It's much smaller than a cigarette pack. It adds a 3.5mm cable coming out of the ESM1 and there are two resistors (which will need a small vector board) in the line between the ESM1 and soundcard.
I'll need to build one and test it to see how accurately it will record PLC level. This is a 60Hz signal and some soundcards may not do too well with that.
You may need a lot of free disk space to record overnight - I haven't analyzed that yet. Nor do I know if there are limits on the size of .WAV files that can be viewed & edited.
What happens if you move the ESM1 meter head near the transformer, as in mounting both the head and a power supply inside the same box and having just a line cord extend from the unit? One "ease of use" feature of the Monterey that I really like is the built-in power supply. The line cord is typically easier for me to find a ready outlet for than the whole wall wart. I use a 6' extension cord right now, but if I am going to be modding the ESM1, that a mod I'd consider doing at the same time because I've been thinking of mounting the "head" on a little slotted hinge so I can angle the readout to see without hands. It's like my doctors. "As long as we're going in to fix your cruxus whatis, why don't we do a little debriding?" In for a penny, I guess.
No rush, but I certainly like the idea of a having a different "EKG" for each circuit in the house.
I may actually want to send a known reference pulse through each transformer in round robin fashion and save the files for visual or computational analysis. If the standard J1 ON starts to show unusual noise or a drop in amplitude, it should be obvious in a comparison view.
What would happen if I recorded in MP3 and converted back to WAV format? would the loss be noticeable? Disk space wouldn't be as much of an issue that way.
Interesting. I would have thought the wall wart would attenuate the high frequencies we were looking for.
By the way, I built the scope circuit in the AppNote above. It seems to work, although I won't be able to test it until tomorrow. I also built in the 32KHz high pass from the AppNote to play with.
I tested the effects of the wall transformer on the meter extensively when the ESM1 was introduced (and my review here savagely attacked on those very grounds). I found no effect. My test setup usually has the wall transformer in a powerstrip on a work bench with the meter sitting atop the transformer and my Scope-Test2 or other filter plugged into the same powerstrip.
I have no idea how lossy MP3 might be in this case. I use Loop Recorder for tests like these and it only records .WAV files. All I can suggest is that you experiment.
Until I test it I don't know whether the soundcard will record the higher frequencies that are beyond the audio range. Since we're sampling at a rate well below the Nyquist limit, we'll see an aliased noise signal if it's not filtered out first. My Audigy soundcard can sample at 96Kb/s (although Loop Recorder does not go that high) but higher frequencies may be filtered before the sample is taken. This is, after all, a $1.98 solution (1 audio cable, 2 resistors) which, while it may not be the ultimate piece of PLC test gear for all conditions, it should prove useful to anyone who already has the ESM1.
That's good to know. If it all works out, I will remount everything in a different case with a single, very long line cord.
I see. IIUC, the X-10 signal's frequency (120KHz?) is way outside the normal audio range so eventual success is going to depend a lot on the characteristics of the sound card and recording software. Are there any electronic tricks that can bring the frequency down? Halving the playback speed would reduce the frequency of a normal audio signal but that wouldn't work here because the card may not be able to capture the higher frequency to begin with. No magic frequency divider in a IC package or does that mean lots of additional support circuitry and isolation issues?
No, no, no. Look at the oscilloscope screenshot. The ESM1 demodulates the
120kHz X10 bursts and we see a ~1mS, 5V baseband pulse on pin 18 with a maximum frequency of 60Hz. This and the 60Hz ZC signal on pin 13 are well within the frequency response of the soundcard. I have frequently recorded the baseband output of RF and IR receivers and the soundcard has no problem with the 8.8mS X-10 RF start pulse (and about the same as the 60Hz on pin
13) nor with the less than 1mS pulses used in the bitstream so we should have no problems with ZC of the 1mS X-10 pulse. Look at the bottom picture here...
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Pin 18 is an ADC pin and the amplitude of the pulse in the X-10 window is approximately proportional to the signal level on the powerline. The soundcard will record differences in this level but we have no fixed reference and will have to make comparisons between the recorded amplitude and number of ESM1 bars to "calibrate" the .WAV file. And, it's possible to edit the .WAV file to increase/decrease amplitude, filter out noise, etc. so it really depends on the desired end result.
You might also look at...
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bearing in mind that peak-to-peak levels are ~2.8 times the RMS levels given.
