Multimeters and Resistors - Page 1
Forum section: electronics / beginners

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 08:14:04 am
content: As you'll see from one of the attachments, I have a mess of parts, wonderful "lab" and all kinds of fun stuff with the lab and didn't come with the lab. I've experimented with ATMega 328P-PUs, got some fun things working for it, but would like to try to make things from scratch that I could drive with it. I have a nifty IR LED with an IR sensitive photoresistor ("receiver"), I even have visual spectrum photo-resistors. I have cool parts and doo-dads, but I'd love to learn how to use them. I got 2 books that came with the lab, 1 book that I bought that i managed to get through (focused on digital circuits). I'm not really interested in AC, outside of making something to convert it to DC (actually, i'd rather not make something that i'd plug into the wall and ends up catching the house on fire).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. I've read other places that the paint jobs anymore are horrible, so it might not just be my eyes. I was hoping to try to gain some familiarity with it (or just straight up make a cheat sheet with contrastive resistors just so i can tell the colors apart) by using the resistor modes on my multimeter, but I don't know what the readout should look like. I also find it strange that everything is in terms of 2, but i'm not sure if I should be dividing or multiplying by 2 to figure out what my resistor is. I figure the black plug should be in "COM" but i'm honestly not sure which plug is should be using for which modes, nor do I know what all the modes are. I think the one mode is a diode mode, which seems absolutely pointless.Honestly, I don't remember if the thing even came with a manual or not, but if it did, it got lost from all the moving of the parts constantly. Supposedly out of my resistor pack from Radio Shack, I have the following.10 of 10?, 1k?, 10k?, and 100k?.8 of 47?, 100?, 470?, 2.2k?, 4.7k?, and 1M?.4 of 150?, 220?, and 15k?.They're all 5% tolerance, so that's easy to identify.Each of 5% tolerance. So, i tried to use that kind of power of deduction that the strips of 10 should be of particular interest to me and be the easiest way to identify what some of the colors are, right? As predictable, either my eyes are really bad, i'm doing this wrong, or the actual number of resistors is not what's printed on the package. Not a big deal for me, as i've bought this stuff a long time ago, but i'd really like to get over this hump.So, I have a few questions (just to get my foot in the door, mostly):1. For those of you who've done this longer than me, out of what was advertised, what combination do you feel to be the most efficient (fewest resistors displaying the most colors) that i could tape to a piece of paper to have a physical cheatsheet for dealing with various lighting conditions?2. What should I set my multimeter to, and what should I expect to see, when looking for the resistors to question 1 (I probably don't need an exhaustive list, if it's alot of work for you)?3. I noticed that my crystals froze the ATMega 328P-PU (Arduino CPU) when one of the capacitors comes undone (22?F, I think, as they just have "22" written on them). When i disconnected both of them from the crystal (16MHz) it worked again. I can't remember if i plugged it directly to ground or not, implying that the capacitors are not actually needed (i wasn't afraid of frying it or anything, since these chips are so cheap). Why is this?4. Realistically, what is the problem with doing this?5. Anything I can do with these to slow them down to 16KHz, or hook them up to something else to use them? I only have 11 ATMega chips, but I have like 50 of those crystals. I was curious if I could make an interrupt timer, buzzer, or something like that out of them, and how I would even go about it (maybe even something sensitive to the photoresistors or the IR detector).

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 08:48:29 am
content: With my resistor pack I wrote the values on the little paper strips they are attached to so I can quickly find a value I want, and I sorted them into one of those multi-compartment project boxes with all the same numeric values in the same compartment. So all the 10, 100, 1k, 10k, 100k 1M into one compartment, 2.2, 22, 220, 2.2k 22k etc into the next compartment, and so on.

author: Brumby
author_rank: Unknown
timestamp: November 24, 2017, 08:58:26 am
content: I could read a resistor colour code from 4 feet away on a carbon film resistor ... but when they introduced the metal film with the blue body, I'm challenged to read some values with my head magnifier at times!!I'd really like to knee-cap the bozos that came up with that.

author: Bashstreet
author_rank: Frequent Contributor
timestamp: November 24, 2017, 09:04:38 am
content: Quote from: Brumby on November 24, 2017, 08:58:26 amYes i do not find those blue ones fun at all... Any case i end up always just using my meter to check the values..

author: Brumby
author_rank: Unknown
timestamp: November 24, 2017, 09:13:04 am
content: I often do, too.

