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Electronics => Beginners => Topic started by: Jebnor on September 05, 2013, 03:10:40 pm

Title: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: Jebnor on September 05, 2013, 03:10:40 pm
I was looking into how best to optimize my resistor values.  I would love to have an entire kit of E24 (http://www.logwell.com/tech/components/resistor_values.html) resistor values, but going from 10R to 4.7M is 5 1/2 decades at 24 per decade ...  132 different resistor values.   So I thought I would see what I can get away with. 


Starting with the E3 values (100,220,470) I wrote a program to exhaustively search all pairs of parallel resistors for value so see what could be obtained within the 5% tolerance of the resistors.
No dice...  Up to a 15% error on the 130 value.


RequivE24R1R2%err
   100   100    100     -10.00
   110   110    220    220-0.00
   110   120    220    220-8.33
   150   130    220    47015.27
   150   150    220    470-0.10
   150   160    220    470-6.34
   180   180    220   10000.18
   200   200    220   2200-0.00
   220   220    220     -10.00
   235   240    470    470-2.08
   235   270    470    470-12.96
   320   300    470   10006.58
   320   330    470   1000-3.11
   387   360    470   22007.57
   387   390    470   2200-0.70
   427   430    470   4700-0.63
   470   470    470     -10.00
   500   510   1000   1000-1.96
   500   560   1000   1000-10.71
   688   620   1000   220010.89
   688   680   1000   22001.10
   688   750   1000   2200-8.33
   825   820   1000   47000.56
   909   910   1000  10000-0.10
*note* a R2 value of -1, means you don't need it.  Just easier to compute with this 'invalid' number.


I bumped up to the E6 values.  Things are great, the biggest error is at the E24 value of 160, 3.12% error, within the 5% tolerance I was shooting for.
RequivE24R1R2%err
   100   100    100     -10.00
   110   110    220    220-0.00
   123   120    150    6802.41
   130   130    150   10000.33
   150   150    150     -10.00
   165   160    330    3303.12
   180   180    220   10000.18
   200   200    220   2200-0.00
   220   220    220     -10.00
   235   240    470    470-2.08
   270   270    330   15000.18
   300   300    330   3300-0.00
   330   330    330     -10.00
   358   360    470   1500-0.59
   387   390    470   2200-0.70
   427   430    470   4700-0.63
   470   470    470     -10.00
   519   510    680   22001.85
   564   560    680   33000.68
   618   620    680   6800-0.29
   680   680    680     -10.00
   750   750   1500   1500-0.00
   825   820   1000   47000.56
   909   910   1000  10000-0.10

Why not more in parallel to get more?  Or parallel/series combinations?  I could, but I would like to keep this to a chart I can tape to the workbench.

As for laying out PCB's with these values,  Surface mount components already have this problem solved, Just stack R1 and R2 on top of each other. ( I've seen this done, but I don't work in surface mount. If it's wrong please correct me.)  For through hole, I can give all my E24 values the same footprint and only populate one resistor on the E6 values. I expect this will make layout simpler, as everything is consistent no matter the resistor value chosen.

The footprint is just a .400 and .500 footprint merged.  The intent is to have one resistor stacked on the other, so, one value is on the inner .400 spacing, the other is on top using the outer .500 spacing.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: clifford on September 05, 2013, 03:30:25 pm
A couple of years ago I wrote a simple JavaScript program (tested in Firefox and Google Chrome) that gives you combinations of up to three E6 resistors to create any user-defined resistance:

http://svn.clifford.at/tools/trunk/electrotools/rcalc.html (http://svn.clifford.at/tools/trunk/electrotools/rcalc.html)

Just enter the value you need and click on "Evaluate".

Per default only the best match for one , two, and three resistors is displayed. Select "By circuit topology" in the drop-down menu to display all topologies considered by the tool.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: Jebnor on September 05, 2013, 03:37:29 pm
Quote from: clifford on September 05, 2013, 03:30:25 pm
http://svn.clifford.at/tools/trunk/electrotools/rcalc.html (http://svn.clifford.at/tools/trunk/electrotools/rcalc.html)

Just enter the value you need and click on "Evaluate".

Per default only the best match for one , two, and three resistors is displayed. Select "By circuit topology" in the drop-down menu to display all topologies considered by the tool.

