Just for fun, I want to start today's email by confusing you.
So here is what I think is the absolutely worst way to explain a capacitor to a beginner (and this was actually copy-pasted from a well-known source):
"A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field."
While this is a true statement, it's a pretty useless description to use when you want to teach someone electronics.
And there are actually a lot of electronics books that are written in this way...
So, this is the way I like to explain the capacitor:
"A capacitor is kinda like a tiny rechargeable battery with very very very low capacity. Instead of lasting for a few hours, like a normal battery, it lasts only a couple of seconds - or sometimes much less."
I like this explanation because it is so much easier to relate to.
But it's even better when you can see it for yourself.
In the following video, I've connected a capacitor to the simple LED-circuit from the first email.
Pay attention to what happens when I disconnect the battery:
https://youtu.be/CVywtFTEz3I
Did you see it?
When I disconnect the battery, the LED stays lit for a few seconds, then fades out.
That's because of the capacitor.
It takes a bit of time to charge a capacitor. And it takes a bit of time to discharge a capacitor. You can use this to create a time delay.
Two things to keep in mind before you look at the next diagram:
- A capacitor is always discharged in the opposite direction of how it was charged
- No current flows into the input of the inverter
So, here's where the capacitor will fit into the circuit you and I are building:
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There's also an extra resistor as you can see.
With the capacitor connected to the input, the input can't change instantly.
To go from LOW to HIGH, we need to charge the capacitor.
To go from HIGH to LOW, we need to discharge the capacitor.
The added resistor reduces the current to/from the capacitor so that it doesn't charge and discharge too fast. So when you connect a resistor and capacitor in this way, you create a 'delay element'.
The voltage you have on the left side of the new resistor will, after a short delay, also become the voltage you have on the right side of the resistor.
The size of the capacitor and the resistor decides the time of the delay.
Our new circuit works like the circuit in the previous lesson, only that when you flip the switch, there will be a delay before the LED turns on or off.
If you're extra curious and want to understand how the current flows in this circuit, check out my notes on this here:
https://build-electronic-circuits.com/lesson4-notes
If you're scratching your head a little at the circuit diagrams - don't worry! I understand.
For people new to proper circuitry some of the notation and diagrams take a little getting used to.
The good news?
It makes sense in its own sweet time and once it does... well, you wonder how you could ever have not understood it! It's like when you finally stopped falling off your bicycle.
Give it some time, and these things really do become second nature.
In the next email, we'll look a little more closely at how the capacitor, the resistor, and the inverter combine to make the LED flash on and off.
And everything is going to make sense...
Then let's see if we can make the light blink!
SUMMARY
You met the capacitor - a component that stores up some charge before discharging it into the circuit. You also saw first-hand how a delay element delays a voltage. And you realize that these diagrams will make more sense the more of them you see!
Keep On Soldering!
Oyvind @ build-electronic-circuits.com
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