W A R N I N G !

W A R N I N G !

This page is full of non-facts and bullsh!t, (just like the internet and especially forums and other blogs), please do not believe entirely without exercising your intellect. Any resemblance to real things in reality is purely coincidental. You are free to interpret/misinterpret the content however you like, most likely for entertainment, but in no case is the text written on this blog the absolute truth. The blog owner and Blogger are not responsible for any misunderstanding of ASCII characters as facts. *cough* As I was saying, you are free to interpret however you like. *cough*

Tuesday, October 19, 2010

47kohm resistor vs 50kohm pot

Looking around, I chanced upon people looking for exact values of resistors and capacitors, and people who when they couldn't find the values needed combine stuff - e.g. to get a 47kohm resistor they put 2 22kohms and 1 3ohm in series, that kind of example.

Of course, monkey see monkey do that's why.

Well, first thing, an unrelated but important thing to know, is that the exact value of the potentiometer doesn't matter as long as it is within 10k to 100k with 20k/50k often used (and often argued over which is the better one).

The above fact makes it pointless to ponder one situation. Lets get back to topic.

Have you wondered why are electronic components in weird values like 22 and 47?

There is actual science involved!

Remember physics in secondary school/jc (hope you still do), the thing about number of significant figures and decimal places?

If you use 2.2 to add 3.3, you write it as 5.5 and not 5.50?

It's a similar thing in real life.

Resistors and capacitors, have a tolerance of 20%, unless otherwise stated.

So that means a 1.0 can be anywhere between 0.8 and 1.2.

If this is the case it does not make sense to have values of 0.9 and 1.1 right?

Nor 1.2 - 1.2 can be 0.96 to 1.44, still an overlap.

So the next value used is 1.5 - giving a range of 1.2-1.8
Next value? 2.2 - range of 1.76 (1.8 when rounded) to 2.64
Then 3.3 - 2.64 to 3.96
And so on

See the pattern?

Here is a list of available values for various tolerances.

So moral of the story - if your component is 3.3 @ 20% tolerance and you replace it with something 1% tolerance, don't be a gay and look for 3.3 if you have a 3.0 value available, because chances are the 3.3 @ 20% isn't 3.3 in the first place.

Or if you have a 3.0 @ 1% and you want to replace it with a 20% part, don't be gay trying to find a 3.0 @ 20% because you'll never be able to find it, and if you use 3 x 1.0 @ 20% it won't be precise anyway.

In short, just don't be gay.

But there are many opportunities for one to be gay. Like typing this blog. It's hard to cover all.

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