HP-41 Ohms Law Program

[Jeff Davis]

I have been writing a program to calculate the Ohm's Law Circle. Below is the program. There are three calculations possible for each category based on which two inputs are non zero when the program runs. I am very interested in any feedback as well as program improvements to make the program run smoother and faster.

Please let me know your thoughts.

Thanks, Jeff

 01*LBL "OL"

 02 FIX 4

 03 "P,E,R,I,QUIT"

 04 AVIEW

 05 GETKEY

 06 CLD

 07 GTO IND X

 08*LBL 24 "AMPS"

 09 XEQ 05

 10 XEQ 04

 11 XEQ 03

 12 X=0?

 13 GTO 01

 14 X<>Y

 15 X=0?

 16 GTO 02

 17 /

 18 GTO "I1"

 19*LBL 01

 20 RDN

 21 /

 22 SQRT

 23 GTO "I1"

 24*LBL 02

 25 RDN

 26 /

 27*LBL "I1"

 28 "AMPS ="

 29 XEQ "VW"

 30 RTN

 31*LBL 52 "Ohms"

 32 XEQ 05

 33 XEQ 03

 34 XEQ 06

 35 X=0?

 36 GTO 01

 37 X<>Y

 38 X=0?

 39 GTO 02

 40 X<>Y

 41 /

 42 GTO "R1"

 43*LBL 01

 44 X<>Y

 45 X^2

 46 X<>Y

 47 X<> Z

 48 /

 49 GTO "R1"

 50*LBL 01

 51 RDN

 52 X^2

 53 /

 54*LBL "R1"

 55 "OHMS ="

 56 XEQ "VW"

 57 RTN

 58*LBL 15 "Volts"

 59 XEQ 05

 60 XEQ 04

 61 XEQ 06

 62 X=0?

 63 GTO 01

 64 X<>Y

 65 X=0?

 66 GTO 02

 67 *

 68 GTO "E1"

 69*LBL 01

 70 RDN

 71 *

 72 SQRT

 73 GTO "E1"

 74*LBL 02

 75 RDN

 76 /

 77*LBL "E1"

 78 "VOLTS ="

 79 XEQ "VW"

 80 RTN

 81*LBL 43 "Watts"

 82 XEQ 03

 83 XEQ 04

 84 XEQ 06

 85 X=0?

 86 GTO 01

 87 X<>Y

 88 X=0?

 89 GTO 02

 90 X<>Y

 91 X^2

 92 *

 93 GTO "P1"

 94*LBL 01

 95 X<>Y

 96 X<> Z

 97 X^2

 98 X<>Y

 99 X<> Z

100 /

101 GTO "P1"

102*LBL 02

103 RDN

104 *

105*LBL "P1"

106 "WATTS ="

107 XEQ "VW"

108 RTN

109*LBL 03

110 "VOLTS ?"

111 PROMPT

112 RTN

113*LBL 04

114 "OHMS ?"

115 PROMPT

116 RTN

117*LBL 05

118 "WATTS ?"

119 PROMPT

120 RTN

121*LBL 06

122 "AMPS ?"

123 PROMPT

124 RTN

125*LBL 51

126 CLX

127 FIX 5

128 END

[designnut]

I wrote a simple program to enter the x value into the stack to fill the t repeating register, it can be used to clear the stack if X is zero, or to enter E into the t repeating register. Keying a resistor and dividing gives I, multiplying then gives EI=W.
keying I and dividing gives R. This seemed sufficient for me. Sam

[Namir]

I suggest that you design your program using the following labels for the input of values and the calculations of results:

label A --> Input P

label B --> Input E

label C --> Input I

label D --> Input R

label E --> Quit

label a --> Calculate P

label b --> Calculate E

label c --> Calculate I

label d --> Calculate R

label "OL" --> display "P E I R Q" menu above the keys A, B, C, D, and E

The program displays the "P E I R Q" menu before each set of calculations. You then proceed to enter any three values and calculate the fourth one. After you view the result, you press the R/S key and have the program jump back to the label "OL" to display the "P E I R Q". Pressing E tells the program to display a termination message like "DONE" or "BYE".

