A simple precision clock, with LCD display. The clock uses an inexpensive precision reference
for accuracy of a few seconds per year.
Ever wanted a clock that would keep really good time, even during power cuts? Ever wanted a clock with the bells and whistles YOU wanted? This little project keeps very good time, and has battery backup, so it keeps going (and telling the time) through power failures. It also features serial time output and a built-in phase detector system for self-calibration. There are resources to spare for additional features to be added.
The project utilizes some interesting concepts in time keeping and frequency precision, and makes maximum use of recycled components. The Superclock makes a great platform for learning about time and frequency.
This project has now been 'retired'; however it can still be constructed with full functionality, using the GPSClock design with a few simplifications.
To build the Superclock with the GPSClock design, you:
- Replace the voltage controlled reference (VTXO or OCXO) with a suitable cheap TCXO
- Ignore and omit the PWM feedback components
- Use exactly the same firmware and PC software
The clock is quite inexpensive to build - two ICs and a couple of transistors. One of the ICs is an AVR microcontroller - also inexpensive, and quite powerful. The other is a simple three-terminal regulator. The LCD display is a standard type used everywhere, and could be recycled from a broken business phone or appliance. Precision time keeping is achieved through the use of a Temperature Compensated Crystal Oscillator (TCXO), which could be recycled from an old cellular phone. Just about any frequency from 9 to 15 MHz can be used. Some of the features of the unit are:
The serial data can be used for time logging, or setting other clocks. The phase information can be used for calibration or long-term tracking of the reference oscillator error.
- Dual time operation, UTC (Greenwich) time and local time
- Any whole hour time zone, including summer time (daylight saving)
- UTC display in hours, minutes and seconds, settable to within milliseconds of UTC
- Local time in 12 hour format, am or pm. Local time offset shown on screen
- Local time offset adjustable for daylight saving without affecting clock time
- Time setting via computer - no buttons or knobs for kids to fiddle with!
- Built-in calibration via phase detector, for 1 part in 107 accuracy or better
- Serial data time message every second, including phase
- Simple fully documented bi-directional communications protocol
- Precise 5V level 1 kHz and 1pps outputs, hourly chime output
- BATT indicator on display and chime warns of main power failure
If super accuracy isn't important to you, you could also replace the TCXO with a simple crystal, trimmed to frequency using the calibration procedure provided in the software.
For more information, see the GPSClock project.