ELM327P datasheet(49/51 Pages) ELM

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ELM327

ELM327DSC

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Resistors

R32, R33= 100

Ω

R5 = 240

Ω

R1, R2, R3, R4, R27, R28, R29, R30 = 470

Ω

R17, R19 = 510

Ω 1/2W

R16, R18 = 2.2 K

Ω

R6, R7, R14, R15, R23, R26, R31 = 4.7 K

Ω

R8, R9, R11, R13, R22, R24, R25, R35 = 10 K

Ω

R10, R21, R36 = 22 K

Ω

R20, R34 = 47 K

Ω

R12 = 100 K

Ω

Misc

X1 = 4.000MHz crystal

RS232 Conn = DB9F

IC Socket = 28pin 0.3” (or 2 x 14pin)

Semiconductors

D1 = 1N4001

D2, D3, 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. 100mA regulator)

Capacitors

C1, C2, C5, C6, C7 = 0.1uF 16V

C3, C4 = 27pF

C8, C9 = 560pF

Figure 10. Parts List for Figure 9

Example Applications (Cont’d)

proceed to try J1850 VPW. If the memory is enabled

(as shown), J1850 VPW will then become the new

default, with no input required by you. This will work

well for most applications, but if the circuit is used on a

vehicle with the key off, for example, then it will again

go searching for a new protocol. In general, you do not

want this to happen every time. It may be only a minor

inconvenience to have to wait while the ELM327

determines that it is “UNABLE TO CONNECT”, but

why go through it if you do not have to? If you know

that you are using the circuit in a J1850 VPW only

application (protocol 2) then you should issue the

command AT SP 2 the very first time that the circuit is

powered. From that point on, it will remain in protocol

2, whether it fails to make a connection or not.

This has provided two examples of how the

ELM327 integrated circuit might be used. Hopefully it

has been enough to get you started on your way to

many more… we hope that you enjoy the journey!

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