Nuts and Volts - March 2015

READER-TO-READER TECHFORUM

>>> QUESTIONS

X10 Cable Build

I have an early X10 Home Control Timer (Model CP-290) to which I have lost the programming cable. Does anyone know where I can get the pinout so I could fashion my own replacement cable?

#3151 Leigh Guzman Oxnard, CA

Lightning Protector

In a recent thunderstorm, a nearby lightning strike took out some of the electronics at my neighbor’s house. Is there anything a DIY'er like me can build to protect my delicate electronics — other than unplugging everything? Something with MOVs maybe?

#3152 Matthew Hodges Wichita, KS

PCB Chem Disposal

I’m interested in photo etching copper-clad PCBs. Most guides don't say what to do with the chemicals when I'm done. Do I just pour them down the drain or will it hurt the environment (or my pipes?).

#3153 Gerardo Rios Phoenix, AZ

Arduino Remote

My Sony BluRay/DVD player came with a very complicated remote control. I don't need half the buttons! Is it possible to make a simplified replacement remote using an Arduino and simple buttons with an IR-LED?

#3154 Terence Rodriquez Raleigh, NC

[#2152 - February 2015]

Battery Dilemmanator

About three years ago, I put together a 1.5 volt battery eliminator using a wall wart feeding into an LM4120 regulator to power the clocks I have around the house. The clock that I started with is a Howard Miller mantle clock that a company awarded to me for busting my ass for 25 years.

After installing the eliminator, I set the clock to the time of my crack atomic wristwatch and let'er go. The clock ran for almost three years with phenomenal accuracy, matching my watch within a few seconds but finally died — probably from exhaustion — having gotten no rest between battery exchanges.

Well, I thought, what are you waiting for. Get with it with the other cheap clocks cluttering up our house; so, I did. To my amazement, none of the clocks running on the eliminator could keep time anywhere near what could be termed accurate — no matter how much I adjusted the voltage (usually, the clocks ran fast).

So, what gives? Why does a battery work and my eliminator won't?

#1 I recommend looking at the LM4120 output with a DC coupled oscilloscope and checking for noise or voltage drift, either short-term or long-term. I think you will see the problem.

John Keller via email

#2 Without more information, it's difficult to give a definite answer, but here are three possible causes to check:

1. Is the output voltage correct? Check with a DVM; anything from 1.35V to 1.6V should be okay for LCD or quartz clocks.

2. The power supply has excessive AC in the output, e.g., a bad capacitor. Though you could check this with an audio amplifier or oscilloscope, it's easier to just put a 500 microfarad or larger electrolytic cap across the output and see if that fixes the issue.

3. AC or RF leakage from the power supply — either from the mains or from a nearby radio transmitter — is making its way into the clock. The clock circuitry is very low power, so any AC could flip some flip-flops a few extra times per second. To check this, you could make a Faraday cage (e.g., window screening) around the clock and connect it to one side of the supply. This is to satisfy your intellectual curiosity, though it's probably not a convenient way to run a clock.

B. Bresnik via email

#3 First off, I suggest the following:

1. Measure the OPEN-CIRCUIT output of your eliminator before connecting it to the clock you want to run.

2. Connect the eliminator to the clock, then measure the voltage output again.

If the difference between the "no-load" voltage and "load" voltage is more than 0.5 VDC, it's entirely possible your wart isn't delivering enough current to properly operate the regulator. In this case, try a similar-voltage wart with higher current output (say, 1.5-2X of your current wart). This may solve the problem as wall wart outputs tend to droop severely once you approach their maximum current capability, resulting in severe output instability (i.e., the regulator won't "regulate" well), increased ripple, noise on the DC output, and severely shortening the life of the wart (i.e., over-

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