In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Peter Van der Zee wrote:

Hi ACE 227;

You might be misdirected by the above post...... with a little inginuity, you can very well create a complete real time clock with a multiplexed display from a single SX 28 chip.

No external driver chips of any sort are required.... just the SX, 4 Seven segment Digits, 8 leds for the 10 Seconds and Seconds, and 8 resistors. Depending on the brightness you desire, an additional 12 resistors may be required.

You would also want to include two momentary push buttons for setting the time. I use a dimming technique to indicate which digit is being adjusted for time, and the two buttons to Raise/Lower the time value for that digit. Pressing both buttons momentarily advances the adjustment to the next digit. When adjusting the time, the speed of the Raise/Lower interval even changes.

For stability, the oscillator source should be a standard crystal, probably in the 4 Mhz range.

I have created hundreds of multiplexed displays as well as discrete multiplexed LED drivers with just this approach, and the results have been excellent.

Cheers,

Peter (pjv)

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