Author Topic: Multimeters and Resistors  (Read 12547 times)

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Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #25 on: November 24, 2017, 01:52:24 pm »
So it's not scientific notation, but a direct "see 2 color numbers, with this many zeros after it decided by third band." That makes it easier. So black brown black for 1 ohm.

The third band is a multiplier: x0.1, x1, x10, x100, etc.

Therefore 1 ohm is brown black gold (10 x 0.1 = 1).
The easiest method to sort this color coding in someones head (my own opinion) is that you learn that black = 0, brown = 1, Red = 2, Orange = 3 and then learn (...to read from the cheat sheet like pros do) the data represented in each band. ie. Brown-Black-Red-Gold is in plain human language. One - Zero - Two zeros - tolerance +-10% from nominal value, which makes a 1000 ohms nominal and 1k in engineering lingo. Letter k comes from the word kilo, which means thousand (https://en.wikipedia.org/wiki/Metric_prefix).

The trap here, is that when you get first resistor in your hands that do have 5 or 6 bands you are totally lost a moment since it does have three value bands and multiplier band, again do like pros do, look from the fact/cheat sheet.

In moment of panic and self-doubt use the meter to make a sanity check. If that doesn't help take a hammer.

The correlation to colors and 0s was already sinking in just before reading this. So i assume that, too, 5 and 6 band ones work exactly the same way, instead of the 3rd being a decimal or some other unnecessarily convoluted system?
The resistors that do have more than 4 bands are a bit unclear as what each do mean. In resistors 5 to 7 bands the three first bands represent a value and fourth is multiplier. Yes you are in correct path with your thoughts. The next band (5th) is pretty safe to assume to be always the tolerance, but the rest of the bands can generally be pretty wildly anything, however the 6th band is typically a multiplier for the temperature dependency of the resistance (in parts per million = ppm). The inconsistencies of the system comes from the fact that the coding system have its roots somewhere in 1920s or 1930s with only 3 color bands and fixed +-25% tolerance (or something huge from todays perspective).

Edit. PS. Also the body / background color do have its own meaning coded to it, but it is chosen freely by manufacturer as far as I know. Although everyone tries to copy each other and keep the system somewhat logical.

Edit2. Hopefully I didn't wrote a total gibberish as sometimes happens when thinking with two languages simultaneously.

So if i see 4 bands, interpret as normal. 5 bands, i basically handle it the same way, just moving what i consider the 4th band to the 5th band position. 6 and 7 bands, I treat as 5 bands with extra info that I probably don't need, because that is extra information that i wouldn't get with other bands. Unless, of course, i needed that information in the first place, where i'll probably get a proper key for the meaning of those bands with the resistors themselves. Except in special cases where i'm dealing with something someone else made instead, where i essentially have to track down the manufacturer and hope play nice and tell me what they really mean. But basically, 6 and 7 are company standards, as opposed to universal standards like the first 5 bands.

Quote
From all of the posts, I have determined that you have a situation where you are "caught between a rock and a hard spot", since you are having troubles reading color bands and also having trouble reading your resistances on your meter. I truly have the color band reading problem as well, so I use my meter.

Pretty much. But now that I have reliably tested my meter and know it is accurate, i managed to build a 2 resistor cheatsheet (2 resistors sacrificed to paper with their proper values written on them to calibrate against other multimeters if mine somehow goes bad).

Quote
With that said, IMHO, I would would op to simply learn how to use the meter and check each resistor for resistance. I have setup a place on my breadboard for checking resistors quickly by touching a couple of bare wires, which I have set apart a nominal distance and I have my meter leads connected via quick grab clips. I don't even bother looking at color codes unless I am stuck some place without my meter, at which time I always seem to figure out the resistance from the color codes if they are 4 band after looking at different angles and varying light (takes forever).

And it's not helping that the reflection half blinds me.

Quote
I also recommend that you study a book on basic electronics before you hurt yourself. There are plenty of good books and online tutorials available. Your comment about checking the resistance with your meter and being concerned about your heart has given away that you are not learned at all about electricity and electronics. The resistance of your body was causing the different readings while touching the leads. The meter output is such high resistance and low voltage that you would not be harmed by the current.

I exaggerated a little for humor. Though, when my results varied considerably i found it strange. especially when the leads were directly touching the leads of the resistor. By touching the leads of the multimeter the resistance went down which confused me. I would say it was the result of oil from my skin, but when i pinched 1 end together and touched the other lead of the multimeter without touching the resistor, it still went down which does actually confuse me.

That said, I only played this dangerously because the multimeter is powered by a 9volt, and i'm pretty sure the capacitor wouldn't be able to hold enough to fry me. Believe me, i have done some stupid things in life before, so i learned my lesson a long time ago. For fun, the worst one i've done was when i was in single digits (or just into double digits, while i'm 28 now), I wasn't thinking and when a cord got stuck in the power strip, and my wise self felt it was necessary to use my middle finger for leverage... between the prongs... Fortunately, i was on the 3rd floor of a cement building, so it found my finger to be the path of least resistance, as opposed to my leg or something which would've taken my heart. On the flip side, both places i've worked (a chicken factory, and a nursing home) i've gotten shocked by the equipment (a conveyor belt and air sucker at the chicken factory, while a convection stove and a steam table at the nursing home) not being properly grounded. I'm pretty sure there was enough current both times that it would've got us (as in, i wasn't an electrician, but a regular worker, and other people were getting shocked) killed if it was more than just a single arm making the connections. What's worse is, the chicken plant was a fairly wet environment.

I do appreciate your concern, though. You have to be careful when working with stuff like this, which is precisely why i want to avoid AC, since it's way more dangerous than anything i'll be working with, because I know sometimes i forget something's connected after i get brain fatigue.
« Last Edit: November 24, 2017, 01:55:54 pm by Kohlrak »
 

Offline kalel

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Re: Multimeters and Resistors
« Reply #26 on: November 24, 2017, 02:05:28 pm »
There are at least two factors that will affect the resistance measurements that I consider as a newbie. I know there will be many others that I don't even know about.

1 - Touching any of the exposed probe contact of the resistor can affect the readings
2 - Pressure is important, the probe should have solid contact with the resistor leads, that's why the clamp probe can be easier to use (plus makes it easier not to touch the component or probe while measuring)

Of course if the resistor lead or the probe is more oxidized than usual for whatever reason, that oxide layer might affect the readings, but I haven't had such an issue yet.
 

Offline daybyter

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Re: Multimeters and Resistors
« Reply #27 on: November 24, 2017, 02:09:14 pm »
I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.
 
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Offline kalel

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Re: Multimeters and Resistors
« Reply #28 on: November 24, 2017, 02:11:02 pm »
I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.

This is a good idea for some other components as well.
 

Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #29 on: November 24, 2017, 02:25:32 pm »
There are at least two factors that will affect the resistance measurements that I consider as a newbie. I know there will be many others that I don't even know about.

1 - Touching any of the exposed probe contact of the resistor can affect the readings
2 - Pressure is important, the probe should have solid contact with the resistor leads, that's why the clamp probe can be easier to use (plus makes it easier not to touch the component or probe while measuring)

Of course if the resistor lead or the probe is more oxidized than usual for whatever reason, that oxide layer might affect the readings, but I haven't had such an issue yet.

At this point I want to avoid much more spending until i can get a decent job. But, in between (calming my mind), I want to work with this stuff after i finished making my universal assembler (programming assembler) project.

I just got me a pack of envelopes (just regular letter envelopes). You can buy a pack of 50 or 100 for cheap.
Then measured my resistors and put those with the same value in the same envelope and wrote the value on the envelope.
Then put the envelopes in a paper box, where I keep them sorted.
That is a very cheap and compact solution.

You, sir, are brilliant.
 

Offline cowana

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Re: Multimeters and Resistors
« Reply #30 on: November 24, 2017, 02:42:17 pm »
Though, when my results varied considerably i found it strange. especially when the leads were directly touching the leads of the resistor. By touching the leads of the multimeter the resistance went down which confused me. I would say it was the result of oil from my skin, but when i pinched 1 end together and touched the other lead of the multimeter without touching the resistor, it still went down which does actually confuse me.

Your body has a resistance too - so when you hold (the metal of) one multimeter probe in each hand, it will display the resistance of *you*. If you're trying to read the resistance of a resistor at the same time, you'll get the parallel combination (which will be less than the resistor on it's own). The higher the value of the resistor, the more pronounced this effect.
 

Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #31 on: November 24, 2017, 03:53:15 pm »
Though, when my results varied considerably i found it strange. especially when the leads were directly touching the leads of the resistor. By touching the leads of the multimeter the resistance went down which confused me. I would say it was the result of oil from my skin, but when i pinched 1 end together and touched the other lead of the multimeter without touching the resistor, it still went down which does actually confuse me.

