Obtaining E24 5% Resistor values from E6 5% Resistors.

[Jebnor]

I was looking into how best to optimize my resistor values.  I would love to have an entire kit of E24 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.

Requiv	E24	R1	R2	%err
100	100	100	-1	0.00
110	110	220	220	-0.00
110	120	220	220	-8.33
150	130	220	470	15.27
150	150	220	470	-0.10
150	160	220	470	-6.34
180	180	220	1000	0.18
200	200	220	2200	-0.00
220	220	220	-1	0.00
235	240	470	470	-2.08
235	270	470	470	-12.96
320	300	470	1000	6.58
320	330	470	1000	-3.11
387	360	470	2200	7.57
387	390	470	2200	-0.70
427	430	470	4700	-0.63
470	470	470	-1	0.00
500	510	1000	1000	-1.96
500	560	1000	1000	-10.71
688	620	1000	2200	10.89
688	680	1000	2200	1.10
688	750	1000	2200	-8.33
825	820	1000	4700	0.56
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.

Requiv	E24	R1	R2	%err
100	100	100	-1	0.00
110	110	220	220	-0.00
123	120	150	680	2.41
130	130	150	1000	0.33
150	150	150	-1	0.00
165	160	330	330	3.12
180	180	220	1000	0.18
200	200	220	2200	-0.00
220	220	220	-1	0.00
235	240	470	470	-2.08
270	270	330	1500	0.18
300	300	330	3300	-0.00
330	330	330	-1	0.00
358	360	470	1500	-0.59
387	390	470	2200	-0.70
427	430	470	4700	-0.63
470	470	470	-1	0.00
519	510	680	2200	1.85
564	560	680	3300	0.68
618	620	680	6800	-0.29
680	680	680	-1	0.00
750	750	1500	1500	-0.00
825	820	1000	4700	0.56
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.

[clifford]

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

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.

[Jebnor]

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. 

[Jebnor]

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.

[Zero999]

I made a spreadsheet awhile ago.

[edavid]

I was looking into how best to optimize my resistor values.  I would love to have an entire kit of E24 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.

[sleemanj]

See my paralleler:
  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.

[free_electron]

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.

[edavid]

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

[clifford]

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..

[clifford]

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)

[free_electron]

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

pff. i buy my e24 series in 1%. wikipedia schmikipedia...

[rsjsouza]

pff. i buy my e24 series in 1%. wikipedia schmikipedia...

There is a remark at the bottom of the table that mentions that...

[Zero999]

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.