for the HP 42S
LPFMF - Calculate voltage gain, center frequency and Q of a multiple-feedback low-pass-filter.

Multiple feedback low-pass-filter
Input
Resources to be used
Output

Program list
LPFMF - Rev.1.00 : Aug. 1 2011
00 { 164-Byte Prgm }
01 LBL "LPFMF"
02 MVAR "R1"
03 MVAR "R2"
04 MVAR "R3"
05 MVAR "C1"
06 MVAR "C2"
07 VARMENU "LPFMF"
08 STOP
09 EXITALL
10 RCL "R1"
11 1/X
12 RCL "R2"
13 1/X
14 RCL "R3"
15 1/X
16 +
17 +
18 1/X
19 RCL "C1"
20 RCL "C2"
21 RCL× "R2"
22 RCL× "R3"
23 ÷
24 SQRT
25 ×
26 STO "Q"
27 RCL "C1"
28 RCL× "C2"
29 RCL× "R2"
30 RCL× "R3"
31 SQRT
32 ENTER
33 +
34 PI
35 ×
36 1/X
37 STO "Fc"
38 RCL "R2"
39 RCL÷ "R1"
40 +/-
41 CLA
42 ENG 03
43 "Q="
44 ARCL "Q"
45 ", h="
46 ARCL ST X
47 "LFFc="
48 ARCL "Fc"
49 " [Hz] LPFMF"
50 AVIEW
51 RCL "Q"
52 RCL "Fc"
53 ENG 11
54 RTN
55 .END.

Example
Input
R1 = 30e3
R2 = 30e3
R3 = 15e3
C1 = 3e-9
C2 = 750e-12
Output
z: -1.0000000000E0
y: 707.106781187E-3
x: 5.00175731198E3

Download 'LPFMF-1.0' (lpfmf.raw, 167 byte, raw program file for the Free42)
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