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2017, 09:23:13 am
content: 1. Forget about colour codes, with typical chinese resistors it's so hard to read. That's what a multimeter is for.2. If your multimeter is set to a range which is too low to show the resistor's value it will indicate an overload by printing a "1" in the left most position and nothing else (maybe a decimal point), ie "1 " which is different to " 1". Your meter is manual ranging, each time you go "up" a range (ie from 200 to 2000) you lose 1 digit of precision, that is, the 0-200 range can measure 0.1 ohm units, the 2000 range can measure 1 ohm units, the 20k range can measure 10 ohm units, the 200k can measure in 100 ohm units, and the 2000k (2M) range can measure in 1k units. For example given a resistance of 123 Ohms, the 200 range will show 123.0, the 2000 range will show 123, the 20k range will show 0.12, the 200k range will show 0.1 and the 2000k range will show 0. In other words, just buy an autoranging meter :-)3. The caps may or may not be necessary, and if they are your construction (especially on a breadboard) may well have enough inherent capacitance on it's own. What will not be so good though as you found is to have it unbalanced.4. With the caps? Nothing, it will work (oscillate and therefore the atmega can run) or it won't (in which case nothing will happen).5. You want to run the ATMega a t 16 KILO Hertz? 16KHz is pretty much silly. 16MHz is a standard speed. There's no reason you can't run at 16KHz (I think from memory, you'd have to check the datasheet to be sure), but to be a little blunt if you don't know how to use a multimeter, you are trying to run before you can walk here. Anyway if you wanted to stay within the Arduino environment you would have to create a custom board definition in order to set the AVR frequency in order that timing (millis(), delay() etc) was accurate.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 09:58:11 am
content: QuoteGood to know i'm not a looser for having trouble reading them, then.QuoteMy multi-meter doesn't seem to be that technical (1s are always printed from the right). I'd love to know what i'm supposed to be seeing, but I can never figure out what i'm even playing with to begin with, so i know if i should be dividing the number i see on the screen by 2 or what.QuoteI read that too much capacitance can slow it down, but i'm not sure how much it actually matters at the end of the day. Are we talking 1Hz for every 100 microfarad, or is it 1MHz for every 1 microfarad?QuoteGood, no frying, then.QuoteI'm thinking more in terms of slowing it down and sticking it on another pin (what if i want to know how much time has passed but don't want to count individual instruction cycles, for example?). To throw it at 16KHz, in particular, would be to stick it on a speaker to make a buzzing noise. I'm trying to figure out what I could do to slow it down to find more applications for it outside of a clock for a microcontroller, since i have way more crystals than microcontrollers.QuoteI understand most of the stuff from the atomic level to the programming level, and I even know how to use A multimeter, but i don't necessarily know how this one works, but I also don't have a resistor of known value, so i've run into a chicken-or-egg problem. I've wanted to try my hand at some more analogue circuits using direct current, so i could use my chips for things without buying "shield X" from sparkfun or something. I have a bunch of pieces of things sitting there collecting dust, and I wouldn't mind experimenting with ideas that they don't even have shields for. I've even thought of trying to make some sort of radio receiver to try to pick up truly random noise to quickly generate huge xor encryption keys and things like that.

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2017, 10:09:51 am
content: In any resistance range, show what your meter shows with the leads not connected to anything.In any resistance range, show what your meter shows measuring any resistor.

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2017, 10:14:34 am
content: ALso in the picture of your multimeter, take note that you have the probes in the incorrect sockets for measuring resistance.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 10:20:55 am
content: Quote from: sleemanj on November 24, 2017, 10:09:51 amIt's one of those little CEN-TECH meters from Harbor Freight. It has manual ranges 200, 2000, 20k, 200k, 2000k. It shows 1 on the left of the display if it's over range, otherwise it displays the value.To measure a resistor you start on the 200 range and if the display shows 1 you turn the dial up through the ranges until you see a value. Then you read the value off the display.

author: sleemanj
author_rank: Super Contributor
timestamp: November 24, 2017, 10:25:31 am
content: Quote from: IanB on November 24, 2017, 10:20:55 amYes I have a similar model in front of me, but the poster said his doesn't work like that ("(1s are always printed from the right)") So I'm a little confused.Anyway, to the poster.Make sure that you understand1. To measure resistance you need the probes in the COM and the V/Ohm/mA sockets (the bottom two sockets)2. The symbol for resistance is Omega (a curvey n with feet)3. the resistance ranges bottom left quarter of the dial are 2000k through 2004. the ranges with "k" suffix measure in k, 123.4 means 123.4 kohms5. the ranges without a suffix measure in ohms, 123.4 means 123.4 ohms6. if it prints just "1" on the left side of the display, that means it's over-range, move the dial one place clockwise to go to the next range

