MP3Car.com - View Single Post - New Project: Linux ODB-II SBC

Synx · 09-06-2003, 07:50 PM

I have made such a device, its powered by a AM186ED microcontroller, using a full demo board so its got two built in serial ports, some flashrom for saving the embedde software on it etc. Anyways i did the entire project my self using this board and a 320x200 pixel SED1330 controlled monocrome graphics display. It currently only works with the ISO9141-2 hardware standard(almost all JAP spec cars, ie Nissan, Subaru, Toyota, etc). The ISO standard is really easy to design the hardware for because its basicly a serial link with slightly modified logic leves. Instead of the -6to-30V for a logic 1 on RS232A its +12V, and instead of +6to+30V for a logic 0 on RS232A its 0V. This is easy to convert and because you really need to optically isolate the connection anyways you can use the optoisolators to do the level shift and inversion for you. I would recomend purchaseing the ISO 9141-2 document if you are really serious. You are also gona need to learn the iirc. SAE J1978 OBDII protocal to use for communication. Basicly the SAE protocal is used ontop of the given hardware levels, ie ISO 9141-2, PWM, or VPW. Also in the very near future there will be a new standard called CAN. I would also recoment you purchase the SAE J1978 document. Both can be downloaded in PDF format for around $40 us iirc. Again this is only for ISO specific cars, so this will not work in Fords etc. I have not designed the hardware for the two other standards so im not sure how it could be done. BTW may i suggest the MAX232A chip to do your line level conversion *hint hint* if your just gona use the PC serial hardware.
Okay that was long and prob very confusing, sorry i have a hard time organiseing my thoughts on matters such as these. Anyways i wouldn't mind helping much as i am going to be porting my software to win32 soon i think so i can so a very similar thing for my Subaru WRX, its going to be a 2x16 CHAR lcd to display things such as Engine Load, EGT Temps, Coolent Temps, Boost levels(not sure if this is possible yet), etc. Good luck and i hope what i wrote was understandable.

EDIT:
Side note, if you going to be using a PIC controller or BAISC stamp type microcontroller, you had better have a dedicated CHIP to do the house keeping on the OBDII connection. You will have a VERY hard time trying to get the BAISC or PIC controller to keep on top of the strict timing requirements for OBDII. If you do decided to go this route there are IC's such as a few made by ELM that will do all the raw OBDII communication stuff for you. You can find more info on the forums at www.obdii.com.

09-06-2003, 07:50 PM	#10
Synx Newbie Join Date: Mar 2001 Location: Atlanta, Georgia Vehicle: 2003 Subaru WRX Posts: 13 My Photos: ()	I have made such a device, its powered by a AM186ED microcontroller, using a full demo board so its got two built in serial ports, some flashrom for saving the embedde software on it etc. Anyways i did the entire project my self using this board and a 320x200 pixel SED1330 controlled monocrome graphics display. It currently only works with the ISO9141-2 hardware standard(almost all JAP spec cars, ie Nissan, Subaru, Toyota, etc). The ISO standard is really easy to design the hardware for because its basicly a serial link with slightly modified logic leves. Instead of the -6to-30V for a logic 1 on RS232A its +12V, and instead of +6to+30V for a logic 0 on RS232A its 0V. This is easy to convert and because you really need to optically isolate the connection anyways you can use the optoisolators to do the level shift and inversion for you. I would recomend purchaseing the ISO 9141-2 document if you are really serious. You are also gona need to learn the iirc. SAE J1978 OBDII protocal to use for communication. Basicly the SAE protocal is used ontop of the given hardware levels, ie ISO 9141-2, PWM, or VPW. Also in the very near future there will be a new standard called CAN. I would also recoment you purchase the SAE J1978 document. Both can be downloaded in PDF format for around $40 us iirc. Again this is only for ISO specific cars, so this will not work in Fords etc. I have not designed the hardware for the two other standards so im not sure how it could be done. BTW may i suggest the MAX232A chip to do your line level conversion hint hint if your just gona use the PC serial hardware. Okay that was long and prob very confusing, sorry i have a hard time organiseing my thoughts on matters such as these. Anyways i wouldn't mind helping much as i am going to be porting my software to win32 soon i think so i can so a very similar thing for my Subaru WRX, its going to be a 2x16 CHAR lcd to display things such as Engine Load, EGT Temps, Coolent Temps, Boost levels(not sure if this is possible yet), etc. Good luck and i hope what i wrote was understandable. EDIT: Side note, if you going to be using a PIC controller or BAISC stamp type microcontroller, you had better have a dedicated CHIP to do the house keeping on the OBDII connection. You will have a VERY hard time trying to get the BAISC or PIC controller to keep on top of the strict timing requirements for OBDII. If you do decided to go this route there are IC's such as a few made by ELM that will do all the raw OBDII communication stuff for you. You can find more info on the forums at www.obdii.com. __________________ 2003 WRB Subaru WRX 99 Nissan Sentra SE Cobal Blue (SOLD) P166 64Meg RAM ATI All In Wonder PCI 16Meg SB AWE32 Plug'n Play Linksys PCI NIC Western Digital 13Gig UATA-66 HD 5.6in Color Active Matrix TFT Screen AloneInTheVoid Last edited by Synx; 09-06-2003 at 07:56 PM.

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