HP 15C - LC resonator replacement for triple speed 15C
hp15c-0.jpg
Takayuki HOSODA
Oct. 12 2009
Japanese Japanese edition is here.

Triple speed modification (#2614A06612)

Internal view of the original HP 15C (Serial#=2614A06612, CPU=1LM2-0001)

Power supply current (Ta=26°C, Vbattery=4.72V(SR44×3), fLC=884kHz(original))
Internal view of the modified HP 15C (Serial#=2614A06612, CPU=1LM2-0001)

Parts replacement Parts addition


LC resonant frequency of the LC resonator
L : Inductance    [μH]
f0 : Self resonant frequency     [MHz]
fm : L,Q measurement frequency (fm   [MHz]
Qm : Quality factor at fm    
Rs : Equivalent series resistance (at Fm) ≈     [Ω]
Cp : Parallel capacitance     [pF]
fr : Resonant frequency ≈     [MHz]
Qe : Estimated quality factor (at Fr) ≈    
Example of the electrical characteristics of the actual inductors
TDK, SMD Inductors For Signal Line(Wound) NLV Series NLV32
Inductance
(μH)
Inductance
tolerance
Q
min.
Test frequency L,Q
(MHz)
Self-resontant frequency
(MHz)min.
DC resistance
(Ω)max.
Rated current
(mA)max.
Part No.
47 ±5% 30 2.52 15 7 60 NLV32T-470J
180 ±5% 20 0.796 7 17 60 NLV32T-181J

API Delevan, RF Inductors - Surface Mount - Shielded Surface Mount Inductors S1812 & S1812R Series
Inductance
(μH)
Inductance
tolerance
Q
min.
Test frequency L,Q
(MHz)
Self-resontant frequency
(MHz)min.
DC resistance
(Ω)max.
Rated current
(mA)max.
Part No.
47 ±10% 30 2.5 9 3.40 242 S1812R-473K
180 ±10% 40 0.79 4.5 8.50 153 S1812R-184K
  • Cbypass=22μF/10V/Ta → 100μF/6.3V (Murata, GRM31CR60J107ME39L), X5R, 3216M Large capacitance MLCC(Multi layer ceramic capacitor) is used for
    low impedance over wide temparature and frequency range for good bypassing,
    high capacitance for battery backup time at the stand-by current that might increase,
    and very low leakage current for long stand-by time. Parts addition
    Results (Ta=27°C, Vbattery=4.7V, fLC)
    Power supply current (Ta=27°C, Vbattery=4.5V(SR44×3), fLC=2.8MHz) Leakage current and Forward voltage of the protection diode
    DUT = BAT43, Ir ≈ 40 nA (Ta = 21 °C, Vr = 5 V), Vf ≈ 304mV (Ta = 21 °C, If = 2 mA)

    Triple speed modification (#2813A62318)

    Internal view of the original HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

    Internal view of the modified HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

    Parts replacement Parts addition
    Results (Ta=27°C, Vbattery=4.76V, fLC)

    Experimental modification for quad-speed 15C (#2813A62318)

    Internal view of the modified HP 15C (Serial#=2813A62318, CPU=1LM2-0001)

    Parts replacement Parts addition
    The self-diagnostics-test ([ON]+[×]) results at various voltage and LC conbination, and N-queens benchmark results.
    Ta=27°C Osillator inductor and capacitor Comment
    47μH, 47pF 47μH, 33pF 47μH, 27pF
    Vbattery IbatteryResult IbatteryResult IbatteryResult
    4.7V 2.9mAO.K. 3.2mAO.K. 3.4mAO.K. Nominal voltage of SR44×3 at 20°C
    3.8V 2.1mAO.K. 2.4mAO.K. 2.5mAO.K. Cut-off voltage of SR44×3 at -10°C
    3.6V 2.0mAO.K. 2.2mAO.K. 2.5mAO.K. -
    3.5V 1.9mAO.K. 2.1mAO.K. 2.2mAO.K. Low battery indicator turns on when
    Vbattery ≤ 3.5V
    3.4V 1.9mAO.K. 2.0mAO.K. -FAIL
    3.3V 1.8mAO.K. -FAIL -FAIL
    3.2V 1.7mAO.K. -FAIL -FAIL
    3.1V 1.6mAO.K. -FAIL -FAIL
    3.0V -FAIL -FAIL -FAIL
    2.7V
    Cut-off voltage of LR44×3 at 20°C
    tN-queens 23m15s 20m30s 19m25s Vbattery=4.7V, Ta=27°C

    Conclusion

    The triple-speed-modified HP-15C with 1LM2 processor seems works well, and stable as far as you are using SR44 (Zink Silver Oxide) batteries.
    The recommended parts value for the LC resonator are 47μH and 68pF so far.
    At least one bypassing MLCC (Multi Layer Ceramic Capacitor) of its value from 1μF to 10μF should be added to the power line for stable operation.
    DISCLAIMER
    These modifications are experimental, and the results should NOT be considered guranteed.
    The descriptions of the modifications herein does NOT imply endorsement or recommendation by the author.

    SEE ALSO

    REFERENCE


    APPENDIX - Program library


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