Hi all,
I recently added a 0.01uf capacitor across one of my ICs ("decoupling"). Thanks for the advice guys.
It works great at supressing electronic noise, but I don't understand HOW. It would seem to me that connecting the positive right to the negative would shut the whole thing down. But obviously it didn't. So what does a capacitor's uF value mean?
How much current is allowed to pass through it?
Or how much current it stores at any given time?
Caps are great, though I
Caps are great, though I don’t completely understand how it works, just the basic understanding. Best way I can explain it is that it’s a resovoir that has extra room for the high spikes. when you get the high spike it flows a little faster. when it dips, it flows a littls slower, but keeps it at a relativly constant stream.
I’ve seen it in action when I hooked a 1k uf cap to a solar panel that was connected to an led. It just happened that their was a tree branch that started blocking the light and it was a bit windy, so since it was moving it would dim and brighten at a smooth rate. When I took out the cap it was noticable as the amount of light directly affected the current going to the led.
Too many analogies - a love story
The capacitor can be explained in many different ways. The “cap” has also many different uses. When used as a spike suppressor, consider the cap to be a flood valve.
Only sudden bursts in the voltage will be shorted. The DC voltage will be blocked. How long and high a burst will be suppressed is depending on the capacitor’s “capacitance” or capacity. Capacitance © is the official, nerdier word. The unit for this is the Farad (after Faraday). One Farad is a ■■■■■■■■ of C. That’s why we use much smaller units. Like a millionth (micro, uF) or a billionth (pico, pF) of a Farad. Smaller even sometimes.
Inside the cap, the leads are not “touching” each other. That’s why it will not conduct a decent current. Instead, it has two surfaces very close to each other, all wrapped up in a very tight package. Even tough the electrons cannot travel across from one surface to the other (they are separated by an insulator), they sure can “feel” each other’s presence on either side of this barrier.
Very psychic they are, these electrons. The larger the surface area, the more room there is for extra electrons to settle in and have a pick nick in each other’s company albeit separated. Very Romeo and Juliet. For some reason these electrons are only attracted to the ones they cannot have. All Romeos one one side and all Juliets on the other. And not a gay one among them.
It’s the different “electrical potentials” on either side of the cap that makes the difference (between boys and girls). Such a difference is what we call “voltage” in every day robot building. The higher the difference, the more passionate the lovers. When a sudden electrical burst (motor noises) brings that voltage up, more electrons on either side go into the capacitor. They have a bigger urge to do so. When the peak subsides, electrons will return to their daily routines. But in the mean time, a massive over voltage has been averted in your motor driver.
From outside the cap, it just looks like electrons went into the cap when there were “too many” around. This analogy is false and the first proper electrical engineer to read this will most likely scold me for it. But from the perspective of an average robot hobbyist, that’s why you want a capacitor across your motor leads.
BTW, this story has a happy ending. The Romeos and Juliets will get each other in the end. Just not inside the capacitor.
Caps block DC but allow AC
Caps block DC but allow AC to pass through. They have two plates internally that do not touch (very important). With no connection between them you can see why DC would be blocked. With an AC signal one plate is “charged up” and the charge is “induced” upon the other plate like between the coils of a transformer, seemingly allowing it to pass through. It doesn’t really but you can think of it that way.
edit: oops, sorry Rik you beat me to it. and did a better job too I might add.
lol
"Very psychic they are, these electrons …"
Funny enough to get me actually writing LOL. Thx for th’info guys.
dude I do not want to
dude I do not want to confuse you,just a simple description:
capacitor is sensitive to changes
when the voltage across capacitor changes .it acts like it passes the voltage signal.the higher the frequency,the better capacitor passes the signal(changes).
it is like a resistor wich is controlled by frequency.
if you increase the frequency the resistance in front of signal DECREASE.
noise has high frequency.
so capacitor passes the noise through itself.
if one of the legs is grounded,so it simply passes the noise to ground
