calculator for resistive divider using standard resistor values?

Spreadsheet.

Cheers! Rich

"Ken Taylor" wrote in news:DiZqf.10243$vH5.499299 @news.xtra.co.nz:

Hello Ken,

Cool. I've always use a slide rule calculator for that. Well, maybe I'll keep doing that.

Regards, Joerg

Looks good - I'll hold on to that for the future. Thanks,

-M. No>

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Google. I actually used Altavista and used +resistor +combination

Cheers.

Ken

I once knocked up a C program that you are welcome to try, or perhaps expand on.

It has a very lazy algorithm that searches all combinations of 2 and 3 resistor dividers to find the closest match. You can customise the first line of main() to choose between e6, e12 or your own resistor value series. There are still plenty of configurations it does not try, such as three resistors in series. Also you have to get the correct power of 10 by yourself!

John

===============================================================

#include "stdio.h" #include "math.h"

/* The E12 series */

float e12_base[]= { 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 }; float e6_base[] = { 1.0, 1.5, 2.2, 3.3, 4.7, 6.8}; float my_base[] = { 1.0, 1.5, 1.8, 2.2, 4.7, 6.8};

/* program to find the optimum series-parallel combination of resistors, to get a given ratio */

float xyz1(float x, float y, float z) { return x/(1.0/(1.0/y+1.0/z)); }

float xyz2(float x, float y, float z) { return x/(y+z); }

int main(void) { /* customise these three (6 or 12) */ float * base_series=e12_base; int base_N=12;

int decades=6;

float target;

int N=base_N*decades; int x,y,z; float min_error=1E30; float error; float ratio; int x_min, y_min, z_min;

float series[N]; int i; float decade=1; int n=0; for(i=0;i

Oh well- forget it then!- waaaaa...ay too much thinking required....

:)

That's a bit restricted.

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

Misattributed, but I'll take any collateral accolades.

Ken

Yes, my interest was in getting as close as possible with a *limited* range of part values.

You can edit the program to put whatever sequence you like in. That's what the my_base array was for, just fill it in with E96 or whatever.

I wrote a javascript version a year of two ago:

Yes, at

Rene

TI had an Excel spreadsheet on their site a while ago. Its now a Javascript.

I'll send you the spreadsheet.

Dave F.