ELM327P datasheet(68/76 Pages) ELM

68 / 76 page

Resistors (1/8W or greater, except as noted)

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 (adjustable 100mA regulator)

Capacitors (16V or greater, except as noted)

C1, C5 = 0.1uF 50V

C2, C6, C7 = 0.1uF

C3, C4 = 27pF

C8, C9 = 560pF 50V

Figure 10. Parts List for Figure 9

Example Applications (continued)

68 of 76

ELM327DSH

Elm Electronics – Circuits for the Hobbyist

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ELM327

been eliminated. The voltage switching circuitry has

been reduced to a single 8V regulator as well, since

there will be no need to switch to 5V. Note that pin 3

has been intentionally left open-circuited as it is not

required by the voltage regulator.

The first time that this circuit is used, it will likely be

set to protocol 0, the default ‘automatic search’ mode

of operation (as shipped from the factory). When you

connect it to the J1850 VPW vehicle, it will then

automatically detect the protocol, and if the memory is

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

new default, with no action 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 will be 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, the ELM327 will remain

set for protocol 2, whether it fails to make a connection

or not.

Depending on the circumstances, you may be able

to simplify this circuit even further, by possibly using

the USB connection to obtain 5V for the ELM327,

rather than the 78L05 regulator shown. We caution

that some protocols (CAN for example), may draw

more current than your USB connection is able to

supply, so review this first.

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. The following section shows how you

might be able to optimize these circuits to reduce

power consumption…

ELM327P Datasheet(PDF) 68 Page - ELM Electronics

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