(48) Closest Standard-Resistor Values
06-24-2019, 04:52 PM
Post: #1
 SlideRule Senior Member Posts: 826 Joined: Dec 2013
(48) Closest Standard-Resistor Values
An extract from “Calculator program finds closest standard-resistor values,” EDN magazine, Feb 3, 2005, pg 86.

You can use a Hewlett-Packard HP-48 or HP-49 calculator and one of the following programs written in RPN (Reverse-Polish Notation) to compute the nearest standard value that’s closest to a required value.You enter a required resistor value, and the program returns the closest higher or lower value in the selected series …

Listing 1: Convert a resistor value into the nearest value of the R24 series.
« ? r
« r MANT ? m
« {1. 1.1 1.2 1.3 1.5 1.6 1.8 2. 2.2 2.4 2.7 3. 3.3 3.6 3.9
4.3 4.7 5.1 5.6 6.2 6.8 7.5 8.2 9.1 10. } ‘L1’ ST0
0
DO
1 + DUP ‘L1’ SWAP GET UNTIL m >
END
DUP ‘L1’ SWAP GET m / ? b
« 1 – ‘L1’ SWAP GET m / INV ? a
« a b IF =
THEN r b * ELSE r a / END
-2 RND
» » » »
‘L1’ PURGE
»
***
Listing 2: Convert a resistor value into the nearest value of the R48 series
« ‘10^(1/48)’ ? r n ‘n^IP(LN(x*vn/LN(n))’ EVAL –3 RND »
***
Listing 3: Convert a resistor value into the nearest value of the R96 series.
« ‘10^(1/96)’ ? r n ‘n^IP(LN(x*vn/LN(n))’ EVAL –3 RND »

BEST!
SlideRule
06-26-2019, 11:00 PM
Post: #2
 John Keith Senior Member Posts: 425 Joined: Dec 2013
RE: (48) Closest Standard-Resistor Values
I saw that article years ago and thought the programs were very useful. I did not think that highly of the programming style of Listing 1 however and I took the liberty of rewriting it. I will now take the further liberty of posting my revision here. For HP-48G and later.

Code:
 \<< DUP MANT { 1. 1.1 1.2 1.3 1.5 1.6 1.8 2. 2.2 2.4 2.7 3. 3.3 3.6 3.9 4.3 4.7 5.1 5.6 6.2 6.8 7.5 8.2 9.1 10. } \-> r m L1   \<< L1 1.     \<< m >     \>> DOLIST 1. POS DUP 'L1' SWAP GET m / SWAP 1. - 'L1' SWAP GET m / INV DUP2 < { DROP r * } { SWAP DROP r SWAP / }  IFTE -2. RND   \>> \>>
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