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Question about Resistors Answered

I have am writing an arduino sketch for a mini traffic light projects that will require both 220Ω & 330Ω resistors, I ordered them, the problem is that the resistors I received don't add up when looking at the bands.

this is the color band 

ORANGE+ORANGE+BLACK+ORANGE+BROWN

3 -------------3------------0----------x3------------1%--------

does not this mean 330 x 3 @ 1% so the 330 is actually 3,300 or would it be 330kΩ

It's been years since I've looked up color bands , can I even use these ones for simple 5v led projects or should I just re-order the 330Ω resistors now?


thanks in advance
robert




 

Discussions

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Downunder35mJosehf Murchison

Answer 2 years ago

1+
But why do you need resistors with such low tolerances?
The standard ones should be good enough !?

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rdlockreyDownunder35m

Answer 2 years ago

thank you for everyone's input, that's awesome!

I'm only a novice compared to people here, truth is that tolerances is one subject I know little about, just trial & error with my first attempt.

In this case I know enough to know I need to use resistors with LEDs & that each color draws a different current.

when sketching out my plans I used the ohms rule based on specs for the 5v/ 5mm LED's that I had in stock, I calculated that I needed 220Ω& 330Ω for red&green respectively. I think the yellow will use a 220Ω

As I look at the sellers ebay page I see he sells about 40 different variants of resistors, I was infact sent 220kΩ & 330kΩ

basically I know what I need, but have no clue what I have! I was somehow hoping these would work still with my limited knowledge of resistors

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Josehf MurchisonDownunder35m

Answer 2 years ago

The Arduino kit I have came with 1% resistors but I don't think 5% have ever been a problem when I used them.

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rdlockrey

2 years ago

thanks eveyone for your help!

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-max-

2 years ago

Probably a mistake, I generally check suspicious resistors with a multimeter to see if they are within tolerance and the value you expect.

3.3K should be just fine for "good" LEDs. Typically you do not need to drive LEDs at the maximum 20mA to see them, good LEDs will be visible at just a few microamps. I have even used 1megaohm resistors for some of my LEDs, they work fine from that.

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rdlockrey-max-

Answer 2 years ago

interesting... so what would it be effected? the brightness of the led?

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-max-rdlockrey

Answer 2 years ago

You should definitely learn how to use your equipment, the most essential tools for an electronics enthusiast are a good multimeter and an oscilloscope.

There are many great tutorials out there on how to use multimeters and scopes, I especially like YouTube tutorials, made my ElectronicsNmore, Xjet, RCmodelReviews, EEVBlog, AfroTechMods, PowerMax, and several others!

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rdlockrey-max-

Answer 2 years ago

good advice.... I ordered a Velleman HPS140i handheld for just over $100, they are handy & your right I should be doing things right not always trusting what im buying meets the specs it claims.

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-max-rdlockrey

Answer 2 years ago

IMHO, the typical handheld scopes are a waste of money. If you can, I'd recommend returning it, as much better options are available, especially if portability is not required. The screen is too low resolution (and monochrome) and too slow refresh rate for any real debugging, and you will need to be very patent with the clunky interface.

I think you will find a second hand analog scope far, FAR more usable, and often you can pick those up for <$50. Or you could save up and get a good entry level DSO, I personally got the Rigol DS1054Z, for the costs of 4 of those have FAR more functionality:

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- 4 channels to measure multiple signals simultaneously; useful for debugging serial lines, or multiple stages of an analog circuit, etc.

- Intuitive knobs that let you make adjustments quickly and easily

- A much higher resolution 480p color display WITH persistence; there is an EEVblog video that explains why this is a good feature. With the larger screen, much more information can be displayed. due to the low resolution, small spikes, that scope might simply not be able to capture and show you. Analog scopes and good DSO's are needed for that.

- Of course, the 100MHz (hacked) bandwidth and 1GS/s sampling is much better, especially if you need to deal with really fast signals, with 24Msamples of memory, to allow all the finest details to be captured.

- Serial triggering and decoding, math functions, FFT, SD card save, features are nice and just further increase the functionality.

- XY mode, which allows you to trace responses of components like capacitors, inductors, diodes, LEDs, etc. (although XY mode is often a job best left to typical analog scopes)

- list goes on and on and on.

