Obtaining E24 5% Resistor values from E6 5% Resistors. - Page 1
Forum section: electronics / beginners

author: Jebnor
author_rank: Regular Contributor
timestamp: September 05, 2013, 03:10:40 pm
content: I was looking into how best to optimize my resistor values. I would love to have an entire kit ofE24resistor 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%err100100100-10.00110110220220-0.00110120220220-8.3315013022047015.27150150220470-0.10150160220470-6.3418018022010000.182002002202200-0.00220220220-10.00235240470470-2.08235270470470-12.9632030047010006.583203304701000-3.1138736047022007.573873904702200-0.704274304704700-0.63470470470-10.0050051010001000-1.9650056010001000-10.716886201000220010.89688680100022001.1068875010002200-8.33825820100047000.56909910100010000-0.10*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%err100100100-10.00110110220220-0.001231201506802.4113013015010000.33150150150-10.001651603303303.1218018022010000.182002002202200-0.00220220220-10.00235240470470-2.0827027033015000.183003003303300-0.00330330330-10.003583604701500-0.593873904702200-0.704274304704700-0.63470470470-10.0051951068022001.8556456068033000.686186206806800-0.29680680680-10.0075075015001500-0.00825820100047000.56909910100010000-0.10Why 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.

author: clifford
author_rank: Regular Contributor
timestamp: September 05, 2013, 03:30:25 pm
content: 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.htmlJust 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.

author: Jebnor
author_rank: Regular Contributor
timestamp: September 05, 2013, 03:37:29 pm
content: Quote from: clifford on September 05, 2013, 03:30:25 pmVery nice, I'll bookmark that for future use.

author: Jebnor
author_rank: Regular Contributor
timestamp: September 05, 2013, 03:47:59 pm
content: Quote from: clifford on September 05, 2013, 03:30:25 pmI think I found a bug. If you enter "72.14k" and "By Circuit Topology" you getCode:Tripple Serial Resistor:R_1 = 10 kOhmR_2 = 15 kOhmR_3 = 15 kOhmR_min = 71.280 kOhmR_max = 72.720 kOhmtolerance = 1.19%Perhaps it's an artifact of display, but if memory serves, 10+15+15=40.

author: Zero999
author_rank: Super Contributor
timestamp: September 05, 2013, 10:24:17 pm
content: I made a spreadsheet awhile ago.

author: edavid
author_rank: Super Contributor
timestamp: September 05, 2013, 11:35:26 pm
content: Quote from: Jebnor on September 05, 2013, 03:10:40 pmI 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.

author: sleemanj
author_rank: Super Contributor
timestamp: September 05, 2013, 11:45:02 pm
content: See my paralleler:http://sparks.gogo.co.nz/resistor_paralleler.htmljust 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.

author: free_electron
author_rank: Super Contributor
timestamp: September 06, 2013, 12:07:50 am
content: 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.

author: edavid
author_rank: Super Contributor
timestamp: September 06, 2013, 01:27:19 am
content: Quote from: free_electron on September 06, 2013, 12:07:50 amActually, E24 is 5%, E96 is 1%:http://en.wikipedia.org/wiki/E24_series#E_series

author: clifford
author_rank: Regular Contributor
timestamp: September 06, 2013, 04:51:38 am
content: Quote from: Jebnor on September 05, 2013, 03:47:59 pmThanks for reporting this! I can reproduce the bug and will have a look at it later today..

author: clifford
author_rank: Regular Contributor
timestamp: September 06, 2013, 07:08:56 am
content: Quote from: clifford on September 06, 2013, 04:51:38 amfixed 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)

author: free_electron
author_rank: Super Contributor
timestamp: September 06, 2013, 05:25:26 pm
content: Quote from: edavid on September 06, 2013, 01:27:19 ampff. i buy my e24 series in 1%. wikipedia schmikipedia...

author: rsjsouza
author_rank: Super Contributor
timestamp: September 06, 2013, 05:30:49 pm
content: Quote from: free_electron on September 06, 2013, 05:25:26 pmThere is a remark at the bottom of the table that mentions that...

author: Zero999
author_rank: Super Contributor
timestamp: September 07, 2013, 05:34:01 pm
content: 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.