Operation Manual

65 of 94ELM327DSJ Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
ELM327
to cause the ELM327 to shift to Low Power operation,
if there is no OBD activity for some time. If you follow
the logic path, you will see that b7 and b5 of PP 0F
must both be ‘1’, as well as b7 of PP 0E in order to
allow this switch to occur. The default time that it
allows before switching is set by b4, unless you have
set a value with the AT AMT command. Setting the
Activity Monitor Timeout to 00 blocks all the Activity
Monitor outputs.
The final way to enter the low power mode is by a
low level appearing at the ignition monitor input
(pin 15), with both b2 and b7 of PP 0E set to ‘1’.
The ignition monitor logic inserts a short internal
delay (‘debounce’) to be sure that the low level seen is
a legitimate ‘key off’ and not just some noise. After it is
sure, the ELM327 will then send a low power alert
message (‘LP ALERT’), and 2 seconds later it will
switch to Low Power operation, just the same as was
Figure 6. Enabling the Low Power Mode
Power Control (continued)
OBD
inputs
AT LP
command
b4
b7
b5
1 min
remaining
print
LP ALERT
b7
Go to
Low Power
65 msec
debounce
IgnMon
(pin 15)
voltage
is low
RS232 Rx
(pin 18)
input is
quiet
all are
quiet
sent a
message
not
monitoring
b0*
flash OBD
Tx LED
activity
monitor
timer ≥
setting?
AMT ≠ 00
b3*
print
ACT ALERT
b7
b5*
1 sec
delay
2 sec
delay
b3
print
ACT ALERT
1 sec
delay
RS232
detector
not
monitoring
b7
b2
voltage
monitor
Notes
PP 0F bits are shown with an asterisk (*).
All other bits are for PP 0E.
represents an AND gate
represents an OR gate
5 min or 20 min
timer
(read with
AT AMC)
timer
Timeout setting
AMT value, if set
else
150 sec if b4*= 1
30 sec if b4*= 0
yes
b7*