Ryan Malloy
e6fc5ad4e9
R2 sweep (47-470 ohm) and CTR grade sweep at ISO 9141 minimum bus impedance. R2<=100 ohm works; BMW's R2=220 does not. Confirms transistor design is better fit for OBD-II K-line.
71 lines
1.9 KiB
Plaintext
71 lines
1.9 KiB
Plaintext
* Optocoupler (PC817) vs K-Line: Can it handle 510 ohm pull-up?
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* Tests BMW opto design against OBD-II K-line worst-case impedance
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* R2 sweep to find if any value works at 510 ohm + 10400 baud
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* PC817 pin order: 1=Anode, 2=Cathode, 3=Collector, 4=Emitter
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.param R2val 220
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V_BAT V12 0 12
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V_MCU VCC 0 3.3
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* === TX Test Signal at 10400 baud (96.15us bit period) ===
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* Two pulses to show both edges
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V_TX TX 0 PWL(
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+ 0u 0
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+ 99u 0
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+ 100u 3.3
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+ 292u 3.3
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+ 292.5u 0
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+ 580u 0
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+ 580.5u 3.3
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+ 772u 3.3
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+ 772.5u 0
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+ 1500u 0)
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* === K-Line Bus Model: 510 ohm pull-up (ISO 9141 minimum spec) ===
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R_PULL V12 KLINE 510
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C_BUS KLINE 0 100p
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* === TX Driver: Q1 (BC547B) ===
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R5 TX R5_R3 470
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R3 R5_R3 Q1B 10k
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Q1 Q1C Q1B 0 BC547B
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* === TX Optocoupler (U2) ===
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R2 VCC U2_A {R2val}
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XU2 U2_A Q1C KLINE 0 PC817 Igain=1m
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* === RX Optocoupler (U1) on same K-Line wire ===
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R1_RX KLINE U1_A 2k
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XU1 U1_A 0 VCC RX PC817 Igain=1m
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R4_RX RX 0 1k
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* === PC817 Subcircuit ===
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.subckt PC817 1 2 3 4
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R1 N003 2 2
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D1 1 N003 LD
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G1 3 N004 N003 2 {Igain}
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C1 1 2 18p
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Q1 3 N004 4 [4] NP
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.model LD D(Is=1e-20 Cjo=18p)
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.model NP NPN(Bf=1200 Vaf=140 Ikf=100m Rc=1 Cjc=19p Cje=7p Cjs=7p C2=3e-15)
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.ends PC817
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* === BC547B Model ===
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.model BC547B NPN(IS=2.39E-14 NF=1.008 ISE=3.545E-15 NE=1.541 BF=294.3 IKF=0.1357 VAF=63.2 NR=1.004 ISC=6.272E-14 NC=1.243 BR=7.946 IKR=0.1144 VAR=25.9 RB=1 IRB=1.00E-06 RBM=1 RE=0.4683 RC=0.85 XTB=0 EG=1.11 XTI=3 CJE=1.358E-11 VJE=0.65 MJE=0.3279 TF=4.391E-10 XTF=120 VTF=2.643 ITF=0.7495 PTF=0 CJC=3.728E-12 VJC=0.3997 MJC=0.2955 XCJC=0.6193 TR=1.00E-32 CJS=0 VJS=0.75 MJS=0.333 FC=0.9579 Vceo=45 Icrating=100m mfg=NXP)
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* === Sweep R2 to find what works at 510 ohm bus ===
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.step param R2val list 47 68 100 150 220 330 470
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.tran 0 1500u 0 0.1u
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* === Measurements ===
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.meas tran KLINE_HIGH MAX V(KLINE)
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.meas tran KLINE_LOW MIN V(KLINE)
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.meas tran KLINE_SWING PP V(KLINE)
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.meas tran LED_CURRENT MAX I(R2)
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.meas tran RX_HIGH MAX V(RX)
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.meas tran RX_LOW MIN V(RX)
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.backanno
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.end
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