rpi_obd2

Minimalistic access to OBD2 data with an ELM327 compatible adapter

Connecting to Bluetooth-OBD on my openSUSE laptop

• Check whether the built-in bluetooth adapter is active or blocked
  • hciconfig -a or hciconfig dev
  • sudo rfkill list
• If it's blocked and/or down: unblock and activate it (order seems to be unimportant)
  • sudo rfkill unblock bluetooth
  • sudo hciconfig hci0 up
• Search for the bluetooth dongle
  • hcitool scan
  • This command reports the MAC address of all found BT devices, like 00:0B:0D:84:B3:A0
  • Check offered services with sdptool browse 00:0B:0D:84:B3:A0
• Bind the bluetooth donge to a rfcomm device
  • sudo rfcomm bind 0 00:0B:0D:84:B3:A0
  • Now the device /dev/rfcomm0 is created
• Try to connect to the device
  • cat /dev/rfcomm0
  • minicom -D /dev/rfcomm0
  • (call as sudo if you are not member of group dialout)
• TODO: CHECK what's the purpose of
  • rfcomm connect 0
  • l2ping -c3 00:0B:0D:84:B3:A0
• TODO: CHECK how to enter the PIN when there is no GUI (KDE asked me for the PIN ...)
  • ?? ==> http://www.linurs.org/linux/Bluetooth.html
  • ?? ==> https://en.wikibooks.org/wiki/Linux_Guide/Linux_and_Bluetooth
  • !!?? ==> https://www.raspberrypi.org/forums/viewtopic.php?f=53&t=53299 ==> https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=87138&p=752712#p752712
  • !!!! bluez-simple-agent ==> http://fabcirablog.weebly.com/blog/reading-a-cars-obdii-port-with-a-raspberry-pi || http://gersic.com/connecting-your-raspberry-pi-to-a-bluetooth-obd-ii-adapter/ || https://mobileandpi.wordpress.com/tag/bluez-simple-agent/ || http://bobbylindsey.com/blog/?p=14 || http://diyapps.blogspot.de/2015/02/eclipse-open-iot-challenge-obd-part1.html + http://diyapps.blogspot.de/2015/02/eclipse-open-iot-challenge-obd-part2.html

Useful ELM327 commands

Note: all commands must be terminated by \r (CR). Sending just a CR repeats the last command?!

AT commands

• ATZ Reset (ATD seems to be a synonym)
  • Most (all?) OBD2 dongles will send a version string as response
• ATDP Display used protocol (e.g. CAN)
  • Bus connection must be initialized first, e.g. by sending 0100
• ATE0 Disable character echo (default: ATE1: character echo on)
• ATL0 Disable sending LF after CR (default: ATL1: LF is sent after CR)
• ATS0 Disable sending spaces between hex characters (default: ATS1: spaces are sent between hex characters)
  • This command is not supported by my OBD2 dongle (apparently only a cheap ELM327 clone)

OBD2 data access: The first command sent after power up will initialize the bus connection and may take longer. The general command format is where

• SID is the Service ID (in our case always 01) and
• PID is the Parameter ID (identifying the parameter to read out)

All commands and responses are coded as 2-digit hex numbers without prefix. The response format is <SID | 0x04>

The following commands may be useful (see also https://en.wikipedia.org/wiki/OBD-II_PIDs)

• 0100 List supported PIDs in range 01..1F
  • returns 4 bytes as bitmask
• 0104 Engine load
  • returns 1 byte (A): LOAD_PCT[%] = A*100/255
• 010C Engine RPM
  • returns 2 bytes (A,B): RPM [1/min] = ((A*256)+B)/4
• 010D Vehicle Speed
  • returns 1 byte (A): VSS [km/h] = A
• 0110 Mass Air Flow
  • returns 2 bytes (A,B): MAF [g/s] = ((A*256)+B) / 100
  • not availble on my car
• 011F Run time since engine start
  • returns 2 bytes (A,B): RUNTIM [s] = (A*256)+B
• 0146 Ambient air temperature
  • returns 1 byte (A): AAT[°C] = A-40

References

• rfkill
• rfkill- ubuntuusers
• SDB:ELM327_based_ODB2_scan_tool

?? https://www.modmypi.com/blog/installing-the-raspberry-pi-nano-bluetooth-dongle ?? http://unix.stackexchange.com/questions/92255/how-do-i-connect-and-send-data-to-a-bluetooth-serial-port-on-linux ?? http://stackoverflow.com/questions/15028953/sending-binary-data-over-bluetooth-rfcomm-spp-converts-0x0a-to-0x0d-0x0a