suggests that this works via a PWM signal that is biased by the DC setting. That is, if the throttle is set to 0%, and the CL set to 50%, then a square wave with a peak of 6V and a trough of -6V is sent out. The peaks and troughs cancel each other out, so most DC circuitry sees nothing. But the CL circuitry sees it as 6V? How?

The Tomix circuit board has 4 components: A filter capacitor, to prevent spikes to the motor, a bridge rectifier, which ensures that the motor only turns forwards even when the throttle is set to backwards, a tiny smd component which is unmarked, and may be a capacitor (why?) or a resistor, and finally, a big electrolytic capacitor (marked CS 4.7 35V; does that make it a 4.7uF capacitor?), which is the only component that gets added when the switch moves from "ON" to "CL-Power". See attachment 1 ("ON") and 2 ("CL-Power").

Theory: The cap and the resistor bridging the motor tabs form a passive differentiator circuit, AKA cheap-ass high-pass filter. It filters away the DC signal, leaving only an unbiased high frequency AC signal. The bridge rectifier ensures that the remaining PWM signal is entirely positive. What gets sent to the motor then is a high frequency PWM signal that does not depend on the value of the carrier DC signal.

If I'm right, then there's nothing here to interfere with DCC installations at all. I.e, the necessary circuitry to get a loco to work the CL is minimal, and should have no impact on any decoders attached to it. Also, it makes it easier for us to design CL circuits to make non-CL trains work with CL, if those are our druthers.

Any thoughts?

Wait, what are you talking about?
I've read this over 3 times and I still can't figure it out. CL, high frequency, DC signal WHAT IS THIS!

[CaptOblivious]

CL is a mystery we've been trying to puzzle through. Here's the deal:

Many Tomix throttles have two controls: One for the motor, and one for the lights. What, you can control the lights independently of the motor with a plain old non-DCC throttle? I hear you asking. Yes. Yes you can. Tomix calls this "CL" for "Constant Lighting", and it's pretty awesome. But it only works with trains specifically designed for it, which is pretty much everything Japanese these days, including Kato.

Question 1: How could CL possibly work? Answer: It does something kind of like DCC, by sending a signal superimposed over the DC voltage. Kind of like how FM radio works. The signal can be filtered from the base voltage, or the voltage from the signal, and so you can use it to power lights independently of the motor.

Question 2: What do you have to do to a loco to make it work? Apparently not much. With bulb lighting, there are some small components you have to include, but apparently with LED lighting, you don't have to have anything extra. Which is why most Kato units work with CL.

Question 3: Why does the Tomix/Atlas track cleaner have a different setting for CL power? That's been bugging me for quite a while, until I took the thing apart. It's still a bit of a mystery, because I don't have a CL capable throttle. I had thought it was so that you could choose to power the cleaner from the CL controls, rather than the regular motor controls, so that the cleaner could be operated independently from the loco hauling it. If that's the case (could someone who has a CL throttle confirm this for me?) then the circuitry inside the cleaner is a huge hint as to how to answer Question 2 in any detail, because it has a regular DC circuit, and an independent CL circuit. So it gives a handy way to make comparisons, and deduce what must be different.

The long view is this: We know that putting a DCC equipped loco on a CL-powered track is bad news. And we wondered if installing a DCC decoder into a CL-capable loco could cause problems for the decoder. Now we know, with certainty: Nope, there is no difficulty in installing a DCC decoder into a CL capable loco.

Does that help at all?

[Toni Babelony]

Thanks for the explanation on this subject. I've been bugled by it for a while, but never really cared about it.

[quinntopia]

I don't understand most of this, but I get the final point: We should be fine with installing decoders in Tomix.  This is good news as I have been skeptical of adding any of them given some of the concerns I've heard from others on this issue.

One question I have....do Tomix throttles deliver any sort of unusual 'signal' (beyond their high end models)?  What I mean is would the Power Unit N-1 http://www.1999.co.jp/eng/10016994 cause any sort of damage or weird things to happen to locomotives other than Tomix?  I suppose if they don't have the seperate CL/lighting control you mention, they are more or less traditional hobby transformers.

[CaptOblivious]

I don't understand most of this, but I get the final point: We should be fine with installing decoders in Tomix.  This is good news as I have been skeptical of adding any of them given some of the concerns I've heard from others on this issue.

One question I have....do Tomix throttles deliver any sort of unusual 'signal' (beyond their high end models)?  What I mean is would the Power Unit N-1 http://www.1999.co.jp/eng/10016994 cause any sort of damage or weird things to happen to locomotives other than Tomix?  I suppose if they don't have the seperate CL/lighting control you mention, they are more or less traditional hobby transformers.

I sure hope not, because that's the very throttle I use! Plugged into a North American power outlet, it actually only delivers 11VDC at full throttle, but as near as I can tell, it's a plain old smooth DC signal. Nothing to worry about, but it's going to bring out all the flaws in any less-than-perfectly performing locos. Why? Have you had difficulties with this throttle?

[quinntopia]

Why? Have you had difficulties with this throttle?

No, not at all!  I was just concerned that there might be some extra stuff going on to support their CL features!   I'm using this little transformer as my power source for the tram line, and I really like it!

[Martijn Meerts]

I'm using a 9 volt Marklin Z scale throttle as well as an old and crappy Minitrix throttle for my analog stuff (aka, most trains ;)) The Marklin throttle is excellent, very good control. The old Minitrix one is rather bad though. The knob is old and worn, so there's no longer anything between 0 and about 3 volts =)

[quinntopia]

Okay, here's something I 'discovered'....it turns out that the other output on the back side of the Tomix Power Unit N-1 is NOT an standard 'DC' accessory output (i.e. most transformers have the variable DC output and a fixed DC output for accessories, I assumed this was the case with the N-1).  I don't know what it is, but I should have taken a clue from the "TCS" label above this port that it wasn't a standard DC out.  I imagine this is some sort of special signal for Tomix's TCS system? 

The way I found this out is that I connected this to my auto-reverse unit as the seperate power it requires, and noting would work (zero output to the track power).  After I disconnected the auto reverse from this power source everything ran fine again, but it was very strange.....

[Martijn Meerts]

TCS is their control system. The plug is used for things like their turntable and camera car for example.