OBD Chip Schematic

| Car/Engine 2008. 11. 14. 11:41

Posted by cloudmir

OBD-2 universal cable scheme forPWM,VPW, andISO 9141-2 vehicles pinout

This device is a CMOS 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 three of the 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.

OBD 2 universal cable

Components:

C5, C6  .01 UF, 25V
C4      .1 UF, 25V 
C3      .47 UF, 50V 
C2,C1    20 pf, 50V 
R11, R12, R23, R9, R1, R3, R4, R25, R8  10 KOhm, 1/4 Watt 
R24 18 KOhm, 1/4 W 
R19, R18, R7, R20, R22, R5, R6, R13 1 KOhm, 1/4 W 
R21 5.6 KOhm, 1/4 W
R16, R17 510 Ohm, 1/4 W
R10 62 KOhm, 1/4 W
R15 9.1 KOhm, 1/4 W
R14 270 Ohm, 1/2 W
R2   - Not used  
D2  1N4739 Zener, 9.1V, 1W 
D1, D3  1N4148 Diode
Q3, Q4, Q5 PN2222 Transistor, NPN
Q2 PN3904 Transistor, NPN
Q1 PN3906 Transistor, PNP
IC2 7805 Regulator, 5V
IC3 LM339N Quad Comparator 
IC1 16F84-20 Microprocessor (firmware 1.07)
XTL 1 20 MHz Crystal, 20 Mhz

If you don"t use PWM, you can omit R4, R6, R7, R8, R9, R10, Q1, Q2, D1.
If you don"t use ISO, you can omit R15, R16, R17, R18, R19, R21, Q4, Q5
If you don"t use VPW, you can omit R13, R14, R23, R24, D2, D3, Q3

Don"t connect external power sources - all power direved from pin 16 of OBDII

Serial port works at 19200 baud

Scheme is unuseful without .hex for IC1 firmware 1.07...

Can be replaced using scheme with ELM327 chip (http://www.elmelectronics.com/DSheets/ELM327DS.pdf). ELM327 even prvides more protocols, including CAN.

And

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OBD-2 universal cable scheme forPWM,VPW, andISO 9141-2 vehicles pinout

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