ELM327LP datasheet(82/94 Pages) ELM

82 / 94 page

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

R22, R23 = 100

Ω

R3, R5, R27, R28, R29, R30, R31 = 470

Ω

R17, R19 = 510

Ω 1/2W

R2, R4, R16, R18 = 2.2 K

Ω

R1, R7, R14, R15, R24, R32 = 4.7 K

Ω

R6, R9, R11, R13, R26 = 10 K

Ω

R10, R8 = 22 K

Ω

R21 = 33K

Ω

R12, R20, R25 = 47 K

Ω

Capacitors (16V or greater, except as noted)

C3, C4 = 27pF

C7, C8 = 560pF 50V

C1 = 0.1uF 50V

C2, C5, C6 = 0.1uF

C9 = 10uF

Semiconductors

D1 = 1N4001

D2, D3, D4 = 1N4148

L1, L2, L3, L4 = Yellow LED

L5 = Green LED

Q1, Q3, Q5, Q6, Q7 = 2N3904 (NPN)

Q2, Q4 = 2N3906 (PNP)

U1 = ELM327L

U2 = MCP2551 or MCP2561

U3 = 7805 regulator (5V 1A)

U4 = 317L adjustable regulator (100 mA)

U5 = FTDI DBP-USB-D5-F usb module

Misc

X1 = 4.000MHz crystal

DB9M connector for OBD cable?

IC Socket = 28 pin 0.3" wide (or 2 x 14pin)

Figure 10. Parts List for Figure 9

Example Applications (continued)

you will need to add a jumper or two on the unused

inputs. See the ‘Unused Pins’ section for advice on

what to connect the pins to.

Some people still prefer to interface their circuits

with standard RS232 circuitry. For these, we offer the

sub-circuits of Figures 11 and 12.

Figure 11 shows a discrete RS232 interface, that

may be connected directly to the ELM327. This circuit

uses a resistor, diode, and capacitor between the two

RS232 signal lines to ‘steal’ power from the host

computer. In this way, the required RS232 negative

voltage is obtained without adding a complicated

power supply to the ELM327 circuit. The RS232

connections shown are for a standard 9 pin connector.

If you are using a 25 pin one, you will need to

compensate for the differences. This circuit works well

at baud rates of 57600 bps or less, but begins to show

some errors at rates of 115200 bps and above.

The circuit of Figure 12 offers another RS232

solution that works well at higher baud rates. It uses a

Maxim product (the MAX3222E) that is capable of

operating at up to a 250 kbps rate (be sure to visit

www.maximintegrated.com for more information).

The

MAX3222E

RS232

transceiver

contains

ELM327L

82 of 94

ELM327L DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Figure 11. A Low Speed

RS232 Interface (

≤ 57.6 kbps)

2 (RxD)

RS232

Interface

(DB9F)

+5V

3 (TxD)

5 (SG)

1 (DCD)

4 (DTR)

6 (DSR)

7 (RTS)

8 (CTS)

4.7K

Ω

10K

Ω

10K

Ω

0.1µF

4.7K

Ω

10K

Ω

+5V

327

2N3904

2N3906

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