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 10:36:10 am
content: Here's a picture of the meter measuring a 1.8 k resistor (1800 ohms) on the 2000 ohms range:

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 10:38:29 am
content: Quote from: sleemanj on November 24, 2017, 10:25:31 amI'm pretty sure it does work like that. I think the OP is just in a bit of a muddle.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 11:07:29 am
content: https://78.media.tumblr.com/569d5f0239d37dc134568fbafd320c8a/tumblr_ojyg1iC6TK1vhaphlo1_r1_500.gifQuote from: IanB on November 24, 2017, 10:36:10 amWhat're the odds you'd have the same one? So, basically, i'm reading the thing wrong, that there's no need to take the output and divide by said number or multiply by said number, which was what i was interpreting so far. So, if I see 1 at 200, I should assume it's either out of range, or i'm dealing with 1 ohm, right?It seems strange to me that it'd have so many modes if the real limitation is the 4 digits. Anyway, it seems at this point my goal is to look for what i think to be brown gray silver gold (I should have one, as i have more than just that one resistor pack), then throw my multimeter to 2000 and make sure it's similar, then see how it reacts when i set it to other ranges.I do assume that if i set the thing to 20k i'll have to add some zeros. How many, though?What's hFE?And what do I do with the, what i'm asusming to be, some sort of transistor testers? There's 4 pin holes for NPN and PNP respectively.QuoteCould be that, too. Issue being, it's hard to concisely experiment when you have 2 variables and no controls. Once I go through these resistors with this image I should be able to go at least a little on my own from there. Just need to figure out how it handles resistors outside of the normal display range at this point, then.As for the other replies, wow, reply rates seem to be much higher here than i'm used to for tech related forums.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 11:14:30 am
content: Quote from: Kohlrak on November 24, 2017, 11:07:29 amA 1.8k resistor (1800 ohms) is brown gray red (18 followed by 2 zeros).QuoteIf out of range the meter shows a 1 on the left and a dot on the right. If you measure a 1 ohm resistor you will see something like 01.3 on the display.

author: Nusa
author_rank: Super Contributor
timestamp: November 24, 2017, 11:15:53 am
content: Since your resistors are conveniently in strips, leave them there until you actually need to use one.All the resistors in the same strip are the same, so measure one without removing it from the strip, then write its value on the paper strip on both sides. You just saved yourself a lot of future measurements or puzzling over color codes.Repeat for your other strips of resistors.It's possible you have a red-green color deficiency mild enough it's never been diagnosed. That is the most common form of color-blindness (a misnomer in most cases, as they still see plenty of color). If so, it just means you see some colors less brightly than some people, which can make reds/browns/oranges hard to identify except in really good light. If other people have no problem reading off the color bands on the same items, then it probably is your eyes.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 11:25:44 am
content: Quote from: Nusa on November 24, 2017, 11:15:53 amToo late for some of them, though I think most of them (the ones with the board) didn't come with strips. If they did, i got excited thinking that reading them from colors would be easy.QuoteTo be honest, the colors when juxtaposed look different, distinctly, but the lighting and such overall makes it rather difficult to tell which color is supposed to be what, even though they are different enough to know that they're different. So, i'm not sure it's actually the eye thing, but incase it is, do you have any images or ways of testing the mildness as opposed to absolute?QuoteSo 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. Seems I dont' have the 1.8k, I have a 1.5k, so i'm looking for brown green red gold. Oh wait, some of these have more than 4 bands...EDIT: nvm, it's 4 bands, it's just weird glare from the lighting in here.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2017, 11:32:07 am
content: Quote from: Kohlrak on November 24, 2017, 11:25:44 amThe third band is a multiplier: x0.1, x1, x10, x100, etc.Therefore 1 ohm is brown black gold (10 x 0.1 = 1).