We need to limit the amplitude at the input to the soundcard (the resistors lower it to ~1V MAX) to avoid clipping which will remove any amplitude information. We need to make sure that we still have some headroom when pin
18 is @ 5V.
I'm not sure why the 140kHz noise signal is showing up on my scope _OUTSIDE_ of the 1mS window but suspect the firmware sets pin 18 low to drain the capacitor that is part of the peak detector that demodulates the 120kHz. It's only that noise outside the 1mS window (which I'm not sure I understand) that I'm not sure the soundcard will "hear". If it makes it past any input filters, it will be sampled and aliased so we'll see something similar to the oscilloscope screenshot (where the sampling rate is only
20Kb/s). I'll try to build a prototype today or tomorrow and test everything.
IOW, the .WAV file should be a reliable way to record/analyze X-10 codes but may not be as useful to analyze any high frequency noise that may be present. What do you expect from adding a bit of wire and two resistors? ;)
I'm still not 100% sure where those 2V, 140kHz noise bursts are coming from but the pre-ELK ESM1 shows 1 bar while my monitor is awake and no bars when it goes into standby. I'm fairly certain it's on the powerline as I left the ESM1 in the exact same location but used an extension cord to power it from another circuit and the noise disappears even with the monitor awake. Until proven otherwise I'll blame it on the usual suspect but I'm not ruling out a ground-loop. Here's a picture of the 3.5mm cable...
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A few inches of the female end will hang out of the ESM1. An adapter with the resistors will plug into it and into the line-in input. When unplugged the ESM1 operates as it always did. (I expect it to operate just as well when connected to a soundcard but this way plays safe.)
OK, I have the prototype running. It does show the 140kHz noise, even at the lowest (8Ks/s) sampling rate although with no detail at that resolution. Still, it's an indication that there's something on the line that needs further investigation. I'm not sure we need the resistors so it might get even simpler and a bit cheaper.
I've added a screenshot showing a section of the .WAV file at...
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A 10 hour .WAV file is about 2.2GB so I'm not sure it's all that useful for overnight recording but it's also possible to design a small PIC-based module to plug in instead of the soundcard with enough smarts to output just the X-10 bits via RS232 so a 10 hour file becomes much smaller and much easier to decipher. I was discussing adding RS232 output to the ESM1 with Paul Beam (the designer) before ELK bought the rights to it. I sure wish I had thought of this then.
Damn - that 60Hz hum (ZC squarewave) from my PC speaker is starting to annoy me. You can also hear the X-10 bursts so this may prove to be a handy troubleshooting tool.
I have to get my network back up before I can finish documenting things. I have pictures of the ESM1 board with the added cable but my camera software is on a different machine from my graphics editing software and HTML editor.
Well, it works. And works well. I found a bad battery backup and a bad GFCI outlet. It took a lot of breaker flipping, but watching the change in noise and signal levels was very helpful. One by one the changes made by bringing a new circuit on line could be monitored visually. Very helpful.
As I noted earlier, I don't know whether you would lose detail but it's worth a try. The latest version of LoopRecorder defaults to .WMA which is a compressed format. Also, you can record the signals in mono which will add the two channels together but cut the file size in half. This gets the file down to sizes more easily managed for overnight recording.
The noise that I see here turns out to be more complex than I first thought. There is something on the powerline just before ZC (and after the third X-10 burst) plus the ESM1 is affected by EMI from my Dell CRT monitor. With the ESM1 plugged into an extension cord that is plugged into a different outlet, there are no bars until I move it near the monitor and then I see 1 bar. I don't think this is having any effect on the recorded signal - all of that noise seems to be related to the mystery 60Hz pulses.
I've added another screenshot to the web page showing the powerline through the oscilloscope adapter described in Microchip's appnote AN236. It shows the mystery noise as well as an X-10 signal.
I may play around with a similar circuit fed by a 12VAC wall transformer to allow soundcard recording with no need for an ESM1. It might make a worthwhile addition to the troubleshooting arsenal and won't have the frequency limits of the ESM1.
Just wanted to post my resolution - I was getting some very intermittent behavior and it seemed that the addition of the water heater and/or its wiring was the last straw. Got varying results using different repeater/couplers I had, testing at various points inside the main breaker panel and at various test points around the house.
Decided to try Jeff's device - happy to report that everything seems to be working very solidly with the addition of the XTB - I can now illuminate the front of our house *AND* take a bath!
Thanks again for your generous help, all the best...
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