Basic Circuits of a Computer

Date
3 October 2025	Assigned
10 October 2025	Due
Fundamental
Hack

Introduction

As we extend our understanding of circuits, we see that we can build real things that have real functions. This assignment asks you to build a digital padlock which can:

• store a three-bit combination
• allow a programmer to "hide" this three-bit combination to secure the circuit
• evaluate input of a three-bit combination
• notify the user that entered combination matches the programmed combination, when true
  • if and only if true, an "unlock" light should latch high

Here is a crude block diagram demonstrating the circuit:

• 1 74LS86 (XOR)
• 2 74HC02 (NOR)
• 2 74HC04 (NOT)
• 3 74HC08 (AND)
• 2 4-input DIP switches
• 2 830-pin breadboards
• 1 LED (for final circuit)
  • To test the circuit,you're allowed 5 total LEDs
• as many transistors as desired

Finishing this circuit will require the correct application of circuits we've learned this week as well as incorporating logic similar to the Equality Comparator (an earlier Hack).

Instructions

You must complete and demonstrate this circuit to an instructor or TL using your breadboard and associated parts. This can be done any time during the duration of the assignment until the due date.

In addition, you must record your findings in the report.md file in the docs/ directory. This documentation will require you to fill in some truth tables, provide some breadboard layouts, and explain how each of the circuits work, ostensibly. The report also contains a table for the instructor or TL to fill out when circuits are demonstrated. Again, this table must be filled out by the instructor or a course TL. (This means that you'll have to have commits authored by one of these folks!)

Assignment "Hack"

Note: to complete this hack:

• you will need to request permission to use up to two (2) additional chipsl
  • request these of the instructor or a TL and document them in the Hack's report.md.
• Hackers are also permitted an additional switch in order to incorporate the Enable function of the involved circuit(s).

How much work does it take to turn this into a 4 bit combination lock? Do this hack, and you'll find out.