Getting the power supply right is the hardest part of any electronics project. You have to get it stable before you worry about anything else. The rest of the clock is just logic. But logic needs power.
The schematic for the power supply and time base is your starting point. Once that’s solid, you can build the rest.
To make this work you need specific parts. Not all of them. But enough to get seconds working.
Here is what you need:
- At least four 7490 or 74LS90 chips. These are counter ICs. They count the pulses.
- At least two 7447 or 74LS47 binary-to-7-segment converters. They turn binary numbers into digits you can read.
- At least 20 resistors for the LEDs in the 7-segment displays. 330 ohms is fine.
- Some normal LEDs. Just for testing or extra indicators.
- At least two common-anode (CA) 7-segment LED displays. Jameco part # 17208 is typical. You can find alternatives.
- Breadboards and wire. See a complete list elsewhere if you need more.
The number of chips depends on how many digits you want. This guide only covers seconds. So the “at least” numbers are correct. If you want minutes you need more. But for seconds the list above is enough.
Start with the power supply. Get it working. Then add the chips. One by one.
