ELM327
Example Applications (continued)
+5V
Q9
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 13 offers another solution that
works well at higher baud rates. It uses a Maxim
product (the MAX3222E) that is capable of 250 kbps
operation. Visit www.maximintegrated.com for more
information.
The MAX3222E RS232 transceiver contains
internal charge pump circuitry that generates the
voltages required for RS232 communications, in
addition to the analog interface circuitry needed. All
you have to do is provide a few capacitors, and it does
the rest.
We do caution that the MAX3222E does seem to
place some extra demands on the 5V power supply,
so if you use it, we recommend changing some
capacitors in the circuit of Figure 9. We suggest
changing C5 from 2.2 µF to 10 µF, and C7 from 10 µF
to 33 µF (their voltage ratings stay the same). If after
these changes, you still see the occasional ‘LV
RESET’, you may wish to consider a more powerful
regulator.
RS232
Interface
(DB9F)
R26
4.7KW
R24
10KW
3 (TxD)
R25
10KW
D5
D4
C5
5 (SG)
+5V
Q8
0.1µF
R22
10KW
R23
4.7KW
2 (RxD)
+5V
1 (DCD)
4 (DTR)
6 (DSR)
19
18
17
16
15
327
7 (RTS)
8 (CTS)
Figure 12.
A discrete RS232 Interface
Many wireless modules (WiFi or Bluetooth®) use
serial interfaces just like what we have shown for the
RS232 connections. Connecting to them should not be
very difficult if you follow the manufacturers directions.
If you are considering Bluetooth, you might read our
‘AN-04 ELM327 and Bluetooth®’ application note first.
This has provided a few examples of how the
ELM327 integrated circuit might typically 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…
RS232
Interface
(DB9F)
3 (TxD)
2 (RxD)
5 (SG)
10
11
12
13
14
9
8
7
6
5
4
3
2
1
1 (DCD)
4 (DTR)
15
16
+5V
0.1µF
17
18
6 (DSR)
7 (RTS)
8 (CTS)
0.1µF
+5V
19
18
17
16
15
Figure 13.
An Integrated RS232 Interface
327
ELM327DSI
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