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Topic: 220 ohm resistor in 'FADE' example? (Read 1 time) previous topic - next topic

MikePett

Hi,
 Total newbie here and I am sure that my confusion is based on my own ignorance but every LED I have tried with the 'fade' example has required that I omit the 220 Ohm resistor (red red yellow). I not sure if the Mega2560 has the pull down resistors turned on or what but no matter how many times I load the software and or swap out the LEDs I get the same result, nothing, if the 220 ohm resistor is in place. This is true even when I bypass the circuit board entirely and feed the LEDs right from the gnd and +5 pins. Admittedly the LEDs get hot fast when I wire them right to 5 volts and don't seem to be over heating when I operate them through  fade example , successfully by the way, without the 220 ohm resistor.
 By some coincidence are all of my LEDs made with internal resistors?
Thank you for any light you can shed on this.

MikePett

I am using the arduino mega 2560 and the 0022 alpha software.

PaulS

Quote
I not sure if the Mega2560 has the pull down resistors turned on

Why don't you? They are not turned on by default, so if they are turned on, you did it.

Post your code if you don't know how to tell if you did it.

retrolefty

#2
Dec 29, 2010, 02:30 am Last Edit: Dec 29, 2010, 02:38 am by retrolefty Reason: 1
Quote
220 Ohm resistor (red red yellow).


That would be in fact a 220,000 ohm resistor, must too high a value to light a led up. You need a red, red, brown resistor to equal 220 ohms.

http://www.google.com/imgres?imgurl=http://www.leonaudio.com.au/res-code.gif&imgrefurl=http://www.leonaudio.com.au/res_code.htm&h=1018&w=686&sz=27&tbnid=eNAR-clnfWTcKM:&tbnh=150&tbnw=101&prev=/images%3Fq%3Dresistor%2Bcolor%2Bcode&zoom=1&q=resistor+color+code&usg=__hEZmxaXf7C2iMX8UMfaNU1LxHNY=&sa=X&ei=sI4aTbH5HZG8sQPo4cjMCg&ved=0CCkQ9QEwAQ

The real lesson to be learned is that one [glow]must[/glow] first buy even a simple digital multimeter if they want to build or experimate with stuff using an Arduino. I never trust my eyes on resistors as colors can be faded or even missing. Just measure the resistors with your meter and you won't get rude suprizes like this.

Lefty

CrossRoads

There are NO internal PULLDOWN resisters, only Pullup. See section 12.2 of the ATMega2560 datasheet.
http://www.atmel.com/dyn/resources/prod_documents/doc2549.pdf
9.2MB, is huge.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

PaulS

Quote
There are NO internal PULLDOWN resisters, only Pullup.

Yeah, yeah. I knew that. I knew they pulled one way. Just forgot which. I'll try to pay better attention next time.

Coding Badly


That will be a quarter in the AVR blasphemy jar, please.   ;)

CrossRoads

Hi Paul, did you get a chance to look at the code I PM'd you about?
I can't see why that simple code is losing time so quickly.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

CrossRoads

Coding,
If you could also, I'd appreciate it:

Can you take a look at the code listed in reply #18 here
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1292540097/15
Warren has a simple count up timer intended to be used as a stopwatch eventually, except it seems to lose a lot of time pretty quickly, 2 seconds in just 5 minutes.
Pretty straightforward code, I talked him out of a bunch of floats and dividing down & messing with remainders & stuff. Just 6 counters, if hit 10 or 6 increment the next one in line & clear to 0.
Shift the count out every 10mS.
Thanks
Robert
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Coding Badly


If Warren Reeve doesn't respond in a day or two, prod me and I'll disclose the flaw.

MikePett

Thank you everyone for your informative and highly knowledgable help! You Rock one and all!

I thought that I could trust the chart that I was looking at and I can, it clearly says 220K and I read it as 220.

Here is my quarter.

MikePett :)

retrolefty

Quote
Here is my quarter.


Keep it towards buying that difital multimeter you need.  ;)

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