Your body has a resistance too - so when you hold (the metal of) one multimeter probe in each hand, it will display the resistance of *you*. If you're trying to read the resistance of a resistor at the same time, you'll get the parallel combination (which will be less than the resistor on it's own). The higher the value of the resistor, the more pronounced this effect.

I thought the resistance of my body was too high to have the parallel effect (just like how air doesn't count). But, now that i think about it, it does make sense.  The resistance is still present across the same circuits, but if i can let even the slightest amount of current from that 9v through me, it'll take some of the resistance away. I still do wonder what the threshold for current flow is. In a pure math world, everything's constantly conducting in the slightest amount (too small to measure), but in the real world that's not the case (at least by our understanding). There's a noticeable threshold for when an arch happens and when it does not. Presumably, this should be the case for all materials. So at what current value (according to ohm's law) does current actually flow?
 

Offline cowana

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Re: Multimeters and Resistors
« Reply #32 on: November 24, 2017, 05:49:34 pm »
There's a noticeable threshold for when an arch happens and when it does not. Presumably, this should be the case for all materials. So at what current value (according to ohm's law) does current actually flow?

Most materials have a voltage at which they break down (ionise), and a much larger current (arc) can flow. For air, this is somewhere around 3kv/mm.

For humans, a very high voltage (around 500v) can cause dielectric breakdown of the skin, allowing very large currents to flow. Before this point, the skin will present a modest resistance (a few 10k ohms) - meaning a small current can flow. Even applying 0.001v across your hands will cause some (very tiny) current to flow across your chest - it's just so low you don't have to worry about it. Generally you can consider around 50v to be the threshold where things could get dangerous.
 
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Offline David Hess

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Re: Multimeters and Resistors
« Reply #33 on: November 24, 2017, 05:56:42 pm »
Anyway, the bane of my existence and learning experience is these resistor color codes. I'm not color blind, but half the time i'm looking at these things, I can't tell yellow from red from orange, red from brown from orange, you get it.

With experience, you get an idea of what values are invalid although that is not much help distinguishing 2.2k from 22k.  But reading the later backwards reveals 3.2k which is not a standard value.
 

Offline GreyWoolfe

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Re: Multimeters and Resistors
« Reply #34 on: November 25, 2017, 07:49:41 pm »
Here's a picture of the meter measuring a 1.8 k resistor (1800 ohms) on the 2000 ohms range:



This should be framed--a HF meter that actually works.  I had 2 of them, new in the package with new batteries added, that measured a 30R resistive element at over 250R.  My Aneng 8008 reads it correctly.  They were free so I obviously got what I paid for.  One of my co-workers loves HF and their free coupons.  After him giving me the 6th free meter, I had to ask him to stop. |O
"Heaven has been described as the place that once you get there all the dogs you ever loved run up to greet you."
 

Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #35 on: November 26, 2017, 12:27:21 am »
Here's a picture of the meter measuring a 1.8 k resistor (1800 ohms) on the 2000 ohms range:



This should be framed--a HF meter that actually works.  I had 2 of them, new in the package with new batteries added, that measured a 30R resistive element at over 250R.  My Aneng 8008 reads it correctly.  They were free so I obviously got what I paid for.  One of my co-workers loves HF and their free coupons.  After him giving me the 6th free meter, I had to ask him to stop. |O

Mine works, too, as far as i can tell. I have a resistor value i'm not supposed to have, but the colors i'm seeing (either black, green, or blue on band 2) suggest that i have resistors that i'm not supposed to have (none of the resistors are supposed to have a 5 or 6 as a second digit, and I can already confirm at least one accurate resistor).

As a side note, avoid those eye tests online. I decided to use php (since i hate javascript) and wrote this code ('cause i naturally didn't trust the answers when everyone who is doing those tests online is selling glasses which are possible only in theory):

Code: [Select]
<?php
        srand
();
        
$kitty rand(099);

        
//Background colors
        
$bgr 255;
        
$bgg 255;
        
$bgb 255;

        
//Foreground colors
        
$fgr 0xF4;
        
$fgg 255//1111 1100
        
$fgb 255;
?>

<html>
        <head><title>Colors</title></head>
        <body style="<?php printf("background-color: #%02x%02x%02x; color: #%02x%02x%02x;"$bgr$bgg$bgb$fgr$fgg$fgb);?>">
        <?php printf("%d"$kitty); ?>
        </body>

