Electronics > Beginners

Multimeters and Resistors

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David Hess:

--- Quote from: The Soulman 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.  :)
--- End quote ---

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.

Russ:
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

Kohlrak:

--- Quote from: Russ on November 26, 2017, 04:53:59 pm ---
--- Quote from: Kohlrak on November 26, 2017, 02:15:04 pm ---
--- Quote from: The Soulman 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.  :)

--- End quote ---

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.


--- Quote from: IanB on November 26, 2017, 03:23:42 am ---
--- Quote from: Kohlrak on November 26, 2017, 12:27:21 am ---none of the resistors are supposed to have a 5 or 6 as a second digit
--- End quote ---

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

--- End quote ---

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.


--- Quote from: IanB on November 26, 2017, 04:18:25 am ---
--- Quote from: Russ on November 26, 2017, 04:05:36 am ---I attached a color code chart from the textbook.

--- End quote ---

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.

--- End quote ---

I 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 am ---
--- Quote from: IanB on November 26, 2017, 04:18:25 am ---
--- Quote from: Russ on November 26, 2017, 04:05:36 am ---I attached a color code chart from the textbook.

--- End quote ---

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.

--- End quote ---


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

Russ

--- End quote ---

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

--- End quote ---

   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

--- End quote ---

Money 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 pm ---
--- Quote from: The Soulman 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.  :)
--- End quote ---

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.

--- End quote ---

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.

Russ:
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

Nerull:
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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