Like many electronics hobbyists, [Pete] found that he had an overwhelming desire to build a clock for himself. He didn’t want to stick a discrete real time clock IC into a box and call it a day, so he opted to construct his own around a microcontroller instead.

After researching the specs on a few RTC ICs, he defined some accuracy requirements for his clock, and got to building. He started out using a 32,768 Hz watch crystal, but found that the accuracy was off by about 46 ppm after only 24 hours of use. That fell well beyond his self-imposed +/- 3 ppm tolerance goal, so he purchased an oscillator with about 500 times the resolution of his previous crystal.

After writing a handful of code to ensure that the clock remains stable, he calculated that his accuracy should be about 0.18 ppm – well within his acceptable tolerance range.

[Pete] says that this is just the first part of his clock construction, and that future revisions should include plenty of additional functionality, so keep an eye out for updates.

[Audin] got a hold of a pressure gauge and decided to turn it into a clock. We were under the impression that these types of gauges were filled with oil but he didn’t detail cleaning it up for his purposes. Once he gained access to the guts he replaced them with a stepper motor. The motor connects to an Arduino with the help of a Darlington array for handling the large load. [Audin's] plans include using a real time clock (on order) and moving to an AVR ATmega8 microprocessor once the prototyping is finished. In the mean time, he has posted the code used in his current prototype.

Stay with us past the page break for some video of this in action. He’s got the needle dialed in for very precise movement and has coded a “jitter” effect as well. We’re not sure this would be the most convenient clock, but we’d love to affix it to our kitchen stove for a gnarly looking timer. [Audin] acquired the gauge at his local Habitat for Humanity ReStore, a place we’ve used many times to source reclaimed and unused items of all kinds for our projects.

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The PCF8563 is a real-time clock/calendar/alarm chip with an I2C interface. This would be useful in projects where the primary microcontroller doesn’t have enough resources for an interrupt driven clock.

We demonstrate the PCF8563 using the Bus Pirate after the break. For a limited time you can get your own Bus Pirate, fully assembled and shipped worldwide, for only $30.

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