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From: "karl AT aspodata DOT se [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To: geda-user AT delorie DOT com
Subject: [geda-user] combining resistors
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Message-Id: <20230407214542.03C6D8499AA8@turkos.aspodata.se>
Date: Fri,  7 Apr 2023 23:45:41 +0200 (CEST)
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Reply-To: geda-user AT delorie DOT com

  I have made a program that searches suitable values and combination
  to meet a goal value. It is called rfind.pl from:
https://aspodata.se/git/openhw/bin/

 Example useage:
a, You have 1% E6, 1k to 1M, resistors on self and need 23.9kOhm
 for a test:

$ rfind.pl min=1k max=1M E=E6 23.9k
 min   =    1.000 kOhm
 max   =    1.000 MOhm
  23.900k:
  err type     Rtot        R1        R2        R3
 7.95         22.000k:   22.000k 
 1.26  ser    24.200k:    2.200k   22.000k 
 1.67  par    23.500k:   47.000k   47.000k 
 0.42  ser    24.000k:    1.000k    1.000k   22.000k 
 0.16  par    23.939k:   33.000k  100.000k  680.000k 
 0.13  cb1    23.869k:   47.000k    1.500k   47.000k 
 0.06  cb2    23.886k:    4.700k   22.000k  150.000k 

So, I need at least 3 res. to get below 1% diff.

ser is all 2 or 3 res. in series
par is all 2 or 3 res. in paralell (||)
cb1 is R1 || (R2 R3 in series)
cb2 is R1 in series with (R2 || R3)

b, you need thin film 218k 0.1% 25ppm, sulphur resistant, but
 218k is only available in full rolls, and say you only need 10,
 and the series you are interesed in is only available in theese
 values from you favourite distributor:

 100, 150, 200, 220, 270, 330, 390, 470, 560, 1000, 1200, 1430,
 1910, 2400, 2490, 2700, 3240, 4020, 4300, 4700, 7500, 9100,
 9530, 11000, 13000, 15000, 20000, 22000, 24000, 24900,
 27000, 30000, 31600, 33000, 36000, 43000, 49900, 51000,
 75000, 82000, 100000, 110000, 120000, 150000, 160000,
 200000, 220000

 What combination should you use:

$ rfind.pl min=1k max=1M E=ERAV 218k
 min   =    1.000 kOhm
 max   =    1.000 MOhm
 218.000k:
  err type     Rtot        R1        R2        R3
 0.92        220.000k:  220.000k 
 0.92  ser   220.000k:   20.000k  200.000k 
49.54  par   110.000k:  220.000k  220.000k 
 0.00  ser   218.000k:   15.000k   43.000k  160.000k 
66.36  par    73.333k:  220.000k  220.000k  220.000k 
32.72  cb1   146.667k:  220.000k  220.000k  220.000k 
 0.00  cb2   218.000k:  200.000k   36.000k   36.000k 

 I'd choose 15k, 43k and 160k, or 200k, 36k and 36k.

Regards,
/Karl Hammar