Supposedly my red is more sensitive than my green (or that they're equally sensitive). So what i did was do a binary search on green to find out where i last couldn't see the number (0xF4, whereas i could read it at 0xF3), then slowly backtracked on red (since it was so close to 0xFF on green) and stopped at 0xF4 since clearly i wasn't getting anywhere. Now, potentially i'm red colorblind, but we're supposed to see more green than read. Those sites are trying to sell glasses. My girlfriend who's eyes aren't that great (she been diagnosed with everything except colorblindness) I had tested with the same screen (important to do), and it would seem I see green better than her. Now, while it is possible that I see everything better than her (likely, actually), it's quite clear that if i am colorblind, it's way too acute.

Something else to note: the test never bothered to have some sort of calibration for my screen coloring. Although my method didn't, either, I also had another person to test my results against. So, the logical conclusion is, that beautiful gloss tied with the tiny size of those bands (and i don't have magnifying glasses) had me unable to distinguish between the colors when the more obvious glare was shining back at me. In the future, i'm going to snap pictures of them with my tablet (so that the glare will appear white instead of blinding), which should make it easier, and which i should have done in the first place.
 

Offline The Soulman

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Re: Multimeters and Resistors
« Reply #36 on: November 26, 2017, 01:56:28 am »
Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)
 

Online IanB

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Re: Multimeters and Resistors
« Reply #37 on: November 26, 2017, 03:23:42 am »
none of the resistors are supposed to have a 5 or 6 as a second digit

I doubt that. You are likely to have 15 and 56 in your collection.
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #38 on: November 26, 2017, 03:53:22 am »
From my textbook.
 
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Online IanB

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Re: Multimeters and Resistors
« Reply #39 on: November 26, 2017, 03:56:01 am »
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #40 on: November 26, 2017, 04:05:36 am »
From my textbook.

And?

   I attached a color code chart from the textbook.
 

Online IanB

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Re: Multimeters and Resistors
« Reply #41 on: November 26, 2017, 04:18:25 am »
I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #42 on: November 26, 2017, 04:23:07 am »
I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.


   Yes. But I found that an auto-ranging meter makes quick work of deciphering the Resistor values. 👍😁

Russ
 

Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #43 on: November 26, 2017, 02:15:04 pm »
Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)

LED pen light from my tablet's stylus. Trying regular bulbs doesn't produce enough light, and since i'm in the northern hemisphere, sun isn't much help either. Normally those kinds of things aren't a problem, so when i get up later i'll try again using my camera to magnify them so i can see them better.

none of the resistors are supposed to have a 5 or 6 as a second digit

I doubt that. You are likely to have 15 and 56 in your collection.

I'm supposed to have a very specific set of them. But, realistically, we know these sets and kits rarely ever have what they're supposed to, especially if they have tiny colored markings that're hard to see to help us identify what goes where.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.

I do believe i've found those exact ones. I mounted them to paper with tape and wrote those values on them.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.


   Yes. But I found that an auto-ranging meter makes quick work of deciphering the Resistor values. 👍😁

Russ

If and only if you trust your meter, which I didn't.
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #44 on: November 26, 2017, 04:53:59 pm »
Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)

LED pen light from my tablet's stylus. Trying regular bulbs doesn't produce enough light, and since i'm in the northern hemisphere, sun isn't much help either. Normally those kinds of things aren't a problem, so when i get up later i'll try again using my camera to magnify them so i can see them better.

none of the resistors are supposed to have a 5 or 6 as a second digit

I doubt that. You are likely to have 15 and 56 in your collection.

I'm supposed to have a very specific set of them. But, realistically, we know these sets and kits rarely ever have what they're supposed to, especially if they have tiny colored markings that're hard to see to help us identify what goes where.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.

I do believe i've found those exact ones. I mounted them to paper with tape and wrote those values on them.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.


   Yes. But I found that an auto-ranging meter makes quick work of deciphering the Resistor values. 👍😁

Russ

If and only if you trust your meter, which I didn't.

   I eventually bought a quality meter (EEVBLOG/Brymen 235) and it has been dead accurate. I sometimes use a10x loupe when looking at color bands, and it is still difficult to discern colors at times 😬.

