Author Topic: newby question about capacitors  (Read 1308 times)

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Offline schoebyTopic starter

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newby question about capacitors
« on: November 14, 2011, 04:56:32 PM »
I am another one to try the $50 robot.  Long time programmer first time this close to hardware.  Anyhow, I have been following the  simpler "schematic" provided in  the post "$50 Robot with AVR ISP mkII 6 pin" with a visual representation of the solder points.  It turns out i am not bad at soldering.  I only blew out one terminal by overheating it with my iron set too high!  The next one will look much better.

Anyhow, my question is what is the purpose of the capacitor located between L18 and L20?  It appears(to me) that it only offers anything to the 6 pin programmer pin 2 since it is after the two connections on the controller.  This is based on "BASIC ELECTRONICS COMPONENTS TUTORIAL FOR ROBOTS" description from this site.  However, maybe it is because of the mention that electrons flow from ground to source?  Based on that description the capacitor between D11 and E11 makes sense to me.

Thank you for the info!

Offline voyager2

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Re: newby question about capacitors
« Reply #1 on: November 14, 2011, 07:55:01 PM »
Hi,

I am another one to try the $50 robot.  Long time programmer first time this close to hardware.  Anyhow, I have been following the  simpler "schematic" provided in  the post "$50 Robot with AVR ISP mkII 6 pin" with a visual representation of the solder points.  It turns out i am not bad at soldering.  I only blew out one terminal by overheating it with my iron set too high!  The next one will look much better.

Anyhow, my question is what is the purpose of the capacitor located between L18 and L20?  It appears(to me) that it only offers anything to the 6 pin programmer pin 2 since it is after the two connections on the controller.  This is based on "BASIC ELECTRONICS COMPONENTS TUTORIAL FOR ROBOTS" description from this site.  However, maybe it is because of the mention that electrons flow from ground to source?  Based on that description the capacitor between D11 and E11 makes sense to me.

Thank you for the info!

From what I've seen the Ceramic Cap is for the Analog to Digital Converter inside the MCU.

Quoting from the tutorial
http://www.societyofrobots.com/step_by_step_robot_step3A.shtml
Near the bottom of the page:


Quote
A second 0.1uF capacitor must go between GND and AVCC, as close to the microcontroller pins as you can make it. This capacitor is required to create a low pass filter for the analog-to-digital (ADC) converter.

If you ever do high precision ADC measurements (unlikely), put a 0.1 uF cap in between AREF and ground as well. The point behind having the AREF pin is so you can feed it an input from a super-stable voltage source, and it will scale the ADC inputs from ground up to AREF with the full 10 bits of precision. Of course, you need to make sure none of your analog inputs go over AREF if you are using it like that.

The D11 and E11 Cap is for smoothing out voltage jitters and noise.
Motors, and therefore servos create electrical spikes which can mess up sensor readings, they can also create sudden drains on the battery, so the cap helps keep the robot alive.

From the tutorial
Quote
The large capacitor is not entirely necessary, but is good to help reduce electric noise and keep the system powered during sudden power drains. Even a short lived sudden drop in power could reset your robot microcontroller (bad). The value of this capacitor doesn't really matter, but 100uF and above is a good starting point. More servos you use, the higher you want it to be. It should also always be rated twice that of your input voltage. Your input voltage is ~6V, so you would want it rated for 10V or 15V.

Is that what you needed?


 
  Voyager2
« Last Edit: November 14, 2011, 08:09:14 PM by voyager2 »
And Admin said "Let there be robots!"
And it was good.

Offline schoebyTopic starter

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Re: newby question about capacitors
« Reply #2 on: November 16, 2011, 09:09:04 AM »
Aha thank you.  That helps.  I still have a lot to learn before I know why that value is needed and why it is located there, but that direction gives me key areas to read up on.

 


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