Namir

Edited: 25 Dec 2010, 4:13 a.m.

[Walter B]

If you want a widespread use and understanding please remember the common letter for voltage is U.

[Garth Wilson]

As someone who has been in electronics engineering in the U.S. for the last 25 years, I have never heard of using "U" for "voltage." Karl's link below seems to explain why: it's mostly only in use in Europe. I would not say it's in "widespread use" here.

Edited: 27 Dec 2010, 3:19 a.m.

[Karl Schneider]

Here's the post containing the link that Garth referred to:

Quote:

---

If you want a widespread use and understanding please remember the common letter for voltage is U.

---

I've wondered about this, having seen "U" utilized to denote 'voltage' (potential difference) in German and Scandinavian documents. "V" and "E" (electromotive force) are favored in North America, but I have not thought this to be ideal.

• "V" leads to circularities:

  What does it signify? 'Voltage'.
  
  How is that measured? Volts.
  
  How is the unit "volt" abbreviated? V.

• "E" can also denote the electric field (normally as a vector), or energy.
  

However, it also seems that use of "V" for denoting potential difference is not unique to North America. I found a short discussion from five years ago to be reasonable:

http://boards.straightdope.com/sdmb/archive/index.php/t-338522.html

I tried to verify it expediently by reviewing Wikipedia pages in a number of languages that concerned 'potential difference'. However, not having ready access to textbooks from around the world, I couldn't say if the explanation given in the discussion is entirely correct. Perhaps knowledgeable Forum'ers in Britain, Australia, Spain, Italy, France, Netherlands, and Brazil might like to chime in...

-- Karl

Edited: 27 Dec 2010, 3:05 a.m.

[Gerson W. Barbosa]

Quote:

---

• "V" leads to circularities:

  What does it signify? 'Voltage'.
  
  How is that measured? Volts.
  
  How is the unit "volt" abbreviated? V.
  

---

One of my textbooks (HAYT Jr, William H. & KEMMERLY, Jack E. Análise de Circuitos em Engenharia) uses v for voltage (and i for current). Thus, Ohm's Law is stated as

v = Ri

Also, this notation avoids ambiguity in expressions like v = 6 V. All my other engineering textbooks use uppercase V indistinctly for both voltage and the SI unit, however. Here, some high-school Physics textbooks use U for voltage.

Gerson (Brazil).

[Bart (UK)]

Certainly my experience in both South Africa and the UK is V for voltage.

Lowercase v & i are usually used for instantaneous values (e.g. in AC analysis).

[Walter B]

Just checked some Wikipedia articles in different languages:

Quote:

---

Le symbole normalisé d'une tension électrique est U.
Das Formelzeichen der Spannung ist U – abgeleitet vom lat. urgere (drängen, treiben, drücken).
Symbol veličiny: U
U = Diferença de potencial ou tensão (Volts).
Sähköinen jännite (tunnus U, lat. urgere, etenkin amerikkalaisessa tekstissä usein V), eli sähköinen potentiaaliero, kahden pisteen välillä määritellään varatun hiukkasen näiden pisteiden välillä valitsevan potentiaalienergiaeron ja hiukkasen varauksen suhteena.

---

The latter claims US-Americans use another letter than the international community - as usual ;)

[Les Bell]

Quote:

---

Just checked some Wikipedia articles in different languages:

The latter claims US-Americans use another letter than the international community - as usual ;)

---

As former editor of various international editions of an electronics magazine (in the UK, Canada and Australia) I've never seen U as a symbol for voltage. It's always been V or equally commonly E (for electromotive force, I believe).

One might more properly claim that some parts of Europe use a different letter from the international community - as usual ;)

Best,

--- Les

[http://www.lesbell.com.au]

[Karl Schneider]

From the "off-Forum" discussion of 2005 I linked, along with my limited personal experience, I took it as a given that potential difference or 'voltage' was denoted by "U" in the Germanic, Scandinavian, and eastern European countries. It also now seems clear that "V" remains the favored term in British-influenced countries (UK, USA, Canada, Australia, South Africa). But what about the prominent western and Mediterranean countries of Europe (France, Spain, Italy, and Portugal)?

