Ryan Malloy
30ef51f26c
Both signal paths validated with LTspice using built-in PC817 subcircuit model (Igain=1m). RX gives clean 0-3.13V at 3.3V VCC with 5.8us rise time. TX confirms signal inversion and 0.17V bus LOW with 4.66mA LED drive. 3.3V design works but is marginal vs the original 5V Arduino circuit at worst-case CTR.
81 lines
2.5 KiB
Plaintext
81 lines
2.5 KiB
Plaintext
* BMW I/K-Bus Interface - TX Path (ESP32 to Bus) - PC817 + BC547
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* MCU TX drives Q1 (BC547B) which drives U2 (PC817) LED
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* U2 phototransistor pulls bus LOW against 4.7k pull-up to 12V
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* Test pattern: alternating 3-bit-time (312us) pulses
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* TX 0V = bus idle (HIGH), TX 3.3V = bus active (LOW via U2)
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* Includes U1 RX path for loopback observation
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* Signal inversion: TX HIGH -> bus LOW (documented in design)
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*
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* PC817 pin order: 1=Anode, 2=Cathode, 3=Collector, 4=Emitter
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* === Power Supplies ===
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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 ===
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* 0V=idle (U2 OFF, bus HIGH), 3.3V=active (U2 ON, bus LOW)
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* Alternating ~3 bit times (312us) to show inversion
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V_TX TX 0 PWL(
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+ 0u 0
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+ 199.5u 0
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+ 200u 3.3
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+ 512u 3.3
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+ 512.5u 0
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+ 825u 0
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+ 825.5u 3.3
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+ 1137u 3.3
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+ 1137.5u 0
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+ 2000u 0)
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* === Bus Model ===
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* Idle pull-up: represents combined impedance of other modules' inputs
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* No active driver — only U2 phototransistor drives the bus here
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R_PULL V12 IBUS 4.7k
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C_BUS IBUS 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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* LED path: VCC -> R2 -> U2 anode(1) -> U2 cathode(2) -> Q1 collector
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* Phototransistor: collector(3) = IBUS, emitter(4) = GND
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R2 VCC U2_A 470
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XU2 U2_A Q1C IBUS 0 PC817 Igain=1m
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* === RX Optocoupler (U1) for Loopback ===
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* Shows what the MCU sees on RX when it transmits
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R1_RX IBUS 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 (inlined from LTspice library) ===
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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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* === Transistor 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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* === Simulation ===
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.tran 0 2000u 0 0.1u
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* === Measurements ===
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.meas tran IBUS_HIGH MAX V(IBUS)
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.meas tran IBUS_LOW MIN V(IBUS)
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.meas tran IBUS_SWING PP V(IBUS)
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.meas tran TX_TO_BUS_DELAY TRIG V(TX) VAL=1.65 RISE=1 TARG V(IBUS) VAL=6 FALL=1
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.meas tran U2_LED_CURRENT MAX I(R2)
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.meas tran RX_LOOPBACK_HIGH MAX V(RX)
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.meas tran RX_LOOPBACK_LOW MIN V(RX)
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.meas tran Q1_BASE_CURRENT MAX I(R3)
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.backanno
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.end
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