Russ
 

Offline David Hess

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Re: Multimeters and Resistors
« Reply #45 on: November 26, 2017, 04:54:52 pm »
Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)

I was thinking of getting an small LED flashlight for this kind of work but I will have to test this.  The CFL lamps that I normally use do not seem to be a problem.  Below is an example illuminated with a CFL bulb.
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #46 on: November 26, 2017, 05:01:32 pm »
I use a small LED or COB flashlight frequently. I also picked up this assortment of 750 Resisors, dirt cheap.

Cutequeen 750 pcs,30 Values Resistor Kit x 25pcs =750 pcs (10 Ohm - 1M Ohm) 1/4W Metal Film Resistors Assortment https://www.amazon.com/dp/B016NXK6QK/ref=cm_sw_r_cp_api_2jVgAb37R2TN7

Russ
 

Offline KohlrakTopic starter

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Re: Multimeters and Resistors
« Reply #47 on: November 26, 2017, 10:33:09 pm »
Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)

LED pen light from my tablet's stylus. Trying regular bulbs doesn't produce enough light, and since i'm in the northern hemisphere, sun isn't much help either. Normally those kinds of things aren't a problem, so when i get up later i'll try again using my camera to magnify them so i can see them better.

none of the resistors are supposed to have a 5 or 6 as a second digit

I doubt that. You are likely to have 15 and 56 in your collection.

I'm supposed to have a very specific set of them. But, realistically, we know these sets and kits rarely ever have what they're supposed to, especially if they have tiny colored markings that're hard to see to help us identify what goes where.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.

I do believe i've found those exact ones. I mounted them to paper with tape and wrote those values on them.

I attached a color code chart from the textbook.

Of course. And from that chart you can see that a 15k resistor would be brown-green-orange, and that a 5.6 k resistor would be green-blue-red. So if you find resistors with those colors you will know what values they are supposed to be.


   Yes. But I found that an auto-ranging meter makes quick work of deciphering the Resistor values. 👍😁

Russ

If and only if you trust your meter, which I didn't.

   I eventually bought a quality meter (EEVBLOG/Brymen 235) and it has been dead accurate. I sometimes use a10x loupe when looking at color bands, and it is still difficult to discern colors at times 😬.

Russ

Money is an issue for now. All these components i've had for over a year.

Under what light did you read the resistors?
"White" led's aren't white at all just a very poor rgb mix screwing up colors beyond recognition.
Regular light bulbs are much better or try daylight.  :)

I was thinking of getting an small LED flashlight for this kind of work but I will have to test this.  The CFL lamps that I normally use do not seem to be a problem.  Below is an example illuminated with a CFL bulb.

I'll vouch for LED being OK, too. I was able to see it this tim by holding the light either (or both) further away or (and) by holding it at a different angle. The issue is indeed the band sizes tied with the glare. I then turned around and used the camera, which made everything infinitely more obvious. Autofocus doesn't work well, so i won't post the picture, but it was alot clearer before snapping the picture. In the picture, you can see the center of the gold band (the part your eyes would focus on) being completely obscured by the glare from the light. The multimeter is accurate to within the tolerance levels, too, so i now know i can trust it, too. Bought 200 #6 3/4 envelops, so i'lll probably leave the cheatsheet as is for safety and just rely on the multimeter to go through all my resistors quickly, then stick them into labeled envelops, then do a quick look over with my tablet for proper magnification as a double check after they're all sorted.
 

Offline Russ

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Re: Multimeters and Resistors
« Reply #48 on: November 26, 2017, 10:38:43 pm »
I have one of those meters from Harbor Freight. It stays in the car for simple auto measurements. I procured two much better units for all other applications. Yours may be sufficient for what you are doing.

Russ
« Last Edit: November 26, 2017, 11:54:18 pm by Russ »
 
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Offline Nerull

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Re: Multimeters and Resistors
« Reply #49 on: November 27, 2017, 02:40:57 pm »
Light source can absolutely make a huge difference. The color of a material is determined by the wavelengths of light reflected by that material. If that wavelength isn't present in the light hitting the material, it can't be reflected. If you have a continuous spectrum light source, this isn't a problem - all wavelengths are there, so every color gets reflected properly.

Many light sources are not full spectrum - our eyes only see three colors, so we can recreate any light color with just three specific wavelengths mixed together - but quantum mechanics is a little more picky. If a certain wavelength isn't present, it won't be reflected and reflected colors will appear muted and muddy. Atoms can't mix colors to approximate light.





You can image from the color charts that this could make reading color bands much harder.

 
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