obd: Allow starting OBD with low power enabled

alistair23 · alistair23 · commit d2c9291e65ba · 2019-03-01T17:55:49.000-08:00
Add support for connecting to an ELM device that is already in low power
mode.

Signed-off-by: Alistair Francis &lt;alistair@alistair23.me&gt;
diff --git a/docs/Connections.md b/docs/Connections.md
@@ -20,7 +20,7 @@ connection = obd.OBD(ports[0]) # connect to the first port in the list
 
 <br>
 
-### OBD(portstr=None, baudrate=None, protocol=None, fast=True, timeout=0.1, check_voltage=True):
+### OBD(portstr=None, baudrate=None, protocol=None, fast=True, timeout=0.1, check_voltage=True, start_low_power=False):
 
 `portstr`: The UNIX device file or Windows COM Port for your adapter. The default value (`None`) will auto select a port.
 
@@ -39,6 +39,8 @@ Disabling fast mode will guarantee that python-OBD outputs the unaltered command
 
 `check_voltage`: Optional argument that is `True` by default and when set to `False` disables the detection of the car supply voltage on OBDII port (which should be about 12V). This control assumes that, if the voltage is lower than 6V, the OBDII port is disconnected from the car. If the option is enabled, it adds the `OBDStatus.OBD_CONNECTED` status, which is set when enough voltage is returned (socket connected to the car) but the ignition is off (no communication with the vehicle). Setting the option to `False` should be needed when the adapter does not support the voltage pin or more generally when the hardware provides unreliable results, or if the pin reads the switched ignition voltage rather than the battery positive (this depends on the car).
 
+`start_low_power`: Optional argument that defaults to `False`. If set to `True` the initial connection will take longer (roughly 1 more second) but will support waking the ELM327 from low power mode before starting the connection. It does this by sending a space to the chip to trigger a charecter being received on the RS232 input line. This is sent before the baud rate is setup, to ensure the device is awake to detect the baud rate.
+
 <br>
 
 ---
diff --git a/obd/asynchronous.py b/obd/asynchronous.py
@@ -46,9 +46,10 @@ class Async(OBD):
     """
 
     def __init__(self, portstr=None, baudrate=None, protocol=None, fast=True,
-                 timeout=0.1, check_voltage=True, delay_cmds=0.25):
+                 timeout=0.1, check_voltage=True, start_low_power=False,
+                 delay_cmds=0.25):
         super(Async, self).__init__(portstr, baudrate, protocol, fast,
-                                    timeout, check_voltage)
+                                    timeout, check_voltage, start_low_power)
         self.__commands = {}   # key = OBDCommand, value = Response
         self.__callbacks = {}  # key = OBDCommand, value = list of Functions
         self.__thread = None
diff --git a/obd/elm327.py b/obd/elm327.py
@@ -104,7 +104,7 @@ class ELM327:
     _TRY_BAUDS = [38400, 9600, 230400, 115200, 57600, 19200]
 
     def __init__(self, portname, baudrate, protocol, timeout,
-                 check_voltage=True):
+                 check_voltage=True, start_low_power=False):
         """Initializes port by resetting device and gettings supported PIDs. """
 
         logger.info("Initializing ELM327: PORT=%s BAUD=%s PROTOCOL=%s" %
@@ -134,6 +134,11 @@ def __init__(self, portname, baudrate, protocol, timeout,
             self.__error(e)
             return
 
+        # If we start with the IC in the low power state we need to wake it up
+        if start_low_power:
+            self.__write(b" ")
+            time.sleep(1)
+
         # ------------------------ find the ELM's baud ------------------------
 
         if not self.set_baudrate(baudrate):
diff --git a/obd/obd.py b/obd/obd.py
@@ -50,7 +50,7 @@ class OBD(object):
     """
 
     def __init__(self, portstr=None, baudrate=None, protocol=None, fast=True,
-                 timeout=0.1, check_voltage=True):
+                 timeout=0.1, check_voltage=True, start_low_power=False):
         self.interface = None
         self.supported_commands = set(commands.base_commands())
         self.fast = fast  # global switch for disabling optimizations
@@ -61,11 +61,12 @@ def __init__(self, portstr=None, baudrate=None, protocol=None, fast=True,
 
         logger.info("======================= python-OBD (v%s) =======================" % __version__)
         self.__connect(portstr, baudrate, protocol,
-                       check_voltage)  # initialize by connecting and loading sensors
+                       check_voltage, start_low_power)  # initialize by connecting and loading sensors
         self.__load_commands()  # try to load the car's supported commands
         logger.info("===================================================================")
 
-    def __connect(self, portstr, baudrate, protocol, check_voltage):
+    def __connect(self, portstr, baudrate, protocol, check_voltage,
+                  start_low_power):
         """
             Attempts to instantiate an ELM327 connection object.
         """
@@ -82,14 +83,16 @@ def __connect(self, portstr, baudrate, protocol, check_voltage):
             for port in port_names:
                 logger.info("Attempting to use port: " + str(port))
                 self.interface = ELM327(port, baudrate, protocol,
-                                        self.timeout, check_voltage)
+                                        self.timeout, check_voltage,
+                                        start_low_power)
 
                 if self.interface.status() >= OBDStatus.ELM_CONNECTED:
                     break  # success! stop searching for serial
         else:
             logger.info("Explicit port defined")
             self.interface = ELM327(portstr, baudrate, protocol,
-                                    self.timeout, check_voltage)
+                                    self.timeout, check_voltage,
+                                    start_low_power)
 
         # if the connection failed, close it
         if self.interface.status() == OBDStatus.NOT_CONNECTED:
