CM11A hangup: Any better products?

Hello Dave,
Well, that's not quite so IIRC. As George said the transmit can be generated by the micro controller in a transmitter. All you need to do is generate pulses of 8.3usec repetition rate and turn them on and off as per the code you want to send. That is very easy to do with a uC and I believe that's how the RR501 works. This pulse rate is controlled by the crystal or resonator that operates the master clock of the uC. This is going to be very accurate.
True, the signal then has to pass the LC circuit. It is, in RF terms, usually a "class C" one-transistor stage where the base is driven hard by a uC pin. The signal will be reduced in amplitude if the LC is out of tune. So it can make sense to also peak this LC circuit to get the most onto the line but it won't change the frequency.
But a lamp module is only a receiver.
Regards, Joerg
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Joerg
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I don't have any problems with low signal level. If yours is that low, I think you need some filters on your signal sucking devices. (see
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The RR501 puts out about 10Vpp. (see
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Even with a few other transmitters on the circuit it still has about 5-6Vpp at my test bench.
I've removed the clipping diodes from a lamp module and captured some scope screenshots using it along with an unaltered lamp module. (see
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Given the input transformer ratio, you would have to have a powerline signal level of about 350mV or less in order to see the peak with an unaltered module.
Joerg wrote:
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Dave Houston
It is ABSOLUTELY so! All of the X-10 made PLC transmitters for which I've seen schematics (and looked at their innards) with the exception of the most recent RR501 (last 7-8 years?) use an LC controlled transistor oscillator. You can see the circuit in the schematics for the TW523, CM11A, CM15A, TM751, mini & maxi controllers. etc. If you need URLs, I can supply them.
PLC transmitters made by SmartHome and other manufacturers may use resonators and generate the PLC carrier with a PIC - I haven't seen many schematics for them.
The most recent RR501 does generate the 120kHz with the PIC _BUT_ the PIC itself uses an LC circuit instead of a crystal or resonator on its OSC pins so it's unlikely to be any more tightly controlled than the others.
The same is true for all of the wireless devices.
Europe now has tighter wireless requirements and most of the X-10 modules used there are fairly recent designs. They do use SAW resonators for the 433.92MHz wireless transmitters but I think the receivers are still LC. I don't believe they have tightened the requirements for PLC carrier so I suspect they still use LC oscillators for that.
Joerg wrote:
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Dave Houston
Hello Dave,
Be careful. Somebody might turn on a vacuum cleaner and the spike could fry the chip if the diodes are out.
I certainly had more than that but not over 1Vpp. The diodes won't clip much at that level.
Regards, Joerg
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Joerg
Hello Dave,
Yes, do you have the URL for your version of the CM11A?
IIRC mine has a fixed resonator. A tunable LC would be more expensive in production.
I know. Those are a pain, hardly adjustable. I found some of the key chain ones all over the map so we quit using them.
Regards, Joerg
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Joerg
John Galvin reverse engineered a partial CM11A schematic. It's at...
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It includes the oscillator.
I think if you look at your RR501 you'll find it uses one winding of the same model transformer as is used for the input as the L with a couple of 27pF caps. They use so many of the transformers, they probably only cost a few cents. They assemble them in mainland China where production costs are nearly nil. After all, they tune the wireless devices by bending the single wire loop used in its oscillator.
Joerg wrote:
Reply to
Dave Houston
Hello Dave,
This looks way different than mine. I have to look for the schematic tomorrow. If there were no crystal or resonator how would it ever be able to keep time? Mine holds to within a few minutes a year and temps range from 65F to 95F.
Regards, Joerg
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Joerg
Yes, that's it.
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clemslay
| This looks way different than mine. I have to look for the schematic | tomorrow. If there were no crystal or resonator how would it ever be | able to keep time? Mine holds to within a few minutes a year and temps | range from 65F to 95F.
The CM11a does employ a resonator for the PIC's clock, but it uses a separate free-running LC oscillator to generate the 120kHz carrier. (That's the oscillator in the schematic.) The TM751 and the current RR501 generate the 120kHz carrier from a PIC output, but the PIC's clock itself is an LC oscillator. The TW523 and the original RR501 use free-running carrier oscillators much like that in the CM11a.
Dan Lanciani ddl@danlan.*com
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Dan Lanciani
The CM11A keeps time using the 60Hz line frequency. The RR501 does not keep time.
Joerg wrote:
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Dave Houston
It doesn't matter whether they clip a little or a lot - the positive and negative peaks are still clipped. The point is that "peaking" the signal in the manner you describe is impossible.
Reply to
Dave Houston
Hello Dave,
It is possible. When the diodes conduct a wee bit you will still have a very noticeable increase and decrease when turning the core. Just try it out. Only when they do a "hard clip" will that become hard to see.
Regards, Joerg
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Joerg
Hello Dave,
It can't do it always. Mine also keeps the time when the power is out and it runs on the four backup batteries. One of them that I programmed for a friend even kept time while sitting in the trunk of his car for weeks. That is nearly impossible with LC.