A closer examination of pertinent Wikipedia pages in Romance languages suggests that "U" denotes electric potential difference, while "V" denotes electric potential, even though both have the same unit (volt).

At least three of the pages criticized the term 'voltage' in favor of 'tension' -- for the good reason of eliminating circularity of terminology, but 'tension' itself can also mean the physical, weight-bearing load that stresses an overhead electrical line.

Portugese:

Quote:

---

...voltagem está tecnicamente incorrecto, ... A maioria dos engenheiros eletricistas repudiam o uso do termo voltagem...

---

My interpretation: "...'voltage' is technically incorrect .. A majority of electrical engineers repudiate the use of the term 'voltage'..."

French:

Quote:

---

Elle est souvent nommée voltage par le grand public, mais ce terme n'est pas utilisé professionnellement car il s'agit d'un anglicisme.

---

My interpretation: "It is often popularly called 'voltage', but the term is not used professionally (as an) anglicism."

Italian:

Quote:

---

Sempre nell'ambito elettrico, tale differenza di potenziale è anche chiamata comunemente tensione o, più raramente (ed impropriamente), voltaggio.

---

(Help?) "... potential difference...'tension', (or the rarer) and improper 'voltage'."

-- Karl

Edited: 30 Dec 2010, 1:08 a.m. after one or more responses were posted

[Walter B]

Quote:

---

Quote:

---

Sempre nell'ambito elettrico, tale differenza di potenziale è anche chiamata comunemente tensione o, più raramente (ed impropriamente), voltaggio.

---

(Help?) "... potential difference...'tension', (or the rarer) and improper 'voltage'."

---

Interpretation Aid: "Always in the electrical area, this difference of potential is also commonly called 'tension' or, more rarely (and improperly), 'voltage'."
Watch out: This is not a "potential difference" = ambiguity of the English language. Please note there's an obvious difference between adjectives and adverbs, too :-/

Addendum 1:

Quote:

---

But what about the prominent western and Mediterranean countries of Europe (France, Spain, Italy, and Portugal)?

---

I hate to repeat, but as stated in my post you responded to, at least French and Portuguese use U. French even inform you (just for the case case you didn't know before) this U is the "standardized symbol" for electrical tension - please check the site of IEC - regards to Les ;)

Addendum 2:

Quote:

---

As former editor of various international editions of an electronics magazine (in the UK, Canada and Australia) ...

---

Please don't confuse "international" with "English speaking country" or "former British colony".

Edited: 28 Dec 2010, 6:08 a.m.

[Les Bell]

As a member of the IEEE, I have to defer to my ancient copy of the "Electronic Engineer's Handbook", Donald G. Fink (ed), McGraw-Hill, 1975. Para 1.27 states:

Quote:

---

Electrostatic Potential and Potential Difference.
[...] While it is not possible to specify uniquely the absolute potential of any point in an electric field, the difference in potential between two points in the field can be determined when the manner in which the electric field strength varies between the points is known.

[...]

The potential difference between two points a and b in an electric field of strength E is, then

V_ab = . . .

---

I've omitted the rest of the equation - I wish the web and email spoke LaTeX, but it doesn't. ;) And for the rest of this 2.8"-thick (oops: 71mm-thick) book, so it goes - consistently using V to represent voltages (which we all know are potential differences). The word "tension" doesn't appear in the index, and disappeared from electrical English usage around the same time as vacuum tubes.

