24 Hour Digital Clock (non Microcontroller)

This is a simple 24 hour digital clock using CMOS ICs, no microcontroller used, and this keeps really good time.

I am going to provide the schematics for this and a few photos of the solderable breadboard I used. This is also a 2 part instruction, as you can just make the clock and you can also make a battery backup, link provided below, that will allow brief interruptions in power without having to set the time again.

For this you will need a basic understanding of reading schematics, soldering or breadboarding (depending on which way you want to go with this), and using a multimeter. This would be a great learning project for a school that has this type of instruction.

This is NOT my creation, I am simply sharing it here for people to use. Full credit goes to Dan, danyk.cz for this brilliant design. Photos however are my own, and I have made this on a breadboard as well as a solderable breadboard.

For the battery backup: instructables.com/Battery-Backup/

The parts list is for a solderable dual breadboard:

 7 segment LED display, .56”, 5161AS, common cathode, x6

CD4026BE decade counter, x7

CD4060BE binary counter, x1

1N4007 diode, x2

1N4148 diode, x9

100K resistor, x3

10M resistor, x1

470K resistor, x1

10K resistor, x2

1K resistor, x1

22 pF disc capacitor (symbol is 22), x2

.1 uF disc capacitor (symbol is 104), x8

1 nF disc capacitor (symbol is 102), x1

32.768 kHz oscillator, x1

tactile switch, x2

16 pin socket, x8

Header pin, x2, I use a red and a black

5 volt DC power supply

Optional, a test point ring, black bead

22 AWG solid wire, colors as needed, I use red for +5, black for ground (standard), a color for the clock generation section, and another color for data to the LED displays.

Solderable dual breadboard, x1. I am in Thailand so I use a local made PCB, and here is the Mouser part # SB1660 for a similar board that looks quite good.

Soldering iron, solder, isopropyl alcohol, desoldering braid and liquid flux as needed. Multimeter for testing.

If you want to make this on breadboards, you will need 2 full size breadboards. I have made both and will show those. The solderable breadboard will go into a frame shortly and I will add that photo after that has been completed.

If just using breadboards, omit the DIP sockets and the .1 uF caps, just use a 10 uF electrolyte cap between the buses.

This is the type of solderable dual breadboard I have available here and you can see it compared to a standard full size breadboard.

Mouser Electronics carries a solderable dual breadboard as well that looks quite good as well, Mouser part # SB1660.

If you want to build this clock using standard breadboards, you will need 2 full size boards. Remove the bus strip from 1 board and join the two boards together. Note the orientation of the bus strips, the + bus is above the - bus and you can layout the parts exactly like the photos.

First thing you need to do is place 7 sockets on the lower board section and 7 segment LEDs and 1 socket on the upper board section. Connect the buses and install the tactile switches.

Then add the diodes at the top left and the ground wires to pin 8 of each LED, note that these are NOT to the ground bus, these are connected to the anode of D11 as per page 4 of the schematic. And add the power and ground wires for the sockets.

Now add the decoupling caps and the caps used for the clock circuit. And add the resistors that will be used in the diode resistor AND gates. Add the wires for the clock circuit, I used green, on the bottom row of DIP sockets.

I got carried away and did not take step by step photos for this, but it is straight forward.

First, complete the clock circuit by adding the resistors, oscillator, and wiring, I used green.

Add the data wires, I used white. Then add the header pins and optionally, add a test point ring on a ground bus.

Before powering this up, and good practice as you are assembling this, using a multimeter, check resistance between power and ground buses to identify any shorts. Visually inspect all solder connections to make sure there is no bridges between pins.

Connect power to the header pins and all the LEDs should read 00 00 00 with the seconds counting.

Watch the seconds count from 00 to 59 and it should switch to 00 and will repeat. You are verifying each digit, if a segment of a digit is missing, then you have 2 pins bridged and you need to inspect the solder joints on the pins again.

Now using the minutes button (lower button), press and hold that and watch the minutes to verify the correct segments light for 00 to 59 then to 00. Again, if some segments are missing, you need to inspect the solder joints.

Now using the hours button (upper button), press and hold that and watch the hours to verify the correct segments light from 00 to 23 then to 00. If missing any segments, you should know what to do now.

Now set the correct time. Check it in 1 day and it should be perfect. Enjoy your clock.

Place the DIPs, LEDs, and tactile switches as shown.

Add the diodes, wires to connect the buses, ground wires to the LEDs, ground and power wires to the DIPs, and the clock wires to the bottom row of DIPs.

Add the resistors, capacitors, oscillator, and wires to the clock circuit. Note the electrolytic capacitor and a few disk capacitors on the bus, simply added to reduce noise on the bus. Some data lines added as well in yellow.

Add the rest of the data lines (yellow), resistors and diodes for the AND gates, and power it up. Check for missing segments in the digits and the troubleshooting is making sure good contact with the wires. Enjoy.