Very nice, I'll bookmark that for future use. 
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: Jebnor on September 05, 2013, 03:47:59 pm
Quote from: clifford on September 05, 2013, 03:30:25 pm
http://svn.clifford.at/tools/trunk/electrotools/rcalc.html (http://svn.clifford.at/tools/trunk/electrotools/rcalc.html)

I think I found a bug.   If you enter "72.14k" and "By Circuit Topology" you get
Code: [Select]
Tripple Serial Resistor:
R_1 = 10 kOhm
R_2 = 15 kOhm
R_3 = 15 kOhm
R_min = 71.280 kOhm 
R_max = 72.720 kOhm
tolerance = 1.19%
Perhaps it's an artifact of display, but if memory serves, 10+15+15=40.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: Zero999 on September 05, 2013, 10:24:17 pm
I made a spreadsheet awhile ago.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: edavid on September 05, 2013, 11:35:26 pm
Quote from: Jebnor on September 05, 2013, 03:10:40 pm
I was looking into how best to optimize my resistor values.  I would love to have an entire kit of E24 (http://www.logwell.com/tech/components/resistor_values.html) resistor values, but going from 10R to 4.7M is 5 1/2 decades at 24 per decade ...  132 different resistor values.

I bought a kit of 10 each of 170 E24 values (1/4W 1% through hole metal film, 1R to 10M) for $17, and it fits in a small plastic bag.  Sometimes I love eBay.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: sleemanj on September 05, 2013, 11:45:02 pm
See my paralleler:
  http://sparks.gogo.co.nz/resistor_paralleler.html (http://sparks.gogo.co.nz/resistor_paralleler.html)
just scroll down to the "Your Resistor Stock List" section and configure it with the resistors you (will) stock, then you can select 2 as the max and hit search.

I wrote it because I never found a paralleler which only worked based on partial sets of resistors you have in stock, they all assumed you have a full set.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: free_electron on September 06, 2013, 12:07:50 am
small detail... E24 is 1% ... ain;t gonna get that with your 5% resistors... the software will get you close and then you will have to measure where you are.
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: edavid on September 06, 2013, 01:27:19 am
Quote from: free_electron on September 06, 2013, 12:07:50 am
small detail... E24 is 1% ... ain;t gonna get that with your 5% resistors... the software will get you close and then you will have to measure where you are.

Actually, E24 is 5%, E96 is 1%:

http://en.wikipedia.org/wiki/E24_series#E_series (http://en.wikipedia.org/wiki/E24_series#E_series)
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: clifford on September 06, 2013, 04:51:38 am
Quote from: Jebnor on September 05, 2013, 03:47:59 pm
Quote from: clifford on September 05, 2013, 03:30:25 pm
http://svn.clifford.at/tools/trunk/electrotools/rcalc.html (http://svn.clifford.at/tools/trunk/electrotools/rcalc.html)

I think I found a bug.   If you enter "72.14k" and "By Circuit Topology" you get
Code: [Select]
Tripple Serial Resistor:
R_1 = 10 kOhm
R_2 = 15 kOhm
R_3 = 15 kOhm
R_min = 71.280 kOhm 
R_max = 72.720 kOhm
tolerance = 1.19%
Perhaps it's an artifact of display, but if memory serves, 10+15+15=40.

Thanks for reporting this! I can reproduce the bug and will have a look at it later today..
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: clifford on September 06, 2013, 07:08:56 am
Quote from: clifford on September 06, 2013, 04:51:38 am
Thanks for reporting this! I can reproduce the bug and will have a look at it later today..

fixed it. (it was a simple typo in the function that prints the results. for this topology it reported the value of r2 as value for r2 and r3)
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: free_electron on September 06, 2013, 05:25:26 pm
Quote from: edavid on September 06, 2013, 01:27:19 am
Quote from: free_electron on September 06, 2013, 12:07:50 am
small detail... E24 is 1% ... ain;t gonna get that with your 5% resistors... the software will get you close and then you will have to measure where you are.

Actually, E24 is 5%, E96 is 1%:

http://en.wikipedia.org/wiki/E24_series#E_series (http://en.wikipedia.org/wiki/E24_series#E_series)

pff. i buy my e24 series in 1%. wikipedia schmikipedia...
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: rsjsouza on September 06, 2013, 05:30:49 pm
Quote from: free_electron on September 06, 2013, 05:25:26 pm
pff. i buy my e24 series in 1%. wikipedia schmikipedia...

There is a remark at the bottom of the table that mentions that...
Title: Re: Obtaining E24 5% Resistor values from E6 5% Resistors.
Post by: Zero999 on September 07, 2013, 05:34:01 pm
Of course you can buy 1% resistors in the E24 series. It's just that the nearest E24 number will always be within 5% tolerance of a particular value. You can also buy 0.5% values in E48 values.