ELM329
Compatibility with the ELM327
In designing the ELM329, we have purposely
maintained an almost identical pinout with our ELM327
integrated circuit. What this means is that you can
remove the ELM327 chip from its circuit and simply
insert an ELM329 chip, without causing damage to the
ELM329.
There is only one consideration that we are aware
of if you do this - the 510W resistors that are used for
the ‘K’ and ‘L’ lines may get hot. If you are going to use
an ELM327 circuit with our ELM329, we recommend
that you either:
excessive heat, or causing other problems.
Another consideration is software. The ELM329
uses many of the same instructions as the ELM327,
and even pretends to support protocols 1 to 5 in order
to be more compatible with it, so the software needed
will be almost identical. The one problem that you may
encounter would be with software that is set to only
work with certain chips (ie. if it looks for ELM320,
ELM322, ELM323, or ELM327 ID strings). If that is the
case, it would not be too big a task for the software
developers to add this new chip to their list - that may
very well be done even before you read this.
- disconnect the 510Wresistors (you may be able
to simply lift one end), or
- replace the 510Wresistors with a higher value
resistance (2K or greater), or
- set PP 20 to 00
Any of the above will allow the ELM329 to function
in an existing ELM327 circuit without generating
Modifications for Low Power Standby Operation
The ELM329 may be placed in a low power
standby mode in which it consumes very little current.
This will find its greatest use with semi-permanent
vehicle installations where you want the current
consumption to be as low as possible (ideally zero)
when the ELM329 is not needed.
Just how effective the low power mode is depends
on your attention to detail when designing your circuit.
If you use our example circuit of Figure 9, you will
likely find that with 12.0V applied as ‘Battery Positive’,
the measured current is typically:
The “Low Power Mode” of operation section (page
57) discussed the ways in which you might initiate low
power operation, but the easiest is to use the low
power command (AT LP). After sending this, the total
circuit current is then typically:
current after AT LP = 0.5 mA
This is a very low current, and may be suitable for
your application as it is. In fact, it is a reduction of 99%
from the typical operating current. Note that whether
the Active LED is set to flash or not has very little
influence on this current (it uses an average of about
25 µA). Similarly, the CAN Monitor typically only uses
about 20 µA during low power operation, so does not
appreciably affect the total current. The largest current
is typically from the CAN transceiver. If you choose a
low current one (eg. the infineon TLE7250) then total
circuit current can likely be reduced to under 0.2 mA.
It is difficult to reduce the standby current further
than that, but you may be able to do so by carefully
selecting components. You might consider eliminating
the voltage monitoring circuit (R9 and R10), and you
could review our choice of voltage regulators for
example. We leave those improvements to you.
base current (on the bench) = 24.8 mA
when simply powered on the bench, with no PC or
ECU connected. If you connect it to a vehicle and a
computer, the current typically rises to:
base current (in the vehicle) = 32.3 mA
with the Active LED on. When actually monitoring
data, this current rises, and has been measured at:
active current (in the vehicle) = 45.8 mA
Any power supply designs should be able to
supply this last current continuously, and be able to
supply more than that under transient conditions.
ELM329DSB
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
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