DIY X-10 AC Power Sensor

I built this sensor to monitor my X-10 controlled pool pump. Because X-10 controls are normally open loop and not 100% reliable, the pump sometimes fails to activate or sometimes turns on by itself. This sensor provides feedback to indicate when the pool pump is actually on.

The basic idea is that the sensor monitors the AC power going to a device and transmits an X-10 signal that corresponds to the device power state. At the other end, appliance module is set to respond to the monitor signal so that an indicator lamp (a night light style bulb plugged into an a outlet in my kitchen) goes on when the device is on.

The sensor is not limited to just monitoring a pool pump. It can monitor any single phase or split phase device, and the device can be manually controlled or automatically controlled (e.g. by
X-10). The indicator is not limited to an appliance module; it can be a lamp module or another system that can receive X-10 signals (some security systems have this capability). I like to use an appliance module because it makes a nice loud “click” sound when it goes on.

In order to minimize the cost, a stock X-10 mini-controller unit (about $13) is modified to interface to the device to be monitored (the pool pump) power circuit. You should be able to build the complete sensor for less than $20.

Step 1 Get some parts

part list, sensor
(1) X10 "mini controller" known as model PHC01, MC460, etc. (this is a discontinued product, but it's still available).
(1) PIC12F508 microcontroller
(2) 6N139 opto-isolator
(2) 1N4004 400V diodes
(2) 47K 1/2W resistors
(3) 10K 1/4W resistors
(3) 1K 1/4W resistors
(1) 2N3906 PNP transistor
(2) 2N3904 NPN transistors
(1) 78L33 3.3V 0.1A voltage regulator
(1) 0.1uF 10V capacitor
(-) hookup wire, 300V
(24”) hookup wire, 26ga, low voltage
(1) PCB or hand-wired board, 0.82" by 2.34"

part list, indicator
(1) X-10 appliance module
(1) Incandescent light bulb style night light, manually controlled (not an automatic sensor type).