Now, to business:

Quote:

---

French even inform you (just for the case case you didn't know before) this U is the "standardized symbol" for electrical tension - please check the site of IEC - regards to Les ;)

---

Ah, yes - but if you look one line higher(http://www.iec.ch/zone/si/si_elecmag.htm#si_epo), you'll see:

Electric potential, V

Since you can't measure an absolute potential, there is no unit for it, and the SI unit, the volt, must represent a potential difference. So V and U are the same thing by different names, and the IEC should stick to what it's good at: setting standards for power supply connectors. ;)

Quote:

---

Please don't confuse "international" with "English speaking country" or "former British colony".

---

We had French and (it's been so long I can't remember) either Dutch or German editions as well - and in my occasional communications with them I can't recall "U" being used. I certainly never received any requests to explain our use of "V", but I would certainly have been puzzled if I had seen "U = IR" in the copies of their editions that I occasionally browsed.

My advice is, in any calculator program which has to represent voltage and which you hope will be used internationally, stay away from "U". We all know what "V" is, even if we resent its imperialistic connotations. And for proof that "U" is confusing, just read this thread and those linked from it.

Of course, the prudent programmer will probably wish to determine the Mandarin/Chinese/Japanese character for voltage, since it will probably ultimately trump "V", "E" and "U". But since it probably isn't on the keyboard of the HP-41 (and since they probably use "V" anyway ;) ) I'd say you're safe for the time being. And besides, Alessandro Volta deserves the credit.

With tongue planted firmly in cheek,

--- Les

[http://www.lesbell.com.au]

[Massimo Gnerucci (Italy)]

Quote:

---

And besides, Alessandro Volta deserves the credit.

---

Just to firmly keep this tongue in cheek (and joking on Volta's translation into english):

NO U-TURN, PLEASE!



Greetings,
Massimo

[Thomas Klemm]

Quote:

---

I wish the web and email spoke LaTeX, but it doesn't. ;)

---

cf. How to use a formula in a post

[Les Bell]

Ooh - that's handy, Thomas! Thanks for the pointer.

Best,

--- Les

[http://www.lesbell.com.au]

[John B. Smitherman]

Quote:

---

Please don't confuse "international" with "English speaking country" or "former British colony".

---

Walter, I believe that Les' use of international is correct - between or among nations; involving two or more nations.

Regards,

John

[Walter B]

John, of course you're right. According to what was written above, however, it looked like a subset of "international" was used. If some editors publish their product in Austria, Switzerland and Germany, they may call it an "international magazine" rightfully, but hmmmh ... It seemed to me, Les' international editing was of a similar kind ;)

[Les Bell]

Well, the magazine was called "Electronics Today International". . .

Best,

--- Les

[http://www.lesbell.com.au]

[Walter B]

Names and titles are all hollow words d;-)

[Gerson W. Barbosa]

Quote:

---

Lowercase v & i are usually used for instantaneous values (e.g. in AC analysis).

---

You're right! That's exactly what the authors say in the first chapter of the book (Definitions and Units). It's been quite a long time since I last read it, but I do remember my HP-28S was particularly useful then :-)

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv015.cgi?read=82010

Regards,

Gerson.

[Dieter]

Hehe... for decades this kind of calculation has been a classic
for any programmable calculator: a set of variables, connected
by a set of equations - enter some of them and determine the rest.



For this kind of program I prefer the same approach other HPs use for their TVM calculations: Every variable is assigned to a certain key. Enter the known values in any order, then have the program determine the others, again in any order you like.



I usually did it this way:



- Every variable uses its dedicated key. The self-assigning
alpha-labels may be used. In this case for instance

• [A] = voltage (Volts)
  
• [B] = resistance (Ohms)
  
• [C] = current (Amperes)
  
• [D] = power (Watts)
  
  
• [E] = Initialisation
  

- Pressing a key *either* enters this value *or* starts its calculation. This is usually done by checking Flag 22 (data entry). Or the program may check whether the input is zero (start calculation) or not (data entry).



