Day 2 of my 8bit Breadboard Computer Build!
today, I assembled and tested the monostable 555 timer circuit, which serves as the manual clock pulse generator, allowing me to advance the CPU one step at a time, unlike the astable mode I built on day 1 (which continuously oscillates), the monostable mode produces a single pulse each time it’s triggered, this pulse acts as a single “tick” of the computer’s clock, letting me observe each instruction or logic operation manually, an essential feature when debugging the early stages of a CPU, here’s how it works fundamentally: when the trigger pin (pin 2) receives a low pulse, it causes the output (pin 3) to go high for a fixed duration, determined by the resistor (R) and capacitor (C) connected to pins 6 and 7, the timing period is calculated using the formula:
T = 1.1 × R × C
during this time, the capacitor charges through the resistor until it reaches 2/3 of the supply voltage, at which point the internal comparator resets the flipflop and brings the output low again, to ensure stable operation, I used a debounced push button for the trigger, along with decoupling capacitors across the power lines to suppress noise and prevent false triggering, the output LED visually represents the clock pulse width, lighting up each time the circuit is triggered, with this, I now have both modes of clock control:
Astable Clock → Continuous automatic clock.
Monostable Clock → Manual singlestep control.
this gives me full control over the timing of my computer, allowing precise debugging as I move toward building the registers and ALU next.