Surprise X10 signal sucker: LED nightlight

Guy Lavoie

Active Member
I just got my Elk ESM-1 signal tester today and I wanted to solve one nagging problem I had with a specific circuit. After testing signal strength and disconnecting various devices, it turns out that the culprit was a nightlight that uses a LED and a large lens. It then dawned on me that this was not so surprising after all. To drop the 120 volt line voltage down to a voltage that won't burn out a LED, you must add series impedance. A quick calculation with ohm's law shows that to get about 10 mA through the LED (assuming RMS voltage and half wave rectified), you would need to put about 12k of resistance in series with the LED (120 v / .01A = 12000).

Using a 12k resistor would work, but the resistor would be dissipating a bit of heat. Assuming that the 1.5 v voltage drop is negligable for now, 120 V x .01 A = 1.2 watts. Yet the label on the nightlight says 0.1 watts, so its not using a resistor.

The other way to drop the line voltage would be a series capacitor. This has the advantage of not dissipating heat, but by reflecting the unused power back to the power line. The impedance of a capacitor varies with frequency and the impedance decreases as frequency increases according to the formula:

impedence (ohms) = 1 / (2 * pi * f * C)

where f = frquency in Hz and C = capacitance in farads. with this forumula, a .22 uF cap would have an impedance of 12.057k at 60 Hz, to get about the same 10 mA current through the LED when it is forward biased:

1 / (2 * 3.1416 * 60 * .00000022) = 12057 ohms

Now if we calculate the impedance effect that this has on the 120 kHz frequency that X10 uses on the powerline:

1 / (2 * 3.1416 * 120000 * .00000022) = 6 ohms!

Amy wonder why the X10 signal is getting killed?
Detailed explanations like this one should have a place of their own so they are easier to find in the future.

I also received my Elk tester (from Martin). I was having problems with various circuits also.

I found a small tv/vcr unit in a bedroom was sucking signal down to almost a third. I also found my LCD monitor in the kitchen was sucking signal down to half.

All this time I thought it was my undercabinet fluorescent lighting giving me problems there and it turned out to be the Sony 15" LCD monitor instead!

I also found two computers, another TV and a VCR giving me problems as well.

Turned out to be a very fruitfull exercise. I just may keep the tester so I have it full time (so I can test anything new that gets plugged into my home).

Thanks goodness Martin is having a sale on 5 amp signal blocks right now!!

Once I get some more in (second order of them) I am going to test every single item that is plugged into my home.

I tested this by creating an event in Homeseer that sends an X-10 signal every five seconds, then just started checking outlets in the home.

In some cases I had to start turning off circuit breakers to isolate problem areas.

All in all it was a good exercise and hopefully when I am done I will have a more reliable system. I wished there was a way of automating measuring signal strength say every so many minutes (send out a command and see the results) as I get something sucking down my X-10 signal every now and then (not consistent).
Quite some time ago, I obtained a "loaner" meter from Martin. After two days, I emailed him to "charge my card", I was KEEPING it. Haven't looked back, Ilove it.
Man, you are not going to believe this surprise signal sucker, an X-10 Mini Controller made by Stanley (shown HERE)!

Worthington's was selling them for something like two bucks and I bought four of them. They have a lighted pushbutton for the "all lights on" and I'm betting that is contributing to the signal sucking!

Hehe, just a note that the X-10 version of the mini controller (made by X-10) did not suck the signal down.

Oh, by the way, if anyone wants four slightly used Stanley mini controllers let me know and I'll ship them to you!

If you hqve both versions of the "same" model, how about opening them up and comparing the boards visually? There might be just one small capacitor somewhere that makes a difference. It could be educational...
The biggest signal suckers in my house are a rechargable flashlight and some small rechargable emergency lights. Apparently the charging circuits in these lights is to blame. Based on the small size and weight of the lights, I suspect they lack a transformer for dropping the 120VAC line voltage to the low voltage required for charging the batteries. Maybe a simple switching supply instead?

:) Thanks for this posting. I was having a hard time with an LED nightlight. I hooked it up to a lamp X-10 unit and was using it for a little light in the room in the morning. (I get up very early and my wife continues to sleep.) I was never able to get it to work in the plug that I really wanted it in. This past weekend I got a normal (christmas tree light) night light. Now it works great and where I wanted it.

Side note: I was using the lamp unit because I didn't want the clicking noise. Now I'm using the lamp unit because the light puts out too much light. Also I didn't want the light on all the time. I don't even like the phone's LED lights in the bedroom when I'm trying to sleep. KEEP IT DARK!
I have an Elk meter - how do you identify a signal sucker with the meter? Does it show a lower signal strength when an x10 signal comes across?
I have an Elk meter - how do you identify a signal sucker with the meter? Does it show a lower signal strength when an x10 signal comes across?
Just have an X-10 transmit source, measure the strength near it, then go around the house and compare the signal strength levels.

A signal suck will show up with a substantial reduction

You might find some areas where you aren't sure about, then just move the X-10 source around and repeat the process. You can ususally find the source easily

I just had HomeSeer send a signal every five seconds or so and went around the house with my meter. Only had a couple of rooms that required a little bit more troubleshooting.
Seems most modern electronically controlled devices maybe signal suckers or noise makers.
I have seen a reports of new washers and dryers being a problem. Many have found the cell phone chargers can be real problems also.

I have both an ELK ESM-1 and a Smarthome TesterLinc. Both are great to find signal problems.

LED lights also have the problem of not going completely off. Due to many modules having the local sensing circuits small current be enough to partially light them.