ELM329LP datasheet(79/87 Pages) ELM

79 / 87 page

Example Applications (continued)

ELM329L

79 of 87

ELM329L DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

>AT PP 0C SV 23

> AT PP 0C ON

That is all that is needed to reconfigure the

ELM329 for 115.2 kbps operation. This change stays

in effect through power downs and resets, but you can

change it again if you wish.

If you now reset the ELM329 (send AT Z or power

down then up), the ELM329 will begin operating at the

new rate of 115200 bps, rather than 38400 bps.

Change your software setting to also be 115200 bps,

and you should be communicating. If you go through

the calculations, you will note that the ELM329 baud

rate is actually off by about 0.8%, but modern UARTs

can typically handle rate errors of a few % without any

problems, so this is not an issue.

When working with the CP2102, we do caution

that it is very small and difficult to solder by hand, so

be prepared for that. Also, if you provide protection on

the data lines with transient voltage suppressors

(TVS’s), be careful when choosing devices, as some

exhibit a very large capacitance and will affect the

transmission of the USB data.

Our next circuit (Figure 14) shows one way to

interface a 5V ELM329 to circuits that operate at a

different voltage level. We show 3.3V as an example,

but it can actually be anything from 2.7V to 5.5V.

The circuit uses the ADuM1201 iCoupler chip from

Analog Devices (www.analog.com). In addition to

acting as a level translator, this device also provides

isolation (galvanic, to 2500 Vrms) between the two

sides. This is often desired in order to keep the vehicle

circuit completely separate from the computer circuit.

Typically, one might use a standard level shifter IC

to interface to 3.3V – for example the TXB0102 by

Texas Instruments (www.ti.com), or the ST2129 from

ST Microelectronics (www.st.com), but the ADuM1201

offers several other advantages. The main difference

is that it offers isolation, as mentioned, but it also can

be used with 2.7V to 5.5V on either side, it provides a

high output if the input side is unpowered, and it

typically uses less current and is much faster than

many opto-isolator solutions (the ‘1201 is capable of

data rates of 1 MHz or more). Of course there are a

couple disadvantages too. It does use current (almost

1 mA), so may be an issue if trying to reduce sleep

current to a minimum, and it does cost more than

devices like the TXB0102.

Many wireless modules (WiFi or Bluetooth®) use

serial interfaces just like what we have shown here for

the RS232 connections. Connecting to them should

not be very difficult if you follow the manufacturers

directions (and perhaps consider using devices like the

ADuM1201 or the TXB0102) if the supply voltages

differ. If you are considering using a Bluetooth

interface, you might read our ‘AN-04 ELM327 and

Bluetooth®’ application note first.

This has provided a few examples of how the

ELM329 integrated circuit might typically be used.

Hopefully it has been enough to get you started on

your way to many more. The next section shows how

you might be able to optimize these circuits to reduce

power consumption…

Figure 14. Connecting to a 3.3V System

+5V

n.c.

+5V

ADuM1201

Busy RTS

329

+5V

+3.3V

3.3V common

3.3V

Interface

ELM329LP датащи(PDF) 79 Page - ELM Electronics

ELM329LP датащи(HTML) 79 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

датащи скачать

ссылки URL