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.
66 lines
1.7 KiB
Plaintext
66 lines
1.7 KiB
Plaintext
* BMW I/K-Bus Interface - RX Path (Bus to ESP32) - PC817 Optocoupler
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* Bus drives byte 0x50 (MFL addr) at 9600 baud 8E1
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* 0x50 = 01010000, LSB first = 00001010, even parity = 0
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* Frame: START(0) d0(0) d1(0) d2(0) d3(0) d4(1) d5(0) d6(1) d7(0) P(0) STOP(1)
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* Bus: 12V=idle/HIGH, 0V=active/LOW, bit time=104.17us
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* ESP32 GPIO thresholds: LOW < 0.825V, HIGH > 2.475V
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*
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* PC817 pin order: 1=Anode, 2=Cathode, 3=Collector, 4=Emitter
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* U1 config: emitter-follower (collector to VCC, emitter to RX output)
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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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* === Bus Model ===
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* External module driving byte 0x50 through 100R source impedance
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V_BUS V_BUS_SRC 0 PWL(
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+ 0u 12
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+ 199.5u 12
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+ 200u 0
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+ 720.33u 0
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+ 720.83u 12
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+ 824.5u 12
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+ 825u 0
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+ 928.67u 0
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+ 929.17u 12
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+ 1032.83u 12
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+ 1033.33u 0
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+ 1241.17u 0
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+ 1241.67u 12
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+ 2000u 12)
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R_BUS V_BUS_SRC IBUS 100
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C_BUS IBUS 0 100p
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* === RX Optocoupler (U1) ===
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* Bus HIGH (12V): LED on -> phototransistor ON -> RX HIGH
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* Bus LOW (0V): LED off -> phototransistor OFF -> RX LOW (via R4)
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R1 IBUS U1_A 2k
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XU1 U1_A 0 VCC RX PC817 Igain=1m
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R4 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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* === Simulation ===
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.tran 0 2000u 0 0.1u
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* === Measurements ===
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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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.meas tran IBUS_HIGH MAX V(IBUS)
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.meas tran IBUS_LOW MIN V(IBUS)
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.meas tran LED_CURRENT_MAX MAX I(R1)
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.meas tran RX_RISE TRIG V(RX) VAL=0.825 RISE=1 TARG V(RX) VAL=2.475 RISE=1
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.meas tran RX_FALL TRIG V(RX) VAL=2.475 FALL=1 TARG V(RX) VAL=0.825 FALL=1
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.backanno
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.end
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