1. ## Using resistors

I 'm making a ir receiver for which i found the schematics in the web . i need a resistor of a value i cant find can i add other resistor up to that value and if yes is there a polarity i should respect ?

2. basic electronics:

resistors in series (one after another):
R(total) = R(1) + R(2)

resistors in parallel (side by side, with their lead connected):
1/R(total) = 1/R(1) + 1/R(2)
or
R(total) = {R(1)*R(2)} / {R(1)+R(2)}

someone PLEASE correct me if im wrong.

also, the equations can be continnued for more than 2 resistors, although the second eq for the parallel gets pretty hairy. just use the first one (for parallel) and a calculator!! the series one is always easy.

oh, and the equations are switched for capacitors.

~mike

3. someone PLEASE correct me if im wrong.
you are correct.

resistors is parallel are strange things.

On another note does any one know a site with the chart to tell you what coloured bands you need for a particular resistance??

hornet

4. Originally posted by hornet
On another note does any one know a site with the chart to tell you what coloured bands you need for a particular resistance?
No but

0 = Black
1 = Brown
2 = Red
3 = Orange
4 = Yellow
5 = Green
6 = Blue
7 = Purple / Violet
8 = Grey or White (can't rember which but nobody uses 8)
9 = Grey or White (can't rember which but nobody uses 8)

The first 2 or 3 (depends on the resistor) colour bands are the first 2 0r 3 numbers in the value and the last band is the number of zeros.

I think an example might help

red red yellow would be 220000 ohms or 220k ohms
yellow purple black red would be 47000 ohms or 47k ohms

The odd colour on it's own normaly gold or silver is the tolerance, just ignor it.

I cann't rember which way round you read the colour bands, but one way makes sense and the other doesn't.

I hope that make sense, rather than confussing things.

Rob

PS. Does any one know which is 8 & which is 9

5. 8 grey
9 white

6. this calculator is pretty handy if you are working near a computer.

~mike

7. mp3z24,
Man, that calculator and that entire site, rocks!

I can't get over the stuff you can do with Java.

8. Solder a small pot, adjust it, then use a drop of superglue to permanetly fix it's value.

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