ELM327
Example Applications (continued)
+5V
+12V
USB
16
78L05
5.0V
TVS
Interface
(type ‘B’
connector)
Battery
Positive
+5V
PWR
470W
0.1µF
0.1µF
+5V
5
7
6
8
5
4
3
1 (+5)
2 (D-)
3 (D+)
4 (SG)
Signal
Ground
SiLabs
CP2102
1µF
26 25
0.1µF
+5V
+5V
+5V
4 x
470W
28
27
26
25
24
23
22
21
20
19
10
18
11
17
12
16
13
15
OBD
Interface
(J1962)
327
+5V
1
2
3
4
5
6
7
8
9
14
4.00MHz
27pF
+12V
78L08
27pF
10KW
4.7KW
Figure 11.
A J1850 VPW to USB Interpreter
4.7KW
22KW
10KW
2
J1850 Bus +
the value of PP 0C (the baud rate divisor), then
change your software to that same value. Changes to
PP 0C require a power down then power up in order
for them to take effect, so don’t forget that. Changing
PP 0C requires two steps. For example, to switch to
115200 baud, use these AT PP commands:
default to 115200 bps, rather than to 38400 bps. If you
go through the calculations, you will note that this baud
rate is actually off by about 0.8%, which should pose
no problems with modern interfaces.
Some people still prefer to interface their circuits
with standard RS232 circuitry. For these, we offer the
sub-circuits of Figures 12 and 13.
Figure 12 shows a discrete RS232 interface, that
may be connected directly to the ELM327. This circuit
uses a resistor, diode, and capacitor between the two
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
>AT PP 0C SV 23
OK
> AT PP 0C ON
OK
If you power down then up, the circuit will then
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