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| Thread ID: 56664 | 2005-04-11 23:59:00 | XL Formula - (with a twist) | B.M. (505) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 343963 | 2005-04-12 03:45:00 | OK try this then www.p-m-services.co.uk A 77kb xls file or a 20kb zipped file. Ohms Law Spreadsheet Calculator. It was written using Microsoft Excel. As an added bonus it also includes the formula for calculating parallel resistor values. Looks like it calculates 5 resistors in parallel. |
Speedy Gonzales (78) | ||
| 343964 | 2005-04-12 03:57:00 | How often do you need to do this calculation? I've needed it about three times in the last five years. I just use whatever calculator is handiest. (Or a pencil and scrap of paper). ;) The most common requirement is to work out the values to obtain a non-preferred value,when a preset pot can't be used. Many years ago I used a FORTRAN programme to generate a table of the values needed to produce non-standard values. The original code was from a mainframe with 60 bit floating point. On the 48 bit Burroughs, I had to use double-precision to make it run. On a 32-bit PC you will need to watch for divide by zero errors. ;) |
Graham L (2) | ||
| 343965 | 2005-04-12 04:01:00 | If I am reading your example correctly, would something like this do it? =IF(ISBLANK(A1),0,1/A1) + IF(ISBLANK(B1),0,1/B1) + IF(ISBLANK(C1),0,1/C1) + IF(ISBLANK(D1),0,1/D1) etc etc Andrew :) |
andrew93 (249) | ||
| 343966 | 2005-04-12 04:11:00 | Thanks Speedy I’ll give that a go . In the meantime I’ve designed my own rather clumsy one, which I’ll have you know works a treat . All it took was for me to find my thinking cap, pour a large G&T and it was all over . (Maths from Cambridge High too) :lol: My trouble Graham is that I’m a bit reluctant to use my 1950’s Govt supplied HB pencil as there isn’t a lot of sharpening left in it! I’ll keep checking the mail box for my NZCEA and BAR . :) especially the BAR |
B.M. (505) | ||
| 343967 | 2005-04-12 04:34:00 | That would be much tidier than mine Andrew but unfortunately it gives the wrong answer. :) | B.M. (505) | ||
| 343968 | 2005-04-12 04:44:00 | Wouldn’t you know it Speedy, that site had exactly what I wanted. After I’d gone through the stress of designing my own. Anyway, I checked it against mine and they both produced the same answers so I happy about that. :) I tried to find their formulas but they’re well hidden somewhere. Tried every trick I know without success. Just wanted to compare our methods having compared the results. Thanks again Bob |
B.M. (505) | ||
| 343969 | 2005-04-12 05:31:00 | That would be much tidier than mine Andrew but unfortunately it gives the wrong answer. I was working with the example you provided but the point being you can test for null or nil values and build that into your formula. |
andrew93 (249) | ||
| 343970 | 2005-04-12 05:52:00 | Yep, I note that Andrew, but I cant coax it to give the right answer. :( Which by the way is 4.8ohms for a 10, 20, 30 & 40 ohm resistor in parallel. |
B.M. (505) | ||
| 343971 | 2005-04-12 06:05:00 | Try 1/((1/A1) + IF(ISBLANK(B1),0,1/B1) + IF(ISBLANK(C1),0,1/C1) + IF(ISBLANK(D1),0,1/D1)) - you must have at least one resistor (in cell A1 for the purposes of this formula). | andrew93 (249) | ||
| 343972 | 2005-04-12 06:32:00 | That's the one Andrew! Well done, and it's so much better than my efforts. Did you have a full bottle of Gin in front of you? :) |
B.M. (505) | ||
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