Help with resistors

[mrtinb]

Hi

In this other thread (Creating Wilf Rigter's ZXKBD v3), I'm building my first circuit for the ZX81, and I'm learning a lot about electronics on the way.

I need two different kind of resistors for this. 10K ohm and 5.1K ohm.

• I have received a package with 10K ohm resistors that I've ordered. The label says 10K, but the colors are Brown, Red, Black, Black, Brown. I'm not very experienced with electronics, but my book says that that is 1.2 ohm. When I use my multimeter set at "200k", then the display says "10.0". Can anyone tell me if this is the correct resistor, that has been shipped to me?
• I have 2.2K, 2.7K, 200, 10K resistors. I need 5.1K ohm resistors that I forgot to order. Can any of the resistors I have be combined to this value?

[1024MAK]

• I have received a package with 10K ohm resistors that I've ordered. The label says 10K, but the colors are Brown, Red, Black, Black, Brown. I'm not very experienced with electronics, but my book says that that is 1.2 ohm. When I use my multimeter set at "200k", then the display says "10.0". Can anyone tell me if this is the correct resistor, that has been shipped to me?

Hi

There are on-line resistor colour code calculators like this one that help. Note that any calculator cannot handle all the variations used by resistor manufacturers over the years. So it may not get it right every time.

Now, resistor colour codes come in a number of variations. The clue is the number of bands and the colours of the last two. Of course, the tricky bit is, which two are the last two....

With your "10kΩ" resistor, the code can be either:
Brown, Red, Black, Black, Brown
or
Brown, Black, Black, Red, Brown

So we decode both:

Brown = 1, Red = 2, Black = 0, Black = X 1, Brown = 1%
= 120 X 1 = 120Ω

but reading the other way gives

Brown =1, Black = 0, Black = 0, Red = X 100, Brown = 1%
= 100 times 100 = 10000Ω = 10kΩ
Note: this is for resistors with a four band colour code to make the number / value. There also exist resistors with a three band band colour code to make the number / value, these have the tolerance (brown = 1%) followed by a red band indicating the temperature coefficient += 50ppm/°C.

• I have 2.2K, 2.7K, 200, 10K resistors. I need 5.1K ohm resistors that I forgot to order. Can any of the resistors I have be combined to this value?

If you connect resistors in series ( one lead connected directly to the lead of the next resistor), the combined value is the sum of all the resistors in the series chain. So you have a choice of 2.2kΩ + 2.7kΩ = 4.9kΩ, or 2.7kΩ + 2.7kΩ = 5.4kΩ

If you connect two resistors of the same value in parallel, (leads connected together at each end), the resulting resistance is half the value of the resistors.
So two 10kΩ resistors connected in parallel gives 5kΩ.

In practice, most circuits are fine with a slightly different resistor value, so either 4.9kΩ, or 5kΩ should be okay.

I hope that helps

Mark

[mrtinb]

I hope that helps

Thanks. That helped a lot.

[PokeMon]

The 5k1 array is a pullup resistor network. So a single resistor wouldn't help.
You have to wire them to a network. All ends together soldered and the other end used for every signal.

[mrtinb]

The 5k1 array is a pullup resistor network. So a single resistor wouldn't help.
You have to wire them to a network. All ends together soldered and the other end used for every signal.

In the PCB design I already changed the resistor network to single resistors.

[mrtinb]

Note: this is for resistors with a four band colour code to make the number / value. There also exist resistors with a three band band colour code to make the number / value, these have the tolerance (brown = 1%) followed by a red band indicating the temperature coefficient += 50ppm/°C.

The book confused me, as I didn't know about three band and four band resistors. The book only showed three banded resistors. It didn't help either, that the silver band was invisible in the printing of the book.

Thanks for your help.

[RWAP]

It has also been pointed out (on Facebook) that the colour banding in the Maplin catalogue has been wrong for years!

[1024MAK]

It has also been pointed out (on Facebook) that the colour banding in the Maplin catalogue has been wrong for years!

But keep in mind, Maplin mainly referred/refer to a slightly unusual band number code, as their 0.6W metal film resistors use two bands for the number, one for the multiplier, one for the tolerance and a final red band for the temperature coefficient. Where as most other five band resistors use three for the number, one for the multiplier, and finally, one for the tolerance.
If you go back in history, the 20% resistors only had three bands... as they did not bother with a tolerance band. And some power resistors use a letter/number code...

So as is typical, if in doubt add a new "standard" or extend the existing "standard", because you can't have too many

Mark

[gozzo]

Maplin resistor code is 3 bands for value, one for multiplier, one for tolerance..the tolerance band being brown and spaced away from the other ones....they have been like this all the time since i have been ordering from maplin (mid 1990s)

[RetroTechie]

The book confused me, as I didn't know about three band and four band resistors. The book only showed three banded resistors.

Book wrong... There's even more possibilities: (for a nice source, check TI Analog Engineer's Pocket Reference)

3 bands: digit - digit - multiplier
4 bands: digit - digit - multiplier - space* - tolerance
5 bands: digit - digit - digit - multiplier - space* - tolerance
6 bands: digit - digit - digit - multiplier - space* - tolerance - temp. coefficient

* usually there's more spacing between digits/multiplier and tolerance bands.

For through-hole resistors the most common tolerances are 5% (gold) or 2% (red), and values <100 Ohm or >10M are much less common than values around 1k-100k range. Which in turn affect what color bands you'll mostly encounter as multiplier. Also gold (5% tolerance) and silver (10% tolerance) can't represent any starting digit.

All in all it doesn't happen often that you encounter a resistor with ambiguous color code. It just takes a little practice (and a decent light source to tell some colors apart ).