Adding PWM J1850 support a a clone ELM327 OBD II adapter possible? - Page 1
Forum section: electronics / repair

author: poot36
author_rank: Frequent Contributor
timestamp: November 15, 2020, 12:42:21 am
content: I am wondering if I can add support for the PWM J1850 protocol to my Bluetooth ELM327 clone adapter? I have found a site with pictures of the inside of my adapter (under ELM327 fake):https://translate.google.com/translate?hl=en&sl=it&u=https://jucetize.weebly.com/obd-elm327-v15.html&prev=search&pto=aueand it shows a lot of unpopulated pads that I assume I would have to populate to get this protocol working. Is the possible or due to it being a clone the software on the micro would not support this protocol in the first place? It has a 24 Mhz crystal so I am going to guess that it is a STM32 based clone but I am not sure.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 15, 2020, 03:50:11 am
content: sometimes some connections on the obd connector are missing too .... if you know the main chip under the blob you may find some firmware, but you do know, it was emulated on different chip(s)I did find a very close copy of an original elm327 adapter, and i bought an elm327 v2 original chip, substitued it (the clone) and it works very wellsome elm327 in metal casing where very close to the original designs, up to 1.5 version youll get the chance to have 90-95% of a cheap copySimply buy an original elm, thrust me i have 8 clones (wifi, rs232, ftdi based an other usb chipsets)Some sellers say on Fleabay and Ali v2.2 versions, but when you do a software querry of the fw version they report 1.5

author: coromonadalix
author_rank: Super Contributor
timestamp: November 15, 2020, 03:51:42 am
content: https://www.carscanner.info/choosing-obdii-adapter/

author: poot36
author_rank: Frequent Contributor
timestamp: November 15, 2020, 07:19:16 pm
content: I do realize that the adapter I got was a clone and it does support the CAN bus as well as the L,K bus but not the PWM bus. I have traced out some of the pads with missing components and think it matches the schematic layout for the real chip in the datasheet. At some point I will try adding the components and see what happens. I did confirm that the micro runs on 5V so that rules out the STM32 I think. Torque identifies the unit as 2.1 with issues and the OBDI identifier app identifies it as 1.5 but passes all the tests except for one. I may have to get a forscan compatible one if my ideas do not work out.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 16, 2020, 11:33:19 am
content: the problems with clones when you do request the fw versions thru the at commands, the answers can be fakedone thing i saw, are the datastreams been unreliable in the clones for a long term applicationgood luck

author: poot36
author_rank: Frequent Contributor
timestamp: November 20, 2020, 03:57:38 am
content: Ok, I have traced out the circuit and it matches the one in the ELM327 datasheet except for the voltage switching that feeds Q2 and R8. I have also confirmed that the micro does run off 3.3V not 5V as I previously guessed. Not sure where the 5V goes. What would I have to change resistor wise in the schematic to get it to work off 3.3V instead of the original 5V? The transistors are generic 2N3904 and 2N3906 ones. I have attached a cut out of the relevant part of the schematic and a picture that I have marked up of the different voltage switching section to this post. It would be nice to figure out what components should go there to restore the voltage switching function.

author: daisizhou
author_rank: Super Contributor
timestamp: November 20, 2020, 05:21:20 am
content: Do you plan to make OBD II adapters by yourself?

author: poot36
author_rank: Frequent Contributor
timestamp: November 21, 2020, 10:55:55 pm
content: @daisizhou No i do not. I am just trying to modify the one I currently have to work with a older Ford car.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 22, 2020, 01:53:17 am
content: Buy a clone with the added switch on the back ...https://www.ebay.com/itm/Forscan-Elm327-Bluetooth-Wireless-Switch-Can-Bus-Scanner-Diagnostic-FORD-MAZDA/333357575111https://www.ebay.com/itm/ELM327-USB-OBD2-Modified-For-Ford-MS-CAN-HS-CAN-Mazda-Diagnostic-Forscan-Scanne/323851235842https://www.ebay.com/itm/ELM327-USB-Switch-for-Ford-Mazda-Elmconfig-FORScan-FTDI-PIC18F2480-500-kbps/302721457171

author: poot36
author_rank: Frequent Contributor
timestamp: November 23, 2020, 12:52:18 am
content: Well I added the components, I tied the junction of R8 and Q2 to 5V and I did not have a 22K ohm resistor for R10 so I used a 47K ohm one instead. I found all matching NPN transistors with a hfe of 170 and the PNP transistors I used two random ones with different hfe's. Now the Bluetooth will