- The program knows which variables have been entered and therefore
which others will have to be calculated in which way. This can be done with a simple trick: think of the four variables as bits in a four-digit binary number. So 1001 means that the first and the fourth variable have been entered, and 0110 means the second and third one are known. Each time a variable is entered, the program sets its corresponding bit by adding the respective decimal value, adding up to a unique "variable code":

• Add 1 when U (voltage) is entered
  
• Add 2 when R (resistance) is entered
  
• Add 4 when I (current) is entered
  
• Add 8 when P (power) is entered
  

In this case (Ohm's law) always two values are known and the two others can be calculated. So we end up with six possible cases, resulting in six different variable codes: 3, 5, 6, 9, 10 and 12.

The rest is easy: a simple indirect jump to label 03, 05, 06, 09, 10 or 12 where the two remaining values are evaluated and stored. For instance, at label 06 the values for R and I are known, so the missing voltage is determined by U = R*I and the unknown power is P = U*I.



I think most of us who are familiar with the HP41 will be able to
write such a program whithout major effort. My solution works
as described above, for example with U = 24 V and R = 470 Ohms:



Initialize

   XEQ "OHM"

Enter values U and R:

   24  XEQ A

   470 XEQ B

Now any key A, B, C or D can be pressed to get the corresponding value:

    XEQ C   =>  I=0,051

    XEQ D   =>  P=1,226

All other values can be recalled as well:

    XEQ A   =>  U=24,000

    XEQ B   =>  R=470,000

I do not include the listing - I think it's trivial.



Dieter

[Nigel Bamber]

Quote:

---

Hehe... for decades this kind of calculation has been a classic
for any programmable calculator: a set of variables, connected
by a set of equations - enter some of them and determine the rest.



For this kind of program I prefer the same approach other HPs use for their TVM calculations: Every variable is assigned to a certain key. Enter the known values in any order, then have the program determine the others, again in any order you like.



I usually did it this way:



- Every variable uses its dedicated key. The self-assigning
alpha-labels may be used. In this case for instance

• [A] = voltage (Volts)
  
• [B] = resistance (Ohms)
  
• [C] = current (Amperes)
  
• [D] = power (Watts)
  
  
• [E] = Initialisation
  

- Pressing a key *either* enters this value *or* starts its calculation. This is usually done by checking Flag 22 (data entry). Or the program may check whether the input is zero (start calculation) or not (data entry).



- The program knows which variables have been entered and therefore
which others will have to be calculated in which way. This can be done with a simple trick: think of the four variables as bits in a four-digit binary number. So 1001 means that the first and the fourth variable have been entered, and 0110 means the second and third one are known. Each time a variable is entered, the program sets its corresponding bit by adding the respective decimal value, adding up to a unique "variable code":

• Add 1 when U (voltage) is entered
  
• Add 2 when R (resistance) is entered
  
• Add 4 when I (current) is entered
  
• Add 8 when P (power) is entered
  

In this case (Ohm's law) always two values are known and the two others can be calculated. So we end up with six possible cases, resulting in six different variable codes: 3, 5, 6, 9, 10 and 12.

The rest is easy: a simple indirect jump to label 03, 05, 06, 09, 10 or 12 where the two remaining values are evaluated and stored. For instance, at label 06 the values for R and I are known, so the missing voltage is determined by U = R*I and the unknown power is P = U*I.



I think most of us who are familiar with the HP41 will be able to
write such a program whithout major effort. My solution works
as described above, for example with U = 24 V and R = 470 Ohms:



Initialize

   XEQ "OHM"

Enter values U and R:

   24  XEQ A

   470 XEQ B

Now any key A, B, C or D can be pressed to get the corresponding value:

    XEQ C   =>  I=0,051

    XEQ D   =>  P=1,226

All other values can be recalled as well:

    XEQ A   =>  U=24,000

    XEQ B   =>  R=470,000

I do not include the listing - I think it's trivial.



Dieter

---

[Nigel Bamber]

Quote:

---

I do not include the listing - I think it's trivial.

---

Not to me it isn't!

What an elegant solution. If you have it can you share it ?

Thanks

Nigel

[Thomas Klemm]

cf. Ohm's Law for the HP-41C/CV/CX

If you don't have a card reader you can replace the following command with CL (clear sigma) and set REG 21:

112 7CLREG

Switch to USER mode and use the following key-mapping:

• [A] = Initialisation
  
• [B] = P (power)
  
• [C] = I (current)
  
• [D] = U (voltage)
  
• [E] = R (resistance)
  

Initialize

   XEQ A

Enter values U and R:

   24  XEQ D

   470 XEQ E

Now any key B, C, D or E can be pressed to get the corresponding value:

    XEQ C   =>  I=0.051

    XEQ B   =>  P=1.226

All other values can be recalled as well:

    XEQ D   =>  U=24.000

    XEQ E   =>  R=470.000

The program doesn't use Dieter's method but instead calculates the value if it is 0. Feel free to modify it to your needs.

Cheers

Thomas

Edited: 2 Jan 2011, 1:24 p.m.

[Dieter]

I used this method about twenty years ago for a triangle calculation program: three sides and three angles are six variables, three of which are given by the user. That's eighteen possible combinations, and here the mentioned method starts making sense.



In this much simpler four-variable-case it gets even more elegant with another method I'm experimenting with at the moment: The 41 has these nice four flag indicators for flags 1 to 4. So the user can see how many and which values were entered. Using four flags instead of four binary digits (1, 2, 4 and 8) also has another advantage: Enter two values, determine the other two by simply pressing the respective key, then change one of the values (or enter a third one), or even remove one, and see how the other values change correspondingly.



Example: Enter U = 24 V and R = 470 Ohms to get I = 0,051 A and P = 1,226 W. Then change P to 1 Watt and see that R now is 576 Ohms. So far so good.

Now change R to 560 Ohms, try to determine I and get an error message since the now three given values U, R and P do not match.

Remove U and recalculate it, giving U = 23,664 V and I = 0,042 A.



I'm working on it. :-)



Dieter

[Thomas Klemm]

I guess this is how Sam would solve these problems:

Quote:

---

Example: Enter U = 24 V and R = 470 Ohms to get I = 0,051 A and P = 1,226 W.

---

24   ENTER   ENTER   ENTER          24.000

470   /                              0.051

*                                    1.226

Quote:

---

Then change P to 1 Watt and see that R now is 576 Ohms. So far so good.

---

CLx   1   /   *                    576.000

Quote:

---

Now change R to 560 Ohms (...)
Remove U and recalculate it, giving U = 23,664 V and I = 0,042 A.

---

1   ENTER   ENTER   ENTER            1.000

560   *   SQRT                      23.664

/                                    0.042

---

cf. EE calculations, some not obvious

Ohm's law

This may seem simple, but can be used as a rapid verification of dissipation and the voltage and current relation. Remember the little circles of voltage E divided by the IR product.

Key in the voltage repeatedly, and divide by either I or R to see the other value, as in E=IR.

The power in a resistor can be found by keying in the resistor and dividing to get I, then multiplying to get EI. It can be used to solve W=EI, by keying in power repeatedly, and dividing to get either E or I.

---

Sam, it's a pity your article is hard to read. I think it's a treasure unfortunately well hidden. Above you may find a suggestion to improve its legibility. Add some examples if possible and maybe some explanations or pictures as well.

Best regards

Thomas

[Ren]

For a technoclutz like me,
does this HP-41 listing
work with an HP-48G?

@Walter,
As I've previously noted you and I pronounce (some?) letters of the alphabet differently, U = voltage?
Maybe your "u"'s sound like my my "v"'s or vice-versa "woltage",
wice-wersa (typed purely in jest, no offense intended)

Ren

[Walter B]

Hi Ren,

dona nobis pacem ;) FYI, AFAIK the letter U employed for voltage has no relation with any pronounciation. It's just a letter commonly used for this physical entity like I is common for the current, L for inductivities etc. And as Karl mentioned, a capital V would be ambiguous, as well as a capital E is since it's employed for the electrical field strength.

Referring to the point you brought up: I dunno where you come from nor live, though the probability for being US-American is pretty elevated in this forum. Since I am definitely no native English speaker I will certainly make some pronounciation errors (among others), though following some decades of experience people in "English" speaking countries understand me quite well (allowing me leading some projects there) - far better than most "English" speakers are understood here (if they bother learning a second language at all).

Since you know "languages" is one of my hobbies, you know there's no offense intended. BTW, is your forum name in any way connected to the Chinese word for man?

[Ren]

@Walter B.,

I am in Southeastern Minnesota, USA, while I'm not fluent in any other language than English, I have had limited learning experience in Spanish, Arabic, and Chinese Mandarin, which brings me to your question on my name.

I was named after a friend of my dad's, he died in a rodeo while I was very young, so I'm not sure if I ever met him, and never asked him where our name came from. It has been suggested it came from (Saint) Irenaeus.

One of my Mandarin teachers in giving me a Chinese name used the word "kindness" (also pronounced "ren")

[Thomas Klemm]

Quote:

---

does this HP-41 listing work with an HP-48G?

---

With an HP-48G I'd recommend to use the built-in equation library:

2: Electricity

2: Ohm's Law and Power

Or you could install the HP-41E MicroCode Emulator and use the listing.

Cheers

Thomas

[designnut]

I admit I felt sad when I first saw a fellow using a programmable calculator for Ohms law.If one can't solve that simple a problem do they really belong in electrical engineering? What happens when you get a hard problem? Panic city? Sam

[Martin Pinckney]

Ouch, Sam!

Though a CE, not an EE, I have written solver routines for similarly simple relations, like the Rational Formula (Q=CiA). For me , its not the difficulty of the problem, its the convenience when doing repetitious calculations that makes these programs useful, particularly when you have the variable names displayed in front of you.

[Jeff Davis]

Thanks to all who have responded. I am not an EE but I do like to program on the HP-41. Since I was currently in a project to calculate a few items I thought it would be fun to write a program. I know it is trivial but fun none the less.

[Ren]

@Sam

Touche'!

In my defense, I was thinking about the "harder to memorize" (for me) equations of Ohm's Law. (Please forgive my lack of HP calculator notation in these examples)

i.e.

Square root(Power divided by Resistance) equals Inductance

or

E (or U, or V) equals Square root (Power times Resistance)

or

E(squared) divided by R equals P

While many subscribers to this forum could probably derive the above examples in their head (knowing that P=IxE and P=I(squared)R,
it took me several minutes to work the last one out on paper!

Ren

dona nobis pacem

[designnut]

What I suggest to calculator users for frequently encountered problem is to think about kepstroke procedures rather tthan formulas. There is a kinesthetic sense that can work for you in rapid solutions. Formulas are handed down from generation to generation with no reference to current circumstances.
Since the calulator is in everyday use, you must revise your formulas to be useful in the calculator. I solved one resistive divider until I knew all the answers. I played with the soluion and a solution that was usually awkward appeared. I retraced my steps. found the solution easy and tested it for other cases and found it accuate. It is a keystroke solution which has no equivalent in published equations. Here it is: for a resistive divider enter the lower resistor repeatedly to fill the t regtister. Key the upper resistor and add, see the total resistrance, divide and see the divider voltage fraction. Multiply and sutracct and the Thevenin soue resistance of thee divider appears. steps, add, divide, multiply, sutions. so take the book formuas and turn them into procedures useful to you on the keyboard. To be ccontinus. sam

[designnut]

Sorry, my writing kept disappearing on me. The steps are Add, divide, multiply, subtract and the equivalent output resistance appears. when doing RC frwequency corners tthe formulas were
R=Xc=1/2(Pi)FC. I changed thatt to 2(Pi)FRC=1, simply multiply the known factors together and invert to find the missing value. Again you can run 2Pi up the stack so it is available repeatedly.

[Ren]

Good advice Sam!

Thanks!

Ren

dona nobis pacem

[Martin Pinckney]

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What I suggest to calculator users for frequently encountered problem is to think about keystroke procedures rather than formulas. There is a kinesthetic sense that can work for you in rapid solutions.

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Well, I think I understand this, although I [did not] completely follow your examples.

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Formulas are handed down from generation to generation with no reference to current circumstances.

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Not sure what you mean by this. The formulas we have been discussing are expressions of physical laws that don't change. I see no reason that relations published in textbooks should be revised for particular calculator styles. They are sometimes rewritten in calculator manuals, though.

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Since the calculator is in everyday use, you must revise your formulas to be useful in the calculator.

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Perhaps yes, for RPN calculators. No doubt when you started out with the early HP's, this made sense. And still may for some people. But the original RPN HP's were developed when memory resources (RAM and ROM) were very expensive. Now there are lots of choices in calculator styles, many of which allow easy evaluation of the formulas in the original form, which makes more sense to some people. This is why we have choices in calculators.

Edited to correct meaning.

Edited: 31 Dec 2010, 10:14 a.m. after one or more responses were posted

[designnut]

Martin, I have discovered relations that have not been shown in formulas. They were exposed by the handy number manipulation of the calculator. I suggest it is the difference between the academic approach (everything has been learned that can be learned) and the engineering approach where it is possible to discover something new and incorporate in the lessons. Not only are the formulas copied in content bu in form, however awkward it may be. Yet nothing new is added. Have we learned nothing in the years? I found formulas have not adapted to modern usage and are totally outmoded. I gave the example R=Xc=11/2(Pi)FC. How much handier is 2(Pi)FRC=1. The old form is still in use, copied from book to book. The resonance formula is always F=1/[2(Pi) (LC)]^1/2.
I squared it and moved all tthe terms to the left as [2(Pi)]^2LC=1.
Then I used the repeeating T register to store 2(Pi)F and solved by muiplying twice to square the term. I adapted the forrmula for rapid use with RPN. If you never use RPN you will not benefit from the change. I've read you use algebraic so you must use archaic formulas and do not benefit from modern methods.

[Martin Pinckney]

Sam,

I acknowledge that you have developed shortcuts that work well with RPN calculators that served you well in your career.

However, to describe these as "modern methods" seems curious to me. I remind you that the early HP calcs were originally designed with RPN because of the limitations of technology at the time. The "change" that occurred in calculator design has gone the other way, first to algebraic, then to textbook entry/display. I for one have benefited from this change.

I am not against RPN. I have and use several HP RPN calcs. I am only against presenting RPN as if it were this magical superior system that only the few know how good it is.

[designnut]

Martin, we don't need no stinkiin parentheses. I did find relations I have not seen addressed in books, I think if they were known they would be addressed. I discovered them only because of the handy number manipulation available with RPN. I believe they have not been shown because they have not been discovered. Possibly my investigation has been more exhaustive than formerly.
While the solution of formulas for any variable is available in calculators, first you muct call the formula and enter each known element and then solve. I find it more adroit to key the data in RPN and get direct solutions. I founnd RPN handy when one realized that a change of units was needed in mid-solution, handy with step by step solution. Also it enables one to sense when one is making a mistake, and mentally follow the calculation and back out an error and revover. I found using the repeating t register in solutions a key to speed and versatility. Sam

[Martin Pinckney]

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Martin, we don't need no stinkin' parentheses.

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I know. You've said that already. But sooner or later you will encounter a complex expression that you can't evaluate directly with RPN unless you use the storage registers. Which I can avoid with my stinkin' parentheses!

[Walter B]

Martin,

FYI, the little device shown in that other thread has 8 stack levels as a user settable alternative to traditional 4 levels. Based on several decades of real life experience, I tell you you'll *never* encounter a real formula requiring more than 6 levels. You can design one easily, of course, but it's not our task making life more complicated than it is.

[Martin Pinckney]

Walter,

Yes, but Sam probably used traditional 4-level HP's.

[Ren]

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With an HP-48G I'd recommend to use the built-in equation library:

2: Electricity

2: Ohm's Law and Power

Cheers

Thomas

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Doh!

B^)

Ren

dona nobis pacem