This device is a microcontroller which is designed to interface a personal computer or laptop with a vehicle's On Board Diagnostic (OBD II) interface. It is intended to function with all protocols used by vehicle manufacturers to implement the OBD II system as defined by SAE and ISO specifications. The OBD II system became mandatory for 1996 and up vehicles, but some vehicles were already fully or partially compatible with OBD II requirements prior to 1996. The chip is not suitable for the earlier vehicles such as OBD I. The device is intended to function as a simple scan tool and is capable of sending and receiving any OBD II message defined in SAE J1979 for any of the three types of OBDII bus implementations (PWM, VPW, ISO 9141-2). It can also be used as an inexpensive interface for custom instrumentation monitoring various vehicle parameters such as speed, RPM, coolant or intake air temperature, engine load, intake air flow rate, etc.
Components:
D1=1N4001
D2,S3,D4,D5=1N4148
L1,L2,L3,L4=Yellow LED
L5=Green LED
Q1,Q3,Q5,Q6,Q7,Q9=2N3904(NPN)
Q2,Q4,Q8=2N3906(PNP)
U1=ELM327
U2=MCP2551
U3=78L05(5V, 100mA regulator)
U4=317L (adj. 100 mA regulator)
C1,C2,C5,C6,C7=0.1uF 16V
C3,C4=27p
C8,C9=560pF
R32,R33=100 Ohm
R5=240 Ohm
R1,R2,R3,R4,R27,R28,R29,R30=470 Ohm
R17,R19=510 Ohm 1/2W
R16,R18=2.2 KOhm
R6,R7,R14,R15,R23,R26,R31=4.7 KOhm
R8,R9,R11,R13,R22,R24,R25,R35=10 KOhm
R10,R21,R36=22 KOhm
R20,R34=47 KOhm
R12=100 KOhm
X1=4.000MHz crystal
RS232 conn=DB-9 female
IC Socket=28 pin 0.3 (or 2x14 pin)
correct
incorrect