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 11:42:48 am
content: Quote from: IanB on November 24, 2017, 11:32:07 amSeems more logical to do black brown black, but hey, my job is to read, not to paint them myself. Got one registered 988, definitely looks brown black red. When i changed to 20k, it registered 1.18, so starting when the mode ends with k, i need to add 3 zeros, right? How would it display the 1M ohm and the 10 ohm that are supposedly in here? I assume I go to 2000k, so would it display as 1 and 10 respectively?

author: Nusa
author_rank: Super Contributor
timestamp: November 24, 2017, 11:47:53 am
content: Many informal color tests on the internet. Here's one:http://enchroma.com/test/instructions/Here's the manual for the common centech meter:https://manuals.harborfreight.com/manuals/98000-98999/98025.pdfHarbor Freight periodically has free-with-purchase store coupons, so any hobbyist who lives near a Harbor Freight has probably grabbed one or more over time. Including me.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 12:03:58 pm
content: Quote from: Nusa on November 24, 2017, 11:47:53 amOh wow. And here i thought the diode was to help people figure out which side was which if the paint came off or something. I found one that looks like a 45kohm according to the meter, but it looks to be 46kohm, but i'm not supposed to even have either. The closest one is supposed to be 47kohm, according to the packaging. It's so tiny i just can't tell if that second band is green, blue, or black.Wait, if i hold the resistor's pins against the needles it registers 45.2, but if i lay it down and test it, i get 46.3. It comes from touching the needle, not the resistor, but if i hold the 2 needles like an idiot asking to shock my heart out of rhythm, too much resistance. Lesson learned, put it down on something. But, why that level of change? And how have i not killed myself being an idiot?Well, at least some lessons are being learned.EDIT:QuoteI noticed certain ones did give me a very hard time. And here i thought that green was supposed to be the easiest color for all humans to reliably distinguish, hence why 16bit coloring has an extra green bit.

author: Vtile
author_rank: Super Contributor
timestamp: November 24, 2017, 12:23:54 pm
content: Quote from: IanB on November 24, 2017, 11:32:07 amThe 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.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 12:41:27 pm
content: Quote from: Vtile on November 24, 2017, 12:23:54 pmThe 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?

author: Vtile
author_rank: Super Contributor
timestamp: November 24, 2017, 12:55:44 pm
content: Quote from: Kohlrak on November 24, 2017, 12:41:27 pmThe 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.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: November 24, 2017, 01:26:49 pm
content: 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.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).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.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 01:52:24 pm
content: Quote from: Vtile on November 24, 2017, 12:55:44 pmSo 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.QuotePretty 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).QuoteAnd it's not helping that the reflection half blinds me.QuoteI 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.

author: kalel
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:05:28 pm
content: 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 readings2 - 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.

author: daybyter
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:09:14 pm
content: 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.

author: kalel
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:11:02 pm
content: Quote from: daybyter on November 24, 2017, 02:09:14 pmThis is a good idea for some other components as well.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 02:25:32 pm
content: Quote from: kalel on November 24, 2017, 02:05:28 pmAt this point I want to avoid much more spending until i can get adecentjob. But, in between (calming my mind), I want to work with this stuff after i finished making my universal assembler (programming assembler) project.Quote from: daybyter on November 24, 2017, 02:09:14 pmYou, sir, are brilliant.

author: cowana
author_rank: Frequent Contributor
timestamp: November 24, 2017, 02:42:17 pm
content: Quote from: Kohlrak on November 24, 2017, 01:52:24 pmYour 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.

author: Kohlrak
author_rank: Contributor
timestamp: November 24, 2017, 03:53:15 pm
content: Quote from: cowana on November 24, 2017, 02:42:17 pmI 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?

author: cowana
author_rank: Frequent Contributor
timestamp: November 24, 2017, 05:49:34 pm
content: Quote from: Kohlrak on November 24, 2017, 03:53:15 pmMost 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.

author: David Hess
author_rank: Super Contributor
timestamp: November 24, 2017, 05:56:42 pm
content: Quote from: Kohlrak on November 24, 2017, 08:14:04 amWith 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 astandard value.

author: GreyWoolfe
author_rank: Unknown
timestamp: November 25, 2017, 07:49:41 pm
content: Quote from: IanB on November 24, 2017, 10:36:10 amThis 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.

author: Kohlrak
author_rank: Contributor
timestamp: November 26, 2017, 12:27:21 am
content: Quote from: GreyWoolfe on November 25, 2017, 07:49:41 pmMine 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:<?phpsrand();$kitty=rand(0,99);//Background colors$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.

author: The Soulman
author_rank: Super Contributor
timestamp: November 26, 2017, 01:56:28 am
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2017, 03:23:42 am
content: Quote from: Kohlrak on November 26, 2017, 12:27:21 amI doubt that. You are likely to have 15 and 56 in your collection.

