How do you blink a light with only discrete components? The Astable Multivibrator, which is a type of relaxation oscillator. ‘Astable’, meaning it’s keeps flipping between two states, and never rests in one (we’ll see this later when exploring the venerable 555).
We’ll draw this up in a moment, but first lets pick a flashing rate, and see how close we can get.
And again, I’m exploring and winging it in real-time, so I’m going to be wrong, but: The time constant is simply R*C, which gets us to 63% of the total charge of the capacitor in the RC circuit. Will this circuit flip at that point? I don’t know! But lets use it as a starting point.
Lets try for a period of 1 second. I’m going to guess that we need a pretty large value of C, and I’m going to pick a standard value, say 47uF. So now we have to calculate the R, given T & C:
R = T/C == 1/47e-6 (sorry, that’s horribly formatted scientific notation) = 21,276, or ~22k, which is super convenient, since that’s a standard value as well (huge coincidence, or exactly how the grandfathers of electronics intended?)
Fun fact: The Astable Multvibrator is the only schematic that it’s OK to use diagonal lines for!
When wired up, it has a nice symmetry, which is super important in the field of electronics.
And you’re not gonna believe this, but it worked on the first time. I’m calling that pretty damn close to 1 second period too… so yeah, Day one’s in the bag 🤘.
Video’s on the second pic.