Regards, Joerg
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Joerg
Hello Dan,
Interesting. I wonder why they did that. They could have saved the cost for the extra LC if they used a timer on the PIC to generate the 120kHz. Unless they ran out of timers but then there is still the chance to use a SW timer.
Regards, Joerg
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Joerg
The CM11A has 2 batteries which are used _solely_ to run the RTC when there is no 60Hz power. The CM11A PIC uses a resonator but also uses a discrete LC oscillator for the PLC carrier. CM11As do not keep very accurate time when running on batteries which is why the CM11A starts sending a "power fail poll" as soon as 60Hz power is restored.
Joerg wrote:
Reply to
Dave Houston
Balderbash!
At best, you might see dips below the diode voltage drop but only when you detune the transformer.
Joerg wrote:
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Dave Houston
Hello Dave,
I thought it was balderdash ;-)
A diode presents an amplitude-variable resistor to the circuit. Below 1Vpp (0.5V into the diode curve) that resistance is pretty high here. I have done RF design for more than 20 years now but if you don't believe it just give it a try.
Look at the 4148 graph as an example:
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At 0.5V it sits around 200uA. Not much of a load to write home about.
Again, adjusting to the correct frequency won't significantly improve high signal amplitude reception. It's at the fringes of range where it makes a difference. Actually even a bit above that level since you want the resonant curve concentrating on 120kHz and not on the noise from the margarita blender.
Regards, Joerg
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Joerg
| Hello Dan, | | > The CM11a does employ a resonator for the PIC's clock, but it uses a | > separate free-running LC oscillator to generate the 120kHz carrier. ... | | Interesting. I wonder why they did that.
My theory is that the implementors of the CM11a were familiar with the free-running oscillator design used in the TW523 and decided to adapt it. It was a proven circuit used in other X10 products as well.
| They could have saved the cost | for the extra LC if they used a timer on the PIC to generate the 120kHz.
Does the 16C58 have the capability to route a timer to an output pin? When I wrote the enhanced version of my replacement firmware for the RR501 I used a timer, but I had to swap some pins around to I could send it out via the PWM block of the 16F628 (not doing actual PWM, of course).
| Unless they ran out of timers but then there is still the chance to use | a SW timer.
I used a software loop for my basic version of the replacement RR501 firmware and it requires a pretty short loop. (I assume the real RR501 & TM751 code works the same way.) I don't think you have a lot of flexibility for the CPU clock rate if you use this approach (or even if you use a timer). The RR501 (and, I assume, the TM751) uses a ~3.84MHz clock to make the carrier come out right. The CM11a uses a 4MHz clock. Perhaps there was a conflict between the clock needed to make the bit-banging serial easy and the clock needed to make the carrier generation come out right. Or maybe they didn't want to tie up the CPU during burst generation. But I still like my convenience-of-familiarity theory best...
Dan Lanciani ddl@danlan.*com
Reply to
Dan Lanciani
Hello Dan,
That could very well be but it would be pretty sad. Engineers are supposed to embrace new concepts when something can be realized at less cost.
Frankly, I don't know the PIC series much. But it would surprise me if it wasn't possible. Pin swaps may be needed. Timer-based outputs are pretty easy on most uC like the MSP430 series even though they often do not have a dedicated PWM block.
It can be a challenge to perform proper RS232 timing and 120kHz. However, since the amount of data exchange between uC and ActiveHome is quite minimal they could have chosen a very slow speed. Then it would be easier to fall into the tolerance range of even do it purely in SW.
Regards, Joerg
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Joerg
| Hello Dan, | | > | > The CM11a does employ a resonator for the PIC's clock, but it uses a | > | > separate free-running LC oscillator to generate the 120kHz carrier. ... | > | | > | Interesting. I wonder why they did that. | > | > My theory is that the implementors of the CM11a were familiar with the | > free-running oscillator design used in the TW523 and decided to adapt | > it. It was a proven circuit used in other X10 products as well. | | That could very well be but it would be pretty sad. Engineers are | supposed to embrace new concepts when something can be realized at less | cost.
Of course, they might have done the analysis and decided that this solution _was_ the most cost effective. Typically X10 does a pretty good job of "value engineering" in spite of what its competitors sometimes claim.
| > | They could have saved the cost | > | for the extra LC if they used a timer on the PIC to generate the 120kHz. | > | > Does the 16C58 have the capability to route a timer to an output pin? When | > I wrote the enhanced version of my replacement firmware for the RR501 I used | > a timer, but I had to swap some pins around to I could send it out via the | > PWM block of the 16F628 (not doing actual PWM, of course). | | Frankly, I don't know the PIC series much. But it would surprise me if | it wasn't possible. Pin swaps may be needed. Timer-based outputs are | pretty easy on most uC like the MSP430 series even though they often do | not have a dedicated PWM block.
As far as I can tell, there is no obvious way to route the 16C58's TMR0 (the only one it has) to an output pin. I don't think this function is typically available on 16x PICs. I was able to do it only by using that PWM block in basically a pass-through mode, and a PIC with a PWM block may not have been available (or cost effective) when the CM11a was designed.
Dan Lanciani ddl@danlan.*com
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Dan Lanciani

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