### Author Topic: Large Black capacitor confusion  (Read 1741 times)

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#### kurtron9000

• Beginner
• Posts: 5
##### Large Black capacitor confusion
« on: May 20, 2008, 11:50:07 PM »
I am using The battery holder and the 9 volt battery duo.  I was reading back and forth and towards the beginning of step 3b it says not to connect the + end of the capacitor to the voltage regulator. Then it says not to connect it to the servo bus.  I understood that its purpose was to continue to power to electronics in case of problems so i logically decided it would only make sense to connect to + end of the Capacitor to the unregulated input of the voltage regulator.  So if your following my thought process to this point you would understand if I would do a dandy little verification check.  All the voltages check good until I unplug the 9 volter and attempt to discharge the rest of the voltage.  This is where my next problem is. The multimeter reads zero everytime.  Unless my electronic principles are a little weak, which is probable, I should be getting declining voltage readings!!! If this makes any sense please help me!!! If not I'd be happy to clarify, I'm so close!!!

#### bukowski

• Robot Overlord
• Posts: 219
##### Re: Large Black capacitor confusion
« Reply #1 on: May 21, 2008, 10:57:16 AM »
As I understand it, the cap is a filter used to "level out", or reduce ripple, to the input voltage to the regulator. Otherwise this noise could be transmitted to the output. The capacitor doesnt really charge that much because it is in parallel with the circuit.

#### kurtron9000

• Beginner
• Posts: 5
##### Re: Large Black capacitor confusion
« Reply #2 on: May 21, 2008, 08:26:47 PM »
Alright thanks, that would make sense.  Just to double check when using the battery holder and the 9 volt batt. the + side of the CAP goes to the +(unregulated input) pin on the voltage regulator?

#### SixRingz

• Full Member
• Posts: 76
• Bit's and pc's = Robot.
##### Re: Large Black capacitor confusion
« Reply #3 on: May 22, 2008, 09:41:37 AM »

http://www.seattlerobotics.org/encoder/jun97/basics.html

Quote
All the voltages check good until I unplug the 9 volter and attempt to discharge the rest of the voltage.  This is where my next problem is. The multimeter reads zero everytime.  Unless my electronic principles are a little weak, which is probable, I should be getting declining voltage readings!!! If this makes any sense please help me!!! If not I'd be happy to clarify, I'm so close!!!

Well, my electronic skills aren't what they used to be but I would say that it may be that your capacitor discharges so quickly that you don't have time to measure it. (I'm talking milliseconds or less) All this depends on the RC-circuit configuration. Unless you are ninja-fast with the multimeter....
Grounding things properly means burying them in the backyard...

#### Webbot

• Expert Roboticist
• Supreme Robot
• Posts: 2,166
##### Re: Large Black capacitor confusion
« Reply #4 on: May 23, 2008, 05:59:34 PM »
Check out my attached file at  http://www.societyofrobots.com/robotforum/index.php?topic=3292.msg25198#msg25198 This shows the cap going between the supply rails of the servo motor supplies.
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• Robot Overlord
• Posts: 293
##### Re: Large Black capacitor confusion
« Reply #5 on: May 24, 2008, 12:40:58 AM »
After reading this thread I believe people here need some basic introduction to electronics an robotics with capacitors.

Capacitors have two functions:
DC circuit function: charge up and then realease a high current(like in camera flashes). However this fuction is not that popular in robotics. In this case the current dont flow trough the capacitors.

AC circuit function: in AC circuits the capacitor becomes a resistor. Its impedance(the resistance) is calculated as Z=1/(jwC), where j is the imaginary unit, w=2*pi*f where f is the frequency of the current and C the Capacitance. In other words, the higher the frequency of the AC, the lower will be the resistance of the capacitor. This function is widely used in electronic cicuits of any kind to remove noise(except, maybe, pure logical cicuits). Those are band pass filters. If it is a low band pass circuit the circuit will allow AC with low frequency to have high gain output. High bang pass filters are the opposite. You can also combine those two filters and have a hybrid filter. In this case current flows through the capacitors.

There is also  a AC-DC cicuit function. This is used in biased transistor circuits. But that is just a mixture of the two functions above.

Once you know that you can understand why put capacitors between the pins of the regulators. They filter the noise that might damage your ICs. That is why it is also recommended to put some capacitors in parallel with DC motors. AND that is the reason you shouldnt NEVER, EVER, put a capacitor neighter in series nor in parallel between the PWM output of your microcontroller and the servo signal input socket/pin. The PWM signal is basicaly squareshaped AC. It has a frequency therefore the capacitor will react to it in the same way it will react to noise: the PWM signal will be filtered and your servo wont work.

Finally, about the "direction" you have to solder the capacitor. Capacitors are generally divided in two kinds: ceramic capacitors and electrolytic capacitors. Ceramic capacitors are the same ones you learn about in school: they are like resistors and can be soldered in any "direction". On the other hand there are the Electrolytic capacitors that have a direction. The capacitor you are using is Electrolitic if you connect the + side in the ground(which can also be considered the - side) your capacitor will just explode. Because of that you MUST connect the + with the + and the - with the -. (in a more precise way, you connect the + side of the capacitor with the highest electrical potential terminal and the - side with the smallest electrical potential terminal.)

The tutorials and above links are good but they more like cake recipes.(SOMETIMES)  They dont teach you the reasons behind the instructions. So if want to experiment you are (SOMETIMES) ****ed(unless you study, of course).
A.I.(yes those are my initials)