DIY RX8025 Clock Mod with AAA Batteries

If you're interested in DIY clock crystal oscillator mods—specifically the RX8025—this article is worth a look.

Before diving into the mod, you'll need an old LED clock with outer dimensions of about 21 x 14 cm and a screen size around 17 x 9.5 cm. The clock should be capable of displaying time, weekday, date, and temperature. Once you’ve got one, take it apart. These kinds of clocks are usually quite simple inside—typically just a single circuit board and a speaker.

So, how do you go about modifying the crystal oscillator? It's pretty straightforward: remove the original oscillator and 22pF capacitor, then connect three wires to where they were. That's it. If you're aiming for better power efficiency, though, there's more to consider. For example, avoid using CR2032 coin cell batteries—they drain quickly, often needing replacement in less than two months. If possible, convert any LED clock using coin cells to run on AAA batteries instead.

If your clock—like the one used in this example—originally runs on three AAA batteries, you'll find a hidden bonus when you take it apart: the internal circuit board and back panel actually have support for 5V DC input. It was likely removed from the final product to save on costs. The current setup uses a diode to drop the voltage from the three AAA batteries, followed by a 3V regulator to power the circuit.

Once you've installed the RX8025, the current draw with three AAA batteries will be about 0.25mA. If you don't need the hourly chime, simply cut the speaker wire to save even more power. Alternatively, you can run the clock on just two AAA batteries without using an LDO regulator—it'll still work. Just be sure to add a 1N4148 diode in series to prevent the voltage from going over 3V, which could otherwise cause the display to darken and show unwanted artifacts. In testing, the voltage measured around 2.2V, which is still sufficient for operation—though the display may appear a bit dim. The upside? Power consumption drops to under 0.1mA, meaning two alkaline batteries could easily last a year.

Done.