Making an X-10 lamp module immune to dimming

--snip--

Precisely. Now, to complicate things a bit, there are loads for which the zero-current point does not coincide with the zero-voltage point (reactive loads like electric motors, for example). In that case, the triac may not turn off at all. There are tricks to deal with that circumstance.

My pleasure.

Isaac

--snip--

Precisely.

It will not conduct again until the proper amount of gate current is applied, while there is a voltage across the device.

Mostly, it's the voltage drop across the chunk of silicon that forms the triac, although some of it may be due to the tiny wires that connect the chip to the external leads.

A transistor is a three-layer device (NPN, say); a SCR is a four-layer device (NPNP), and a triac comprises five (NPNPN or the other way around). Interestingly, because of the way thyristors work, even though they have more layers than transistors, the voltage drop across one when conducting is lower.

But still, whatever that drop is, multiplied by RMS current that is flowing, creates heat.

If you think about it, the worst case is when the device is "half on", because the voltage drop is much larger. One reason to use a triac or SCR instead of a transistor is because they sort of "automatically" go through that halfway state very rapidly. Another is that the voltage drop when conducting is lower.

Isaac

I think that's rather out of date. Mantles have not contained thorium for a long time (at least, not in the UK).

My bad again. Should have said "Stays on until the zero crossing is reached."

One chop per "hump" - I can remember that. It sounded so plausible that a lot of little chops were possible, especially when Isaac reported that there were additional (although unused) pulses on the gate line beyond the triggering pulse. It also sounds like the triac process is something of an avalanche-like process: easy to start with very little energy required but hard to stop when large amounts of energy begin to flow.

I used to think triacs and thyristors worked the same way, but I recall that my Vivitar 283 fossil flash is able to meter out very short pulses from a large capacitor by using a photoreceptor of some sort that can measure and react to flash intensity. I'll see what Google has to say . . .

Makes sense to me!

Is that mostly an "area under the curve" sort of issue?

I'll take a look. Thanks!

-- Bobby G.

OK - this is getting clearer. It doesn't conduct unless "goosed" by gate current and once it's on, the gate current becomes essentially irrelevant until the after the AC half cycle ends and the reversal of polarity shuts off current flow through the triac.

Are there other devices that can interrupt current flow with a gate trigger?

Right. This looks very much like an "area under the curve" sort of problem.

"rechopping"

My "one chop per hump" interpretation. (-:

I thought that any signal other than the one you wanted could be considered noise.

I guess it's time to finally unbox my Radio Shack pen oscilloscope.

Too bad. What's a large number? There's a lot of headroom with 256 discrete X-10 addresses, even if you're controlling a modern home.

Interesting. I assume that with X-10's parsimonious Scotch heritage that they decided that as long as it didn't have a negative impact on performance, they didn't need to add any circuitry to filter it out.

This sounds like one reason that circuit designers are always tweaking the values of capacitors and resistors between board versions: to optimize the various design trade-offs. (-:

It seems as if the R/C circuit is one of the most common electronic "building blocks."

I've been stripping components for a long, long time. When something like a stereo breaks, I put it aside until it's obsolete (that wasn't really the plan, but that's what always happens). Then I strip out the more useful looking parts. Now, perhaps, I can finally *do* something with them. I've been toying with the idea of making an interface to Jeff's XTB to read the raw data bits from the line into a data file. He assures me that it's as easy as pie, but I am not so sure. The problem is that my meager bitwhacking and soldering skills stand in the way! I think first I will try to trace and document the lamp module as thoroughly as I can. I'll do that in a separate thread after a do some searching to make sure it hasn't already been done to death. Something tells me that by tracing the circuit through, I'll pick up a lot that didn't sink in just reading the protocol docs.

Thanks again for all the help.

-- Bobby G.

> ty-car/

Probably not here either. I do believe that they are still using radioactive materials in smoke detectors, although that could be woefully out of date information, too. Thanks for the update. Now I get to unlearn a fact I learned while trying to learn other facts. Unlike books which usually at least have a copyright date, there's an awful lot of undated information floating around on the net.

-- Bobby G.

That explains a few things, especially why dimmers get very hot when dimming at some levels but not others. What I am trying to say is that the heat output curve looks very unlike a resistive dimmer in the same circuit.

Thanks!

-- Bobby G.

I'm going to have to trace this out through the schematic. Do you know of any tools that do a "schematic debugging" the way some software debugger tools work where each line of code executes in a window that displays variable states, etc? I've heard designers talk about simulators but I don't know what they use or how it works. I would like to see something that would tell me what a voltmeter/scope/logic probe would see at a particular point in the circuit for each state change. Not sure I explained that well . . . Anyway, so you're saying if I were to put a probe on that line going to the triac gate, it would be DC pulse; positive when applied to the first half of the AC cycle and then negative for the second half?