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 03:53:22 am
content: From my textbook.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2017, 03:56:01 am
content: Quote from: Russ on November 26, 2017, 03:53:22 amAnd?

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 04:05:36 am
content: Quote from: IanB on November 26, 2017, 03:56:01 amI attached a color code chart from the textbook.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2017, 04:18:25 am
content: Quote from: Russ on November 26, 2017, 04:05:36 amOf 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.

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 04:23:07 am
content: Quote from: IanB on November 26, 2017, 04:18:25 amYes. But I found that an auto-ranging meter makes quick work of deciphering the Resistor values. 👍😁Russ

author: Kohlrak
author_rank: Contributor
timestamp: November 26, 2017, 02:15:04 pm
content: Quote from: The Soulman on November 26, 2017, 01:56:28 amLED 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.Quote from: IanB on November 26, 2017, 03:23:42 amI'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.Quote from: IanB on November 26, 2017, 04:18:25 amI do believe i've found those exact ones. I mounted them to paper with tape and wrote those values on them.Quote from: Russ on November 26, 2017, 04:23:07 amIf and only if you trust your meter, which I didn't.

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 04:53:59 pm
content: Quote from: Kohlrak on November 26, 2017, 02:15:04 pmI 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

author: David Hess
author_rank: Super Contributor
timestamp: November 26, 2017, 04:54:52 pm
content: Quote from: The Soulman on November 26, 2017, 01:56:28 amI 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.

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 05:01:32 pm
content: 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 Assortmenthttps://www.amazon.com/dp/B016NXK6QK/ref=cm_sw_r_cp_api_2jVgAb37R2TN7Russ

author: Kohlrak
author_rank: Contributor
timestamp: November 26, 2017, 10:33:09 pm
content: Quote from: Russ on November 26, 2017, 04:53:59 pmMoney is an issue for now. All these components i've had for over a year.Quote from: David Hess on November 26, 2017, 04:54:52 pmI'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.

author: Russ
author_rank: Regular Contributor
timestamp: November 26, 2017, 10:38:43 pm
content: 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

author: Nerull
author_rank: Frequent Contributor
timestamp: November 27, 2017, 02:40:57 pm
content: 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.

author: paulca
author_rank: Super Contributor
timestamp: November 27, 2017, 04:42:23 pm
content: As my eyes are deteriorating rapidly in the last 10 years, due mostly to very heavy VDU usage I find it impossible to read the small blue resistors, completely impossible, even with a magnifier inspection lamp.The 5% brown carbon resistors (like from bitsbox) are much easier to read. Even then sometimes they are tricky.So here is what I did.I bought a large compartment box and a pack of known resistors. I placed them in decades eg:10, 100, 1k, 10k, 100k, 1M22, 220, 2k2, 22k, 220k, 2M47, 470, 4k7, 47k, 470k, 4MMost are still on tape strips, but used ones lie loose in the trays under the tape strips.These get me by. Should I ever decide to get the other decades I'll just start another box.When I take a resistor out, I give it a quick glance that it looks "probably right", if I have any doubt I stick it in the breadboard and test it with the meter.When I'm tearing down a breadboard I put them all back where they belong.Of course mistakes happen, I drop resistors into random slots and so forth.What I am planning to get round to is a resistor jig for the meter. Just a couple of old breadboard rails or similar that I can croc clip onto and press resistors against to check them quickly before use or putting back in the compartment box.

author: Vtile
author_rank: Super Contributor
timestamp: November 27, 2017, 05:16:46 pm
content: You can also make something like this. It is made from solid-core mains copper wire and quick glued to some fiber board. The original idea is variation from IIRC Conrad Hoffman's "Minimetrology lab" articles, Conrad is frequently hanging on the Metrology section here at eevblog.

author: kalel
author_rank: Frequent Contributor
timestamp: November 27, 2017, 05:28:12 pm
content: Quote from: Vtile on November 27, 2017, 05:16:46 pmThat looks interesting, where do the measurement/connection to instrument leads go? Unless I got the purpose wrong.

