I wanted a Hawkeye/EagleEye indoor/outdoor X10 movement sensor (MS14A) for a while, but the prices on UK eBay were around £30 each. This was around 2010. When I saw a deal in America—$30 for a 6-pack—I jumped at the opportunity. However, I soon discovered that these sensors operate at 310 MHz, which isn’t compatible with European X10 frequency standards.

I suspected that a conversion to 433.97 MHz might be possible, even though my initial online search didn’t yield any obvious guides. I started by examining the RF section of the circuit and redrawing the schematic. My first step was to check if the transistor (KSP10) could operate at 434 MHz. Fortunately, its specifications allow operation up to 650 MHz.

The frequency of these sensors is largely determined by a tank circuit. This is a capacitor and wire loop in parallel on the PCB. The tuned coil whose length sets the oscillator’s frequency. A shorter coil produces a higher frequency. In my sensor, the original loop was quite large:

I carefully cut and shortened the loop. After much trial and error, I finally achieved the target frequency of 434 MHz, as shown in the photos below.

To replicate this conversion, you’ll need a frequency counter or a receiver tuned to around 434 MHz with a signal strength indicator, so you can precisely adjust the tuned coil. Keep in mind that modifying and operating the sensor at either frequency may violate local regulations in the UK/Europe.

As illustrated in the photos, I drilled a new location for the wire link and re-soldered it. Adjusting the position of this link—ideally using a plastic tool to avoid interference from your fingers—allows for fine-tuning of the frequency. The circuit is very sensitive and requires patience to achive 434 MHz.

Note: Changing the way RF equipment transmits is against the law in Europe. This modification is strictly experimental and should only be performed in a controlled, closed environment.

 

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