EvaUnit02's Creations

I'm working on building a breadboard general-purpose computer as an exercise in learning electronics.

All computers begin with a timer. So, this is my Texas Instruments LM555CN timer with a potentiometer to control the timing rate.

Astable 555 Timer

Here's the circuit diagram.

Astable timer circuit diagram — Astable timing circuit diagram.

I will also want to be able to step through instructions being executed; so, I have a second, monostable, 555 timer with a button to activate a clock tick.

Monostable 555 timer

Here's the circuit diagram.

Monostable timer circuit diagram — Monostable timing circuit diagram.

In order to switch between the two timers, I have a third, bistable, 555 timer where I'm leveraging its flip-flop as a debounce circuit for a switch. This will ultimately connect the previous two timers and switch between them.

Bistable 555 timer

Here's the circuit diagram.

Bistable timer circuit diagram — Bistable timing circuit diagram.

Finally, I used three more TI packages for logic gates to hook it all up. The SN74LS04 is a package of inverters. The SN74LS08 is a package of AND gates. The SN74LS32 is a package of OR gates.

Now, the switch on the bistable circuit will switch between the astable clock and the monostable clock. So, I can run the computer like normal (astable) or step through code (monostable). There's also a halt line that will stop the clock altogether.

Completed clock

Here's the circuit diagram.

I've also modified my primary arcade stick with new components including two control boards. Here are the galleries of those modifications.