author: Vtile
author_rank: Super Contributor
timestamp: November 27, 2017, 05:31:58 pm
content: Quote from: kalel on November 27, 2017, 05:28:12 pmLike Paulcas plan, I have used just typical croc-clips to these jig arms.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 26, 2018, 03:13:02 am
content: Quote from: Brumby on November 24, 2017, 08:58:26 amNot to worry. Leaded resistors are becoming obsolete and everything is going SMD. They all have the value printed on them. The last digit is the number of zeros and R is used as a decimal point. The down side is you need a microscope to see the #!$%= thing and a whole new set of tools to replace them.Sent from my SM-G900V using Tapatalk

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 26, 2018, 03:36:48 am
content: I think you better get the meter squared away first.On a manal ranging meter, the lowest range that will display the value will give the greatest accuracy. You don't have to do any calculating. Just read the meter. Depending on the range the range the meter might express 1.2k as 1200 ohms. 500,000 ohms is .5 megohms. It is no different than going from mm. to cm. to meters. Work with resistors long enough and the color code will become second nature. Just memorize the colors There are only 12, including gold and silver.Sent from my SM-G900V using Tapatalk

author: Jwillis
author_rank: Super Contributor
timestamp: August 26, 2018, 04:05:03 am
content: A really bright cool white lamp and a pair of 4X reading glasses works for me .A loupe for those smd.s and 1/8W axials.But still measure with an DMM or milliohm meter.One day I'll invest in a Digital microscope.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 28, 2018, 01:35:51 pm
content: Quote from: Jwillis on August 26, 2018, 04:05:03 amReading them is only half the battle. After that you have to replace those little #%=× SMD's. They have special desoldering solder, heat guns, tweezers, flux, vacuum pick ups; ARGHHH!!!! I guess I am going to have to bite the bullet and develop some new skills. With leaded components you could fudge it if the replacement was not the exact same physical size but SMD resistors come in a while bunch of physical sizes.Sent from my SM-G900V using Tapatalk

author: JS
author_rank: Frequent Contributor
timestamp: September 01, 2018, 05:42:01 pm
content: Quote from: 6PTsocket on August 28, 2018, 01:35:51 pmDesoldering TH parts makes pretty likely to break traces, specially in single sided PCBs where they usually grow. SMD parts also can be exchanged between a few sizes, some pretty tight PCB might not allow it but in many they will fit one size up and down. One problem could be power dissipation for parts with tight ratings, where you can't use smaller ones.JS

author: ArthurDent
author_rank: Super Contributor
timestamp: September 01, 2018, 09:46:07 pm
content: One cheap item that could be a big help to you, that could verify what you think your multimeter is telling you, is a component tester. There are a lot of them on Ebay, generally for between $15-$25, and they work well. I have lots of test equipment but for a quick check on a questionable capacitor or a resistor where all the colors are almost indistinguishable, it comes in very handy. The one thing to be very careful of is to make sure any capacitor you are testing is totally discharged or it can zap the tester. Other than that, the tester is almost foolproof and has a very good display with all the information you'll need on any component.

author: tooki
author_rank: Super Contributor
timestamp: September 03, 2018, 12:20:44 pm
content: Quote from: Kohlrak on November 24, 2017, 03:53:15 pmThe resistance of your skin varies wildly based on thickness, where on your body, how dry or moist the skin is, how sweaty it is (sweat = salt = ions = lower resistance), how oily it is, etc.Quote from: Kohlrak on November 24, 2017, 03:53:15 pmIt’s the voltage that pushes current flow, and it’s voltage that causes dielectric breakdown and allows conduction to begin across an insulator. That’s why high voltage can jump across an air gap, ionize the air, and produce a conductive path.I’m no physics whiz, but basically you can consider things to be either conductors (any resistance lower than infinity) or insulators (infinite resistance). For most low-voltage purposes (and certainly the level you’re at), a sort of ballpark is that any resistance up to about 10Mohm is a conductor, and anything much above you can effectively treat as an insulator. Look at the ranges of values that normal resistors come in: from about 1/2 ohm to about 100Mohm: that gives you a decent idea of what is used in most circuits, and even the extents of that are fairly rare. Any resistance below that, we can usually treat as “zero resistance”, and anything above as a de-facto insulator.Of course, there are specialties where this does not apply (like insulation testing for safety in mains-powered devices, or anything high voltage), but you’re not ready to be doing those things quite yet anyway.As for color bands: I can’t emphasize enough how important the light source is. You need lots of light, and it needs to be good quality, as others have said. A little halogen desk lamp can be a lifesaver in this regard.