This video dave "reviews" this scope, although really it's more of a rant lol!

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-max-rdlockrey

Answer 2 years ago

The current through an LED is really strange, because a small change in voltage across them results in a HUGE change in current. (in fact, the curve can be approximated with the yellow exponential function.) take a look at this I-V curve, posted below.

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The blue line represents 12V supply of power with a 2.7K resistor in series. Open circuit voltage is 12V, but as you draw more current, the voltage sags quite dramatically. You need to look at the curve kinda sideways to see that. in fact, even with a dead short (0V,) only 4.444 mA would flow, because the resistor limits current. The Q point, (or as I call it, the "happy" point) tells you the voltage and current the LED will operate at. The green line is a linear approximation of the characteristic of a diode near the Q point. Dynamic Z (Z means impedance) simply represents how steep the green line is, or the slope.

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So why not just power this specific green LED with exactly 2.125V to get ~10mA?

Good question, one reason is that it requires precisely tuning the voltage of a regulator for each slightly different LED. The bigger reason is that as LEDs heat up, the entire V-I curve will shift left, and if you are forcing 2.125V across it, so just imagine how high the current can skyrocket! This leads to thermal runaway, and exploding LEDs.

Capture.PNG
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rdlockrey-max-

Answer 2 years ago

interesting...

I tried this 330kΩ resistor with a LED & 5v 500ma adaptor (it was handy) and the led was very dim, I then tried a 5v 2A adaptor & it appeared the same so I then tried a 12V 2A adaptor from my boombox & it still appeared the same, if there was any change between them it wasn't obvious.

I thought it was the current (amps) that would more affected the brigtness not so much the voltage.

Ill study your diagram until I get it, I need to get my game on, I ordered a bunch more arduino stuff, so ill have learn fast!

what about these SMD Chip Resisitors .. are they any advantage?

thanks again

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-max-rdlockrey

Answer 2 years ago

Oh, 330 kOhms, I think your right. Even with 12V, you will have less than 30 uA (microamps). Going from 5V to 12V should have increased the brightness a good bit, by causing a greater voltage to develop across the resistor and therefore a greater current through the LED.

Current and voltage go hand-in-hand, both contribute to the power the LED uses.

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To understand the blue line, imagine you have a voltage supply, 10V, with a 1k resistor in series. When free end of the resistor is not connected to anything, the voltage between it and ground should be 10V.

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As soon as you start connecting things that draw current, then a voltage will develop across the resistor. That voltage drop depends on the current flowing out of the resistor, Vout = 10V - (I*R). The "IR" term is just Vdrop across the resistor, ohm's law. This effectively gives you the equation for that blue line, mathematically stating the relationship of voltage and current.

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See where the lines intersect? Because the LED and resistor are in series, the current through that series must be equal. That's KCL (Kirchhoff's Current Law) It makes sense because the charges going into a wire or component have to come out somewhere, in a series they only have one way to go. Also, because the anode of the LED and the end of the resistor are electrically the same point when connected, the voltage has to be the same! The only place on the curve this ever occurs is where the graphs intersect!

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Josehf Murchison-max-

Answer 2 years ago

I knew I forgot to say something.

+1 check them with a meter.

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rdlockreyJosehf Murchison

Answer 2 years ago

I have a really good fluke meter but I dont know enough about them to test them...

are these resistors/transistors testers any good or do they suffer from the effects of the same cheap components I should avoid?

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Josehf Murchisonrdlockrey

Answer 2 years ago

I have Fluke, GoldStar and a number of other digital multi meters.

The reason I have so many is I reverse engineer and one fits the job better than others, but all are about 1% accurate. They are ballpark enough to tell you the color code is right.

What makes testing with a meter a challenge is reading the display with the auto range, it takes practice to read them at a glance.

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rdlockreyJosehf Murchison

Answer 2 years ago

but wouldn't I want to avoid auto ranging & just manually select the closest range -1 ?

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seandogue

2 years ago

confirm using a dmm. Chinese inks are notoriously vague with respect to the color. sometimes violet, orange and red are almost identical. Same goes for green and blue. 1% metal film have become the most common type, which is why they're so often used.

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rdlockreyseandogue

Answer 2 years ago

copy that... I got the cheap ones only $150 for 10 of them

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Nematic!

2 years ago

they are 330 kΩ resistor.