I'm confused again. If I applied the probe on the unmodified mod, would I only see positive pulses?

Slowly, it's becoming more clear how these things work.

Neat. The whole concept of AC current is pretty interesting.

I think I have a bit of reading to do but I am thinking the lamp module is a small enough device to trace out thoroughly. Maybe I can even bring myself to trying the mod in question to make them into "dim-free" devices.

Thanks for the explanations. They might even sink in - eventually. (-:

-- Bobby G.

That's right. No matter how fast the device switches on, making the transition at the peak of the half-cycle is going to take longer than when it's near one end or the other. Hence, more heat is generated.

Isaac

Yes. There are gate-turn-off (GTO) thyristors:

Close, but more complex, because the load (assuming an incandescent lamp) is not constant. The resistance of a lamp filament is lowest when it's cold (which is why a burn-out so often occurs when it's switched on), and rises as the filament heats up.

That's a simplistic definition, although it sometimes works.

That National chip (an LED bar generator) has ten outputs, and it can be hooked up sort of like a ten-value A-to-D converter. Having to use an X-10 module for each and every sprinkler valve would work, but has even more problems -- not least of which is the tendency of the things to turn on for no evident reason ("noise" if yo will).

Yup.

Well, yes, but usually a *real* designer will have a good notion of what values to use and not have to try a bunch of things to see what works. Changing a board layout can slightly alter things like the capacitance between adjacent traces, and that can cause instability, especially if the original values were determined "experimentally" by someone who didn't understand worst-case design, margining, and so on.

Yes, it is. Both components are cheap, and easy to get in a wide range of values.

Here's an interesting item: Of all physical units (weight, volume, current, voltage, heat, ...) resistance is available over by far the widest range, easily from under a micro-ohm to over a hundred megaohms

-- say fourteen orders of magnitude. That's why electrical simulations of other phenomena are so easy.

Isaac

| > | As I looked at the mod schematic, I realized that the switching was | > | occurring without any polarity reversal of the trigger. | >

| > No, you were right the first time. The direction of the gate current is | > reversing in step with the line, keeping the triggering in the more | sensitive | > quadrants. | | I'm going to have to trace this out through the schematic. Do you know of | any tools that do a "schematic debugging" the way some software debugger | tools work where each line of code executes in a window that displays | variable states, etc?

No, but some of the simulators might be close.

| I've heard designers talk about simulators but I | don't know what they use or how it works. I would like to see something | that would tell me what a voltmeter/scope/logic probe would see at a | particular point in the circuit for each state change. Not sure I explained | that well . . . Anyway, so you're saying if I were to put a probe on that | line going to the triac gate, it would be DC pulse; positive when applied to | the first half of the AC cycle and then negative for the second half?

It would be a more complicated waveform, but more-or-less yes (and for some definition of "first" and "second") for the modified module.

| > The unmodified module uses its own DC supply to drive the gate | > current independent of the line polarity. Using the more sensitive | quadrants | > (or, in general, using two quadrants with the same sensitivity) keeps the | > triggering times as symmetrical as possible minimizing the DC component in | > the output. | | I'm confused again. If I applied the probe on the unmodified mod, would I | only see positive pulses?

The module uses a negative supply, so only negative. Keep in mind that the zero-volt reference of the module is the hot side of the line, so you have to be careful with such measurements.

| I think I have a bit of reading to do but I am thinking the lamp module is a | small enough device to trace out thoroughly.

It's small, but it's also an exercise in clever cost reduction. The aforementioned use of the hot side of the line as a logic zero-volt reference lets them drive the triac easily without isolation, but it can be confusing and dangerous if you don't understand what is going on. It would not be my first choice to learn circuit analysis...

Dan Lanciani ddl@danlan.*com

So that's how my auto-thyristor flash works!

I see

I'm a simplistic guy. (0: I assume the anything that is non-random shouldn't really be called noise.

Indeed. The only (marginal) solution for me is double-stacking modules. So far, only operator error has inadvertently activated something I've got "double-stacked" appliance modules but I still would be reluctant to control water valves without some other independent verification of operation.

Good point.

And now there's a fourth basic component: the memristor! (The other three are resistors, capacitors and inductors.)

"The newly discovered circuit element - called a memristor - could enable mobile phones that can go weeks or longer without a charge, PCs that start up instantly and laptops that retain your session information long after the battery dies. It also could challenge flash memory: the HP discovery would be faster, use less power and take up far less space than today's flash."

-- Bobby G.

I think so, but sometimes it can be *really* hard to tell the difference (cf. "pseudorandom"). Pseudorandom patterns are regularly used for encryption. If they were *truly* random ,they wouldn't be very useful, but if their pattern could be determined, even with great effort, they would be worthless.

Isaac