clock module

2 Articles

Clock Mechanism Goes Crazy For Arduino

March 9, 2025 by 28 Comments

You’ve doubtless seen those ubiquitous clock modules, especially when setting clocks for daylight savings time. You know the ones: a single AA battery, a wheel to set the time, and two or three hands to show the time. They are cheap and work well enough. But [Playful Technology] wanted to control the hands with an Arduino directly and, in the process, he shows us how these modules work.

If you’ve never studied the inside of these clock modules, you may be surprised about how they actually work. A crystal oscillator pulses a relatively large electromagnet. A small plastic gear has a magnetic ring and sits near the electromagnet.

Each time the polarity of the electromagnet flips, the ring turns 180 degrees to face the opposite magnetic pole to the electromagnet. This turns the attached gear which is meshed with other gears to divide the rotation rate down to once per 24 hours, once per hour, and once per minute. Pretty clever.

That makes it easy to control the hands. You simply detach the electromagnet from the rest of the circuit and control it yourself. The module he used had a mechanical limitation that prevents the hands from moving well at more than about 100 times normal speed.

We wondered how he made the hands reverse and, apparently, there is a way to get the drive gear to move in reverse, but it isn’t always reliable. Of course, you could also replace the drive mechanism with something like an RC servo or other motor and it sounds like he has done this and plans to show it off in another video.

We’ve seen the opposite trick before, too. If you really want an easy-to-control analog clock, try this one Continue reading “Clock Mechanism Goes Crazy For Arduino” →

A New Battery For A Potted Clock Module

August 6, 2017 by 31 Comments

If you did much dismantling of PCs back in the 1980s and 1990s, you might be familiar with the Dallas Semiconductor range of potted real-time clock modules. These were chunky dual-in-line devices containing clock and non-volatile RAM chips, a crystal, and a lithium battery. The battery was good for about a decade, which was fine for most PCs of the day because the majority of desktop computers are replaced long before that deadline.

[Glitch], however has an industrial single-board computer with a 486 processor that has had a life much more prolonged than its desktop siblings due to its application. The battery in the onboard Dallas DS1387 has long ago expired, and since these devices are so long out of production to be unavailable, he’s had to improvise.

Improving on some previous documented projects he found through an internet search, he carefully ground away the potting compound to reveal a couple of the battery conductors, cut them with a PCB drill, and mounted a lithium cell holder on the top of the device with some tidily soldered Kynar wires to bring in the power. A CR1225 cell was used rather than the ubiquitous CR2032, as space was at a premium in the width of the ISA card form factor.

The potted RTC module is something of a rare device these days, but if you have a retro computer containing one this seems to be a very useful piece of work to bring it back to life. We’ve covered another similar one with a slightly larger battery in the past.