💡 Squarely

A super low-frequency square wave counter originally built back in high school, designed for basic signal counting and hands-on hardware experimentation. It uses classic 74-series logic to drive a multi-digit display and can be expanded or tuned for various applications.

Reflecting on the original design, here are a few areas worth improving:

• Replace discrete resistors with a resistor bank — cleaner layout and easier substitutions
• Adjust the 555 timer's RC values to support higher input frequencies (up to low MHz)
• Add a third digit to extend the count range
• Use logic chips from the same family (e.g., 74HCXX) for consistent behavior and performance
• Pull unused inputs high or low to prevent erratic logic states
• Support an external clock input via pin 14 (CP0) of the first 74XX90 counter for easier integration or testing

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🔹 Rev 1 Schematic

🔹 Rev 1

• Tracking versions.

🔹 General Notes

• Input Signal Options:

  • Internal 555 timer (adjustable via RC timing)
  • External square wave source (connect to pin 14 / CP0 of the first 74XX90)

• Display:

  • 2-digit 7-segment display (expandable)
  • Driven by chained 74XX90 decade counters and 74XX47 BCD-to-7-segment drivers
  • A D flip-flop latches the output from the counters to the display drivers

• Modularity:

  • RC timing is easily adjustable for frequency testing
  • Logic chips can be swapped to experiment with propagation delays, power consumption, or chip families