HP-15C - LC resonator replacement for triple speed 15C

HP 15C - LC resonator replacement for triple speed 15C

Takayuki HOSODA
Oct. 12 2009

Japanese edition is here.

Triple speed modification (#2614A06612)

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

Power supply current (T_a=26°C, V_battery=4.72V(SR44×3), f_LC=884kHz(original))

I_run≈1.2mA
I_idle≈27μA
I_standby<0.1μA
I_on-key≈2.7mA

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

Parts replacement

C_osc=180pF → 68pF/C0G (Kemet, C0805C680J5GACTU), 50V, 2012M
L_osc=180μH (R_s=5.5Ω) → 47μH (API Delevan, S1812R-473K), R_s= 3.5Ω, Shielded
C_bypass=22μF/10V/Ta → 100μF/6.3V (Murata, GRM31CR60J107ME39L), X5R, 3216M

Parts addition

Added a bypassing capacitor of 2.2μF/16V (TDK, C2012X7R1C225K125AB) next to the LC
Added a protection diode (Vishay, BAT43), Vf < 330 mV (Ta = 25 °C, If = 2 mA), Ir < 0.5 μA (Ta = 25 °C, Vr = 25 V)

LC resonant frequency of the LC resonator

L : Inductance [μH]

f₀ : Self resonant frequency [MHz]

f_m : L,Q measurement frequency (f_m) [MHz]

Q_m : Quality factor at f_m

R_s : Equivalent series resistance (at F_m) ≈ [Ω]

C_p : Parallel capacitance [pF]

f_r : Resonant frequency ≈ [MHz]
Q_e : Estimated quality factor (at F_r) ≈

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

C_bypass=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

Added a bypassing capacitor of 2.2μF/16V (TDK, C2012X7R1C225K125AB) next to the LC
Added a protection diode (Vishay, BAT43), Vf < 330 mV (Ta = 25 °C, If = 2 mA), Ir < 0.5 μA (Ta = 25 °C, Vr = 25 V)

Results (T_a=27°C, V_battery=4.7V, f_LC)

_battery

t_diagnostic= 27s → 8.5s
t_ustrip= 97s → 31s
t_nqueen=(79m10s) → 25m5s

Power supply current (Ta=27°C, V_battery=4.5V(SR44×3), f_LC=2.8MHz)

I_run≈2.5mA,
I_idle≈26μA,
I_standby<0.1μA

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

L_osc=180μH (R_s=5.5Ω) → 47μH (API Delevan, S1812R-473K), R_s= 3.5Ω, Shielded
C_osc=180pF → 68pF/C0G (Kemet, C0805C680J5GACTU), 50V, 2012M
C_bypass=22μF/10V/Ta → 100μF/6.3V (Murata, GRM31CR60J107ME39L), X5R, 3216M

Parts addition

Added a bypassing capacitor of 2.2μF/16V (TDK, C2012X7R1C225K125AB) next to the LC
Added a protection diode (Vishay, BAT43), Vf < 330 mV (Ta = 25 °C, If = 2 mA), Ir < 0.5 μA (Ta = 25 °C, Vr = 25 V)

Results (T_a=27°C, V_battery=4.76V, f_LC)

_battery

t_diagnostic= 27s → 8.5s
t_ustrip= 97s → 31s
t_nqueen=(79m10s) → 25m16s

Experimental modification for quad-speed 15C (#2614A06612)

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

Parts replacement

L_osc=180μH(R_s=5.5Ω) → 47μH(API Delevan S1812R-473K, Shielded, R_s=3.5Ω)
C_osc=180pF → 47pF (Taiyo-Yuden UMK212CH470J) | 33pF (Taiyo-Yuden UMK212CH330J) | 27pF (Taiyo-Yuden UMK212CH270J)
C_bypass=22μF/10V/Ta → 100μF/6.3V/MLCC (TDK C3225JB0J107M)

Parts addition

Added a bypassing capacitor next to the LC, 10μF/6.3V/MLCC (Murata, GRM21BB10J106KE01)
Added a bypassing capacitor next to the CPU, 10μF/35V/MLCC (Taiyo-Yuden GP075F106Z-A-B Axial lead)
Added a protection diode (Vishay, BAT43), Vf < 330 mV (Ta = 25 °C, If = 2 mA), Ir < 0.5 μA (Ta = 25 °C, Vr = 25 V)

The self-diagnostics-test ([ON]+[×]) results at various voltage and LC conbination, and N-queens benchmark results.

