2nd digit and RTC

A project log for Relay Logic Clock

A digital 24 hour clock using only relays and diodes for the counting logic.

Dave GönnerDave Gönner 01/11/2016 at 12:500 Comments

Today I finished the decoder for the 2nd digit. The minute display section is now complete. As you can see in the video, I finished a prototype of the battery powered real time clock as well. When the power is applied, the clock shows "10" minutes, this is because the 2nd display is clocked by the first display when it shows 0. So on power up the 2nd display immediately gets a clock and increments.

Connected to the relay clock you see an Arduino with a real time clock. I use a Maxim DS1307 to keep the time. It is connected via I2C to the processor. I have a temperature compensated crystal oscillator, a Maxim DS32KHZ, which is supposed to be accurate to +/- 2 PPM per year. This is only a prototype, in the end I will design a small rectangular board that will go in the free position at bottom of the outer circle.

After the processor powers up, it reads the time in the RTC and then sends out clock pulses tot the relays until the time on the displays corresponds to the time in the RTC. The two buttons can be used to increment the hours or the minutes. On incrementing the minutes, the seconds in the RTC are reset to zero as well.

The clock is now half done! On to the hour section. This will require some more relay trickery to get the thing to roll over from 23 to 00. I have yet to design the decoders for this, so I hope it will all fit on the available board space.