HP 35S: Resistors in Series or Parallel (Portred from HP-33E)


Resistors in Series or Parallel

Source: HP-33E Student Engineering Applications, 1978

Original Calculator: HP-33S

Credit to Hewlett Packard Company

Ported to HP 35S by Eddie Shore, 10/10/2013

1. For each group of parallel or series resistors: press XEQ R.

2. At the Mode Prompt (INPUT M), enter 0 R/S for Parallel Resistors, 1 R/S for Series Resistors

3. Enter resistor values (assumed to be in Ohms) then press R/S.

4. To find the total, press XEQ R016.

5. Optional: Store the result in a variable for future use, as long is it not R.

Parallel Resistors: total resistance = 1/( 1/R1 + 1/R2 + ... )

Series Resistors: total resistance = R1 + R2 + ...

R001 LBL R
R002 0
R003 STO R
R004 SF 10 // press Left Shift, Flags, SF, decimal point, 0
R005 0=PAR 1=SER // equation
R006 PSE
R007 CF 10 // press Left Shift, Flags, CF, decimal point, 0
R009 R/S
R010 RCL M
R011 x=0?
R012 XEQ R024
R013 R-down
R014 STO+ R
R015 GTO R009

R016 RCL R // total resistance
R017 RCL M
R018 x=0?
R019 XEQ R024
R020 CLx
R021 STO M
R022 R-down
R023 RTN

R024 R-down
R025 1/x
R027 RTN



I don't quite see the point of the program. I ususally do this:

R1 1/x R2 1/x + 1/x

or on the WP34S:

R1 Enter R2 g ||

I am probably missing something...


It's interesting to see a (ported) program from 1978, thanks to Eddie. In those days programming a calculator was such a novelty that I think HP just wanted to show off the input/looping features at every opportunity. Of course, series resistances can be much more easily calculated by addition, and parallel by a much simpler program: LBL R 1/x x<>y 1/x + 1/x RTN. That was as true in 1978 as it is now.

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