T_a=27°C Osillator inductor and capacitor Comment

47μH, 47pF 47μH, 33pF 47μH, 27pF

V_battery I_battery Result I_battery Result I_battery Result

4.7V 2.9mA O.K. 3.2mA O.K. 3.4mA O.K. Nominal voltage of SR44×3 at 20°C

3.8V 2.1mA O.K. 2.4mA O.K. 2.5mA O.K. Cut-off voltage of SR44×3 at -10°C

3.6V 2.0mA O.K. 2.2mA O.K. 2.5mA O.K. -

3.5V 1.9mA O.K. 2.1mA O.K. 2.2mA O.K. Low battery indicator turns on when
V_battery ≤ 3.5V

3.4V 1.9mA O.K. 2.0mA O.K. - FAIL

3.3V 1.8mA O.K. - FAIL - FAIL

3.2V 1.7mA O.K. - FAIL - FAIL

3.1V 1.6mA O.K. - FAIL - FAIL

3.0V - FAIL - FAIL - FAIL

2.7V
Cut-off voltage of LR44×3 at 20°C

t_N-queens 23m15s 20m30s 19m25s V_battery=4.7V, T_a=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.

REFERENCE

APPENDIX - Program library

Factr - Factor a positive integer
Frac - Fractional approximation
LCM/GCD - LCM and GCD of two positive integers
LCR - Resonant frequency of a LC resonator
μZw, μwZ - Synthesize/Analyze microstrip transmissionline
RI - Rational interpolation
Z→S - Impedance Z to S₁₁ scattering parameter conversion

L : Inductance	[μH]
f₀ : Self resonant frequency	[MHz]
f_m : L,Q measurement frequency (f_m)	[MHz]
Q_m : Quality factor at f_m
R_s : Equivalent series resistance (at F_m) ≈	[Ω]
C_p : Parallel capacitance	[pF]
f_r : Resonant frequency ≈	[MHz]
Q_e : Estimated quality factor (at F_r) ≈

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

T_a=27°C	Osillator inductor and capacitor						Comment
T_a=27°C	47μH, 47pF		47μH, 33pF		47μH, 27pF
V_battery	I_battery	Result	I_battery	Result	I_battery	Result
4.7V	2.9mA	O.K.	3.2mA	O.K.	3.4mA	O.K.	Nominal voltage of SR44×3 at 20°C
3.8V	2.1mA	O.K.	2.4mA	O.K.	2.5mA	O.K.	Cut-off voltage of SR44×3 at -10°C
3.6V	2.0mA	O.K.	2.2mA	O.K.	2.5mA	O.K.	-
3.5V	1.9mA	O.K.	2.1mA	O.K.	2.2mA	O.K.	Low battery indicator turns on when V_battery ≤ 3.5V
3.4V	1.9mA	O.K.	2.0mA	O.K.	-	FAIL
3.3V	1.8mA	O.K.	-	FAIL	-	FAIL
3.2V	1.7mA	O.K.	-	FAIL	-	FAIL
3.1V	1.6mA	O.K.	-	FAIL	-	FAIL
3.0V	-	FAIL	-	FAIL	-	FAIL
2.7V	-	FAIL	-	FAIL	-	FAIL	Cut-off voltage of LR44×3 at 20°C
t_N-queens	23m15s		20m30s		19m25s		V_battery=4.7V, T_a=27°C

Triple speed modification (#2614A06612)

Triple speed modification (#2813A62318)

Experimental modification for quad-speed 15C (#2614A06612)

Conclusion

SEE ALSO

REFERENCE

APPENDIX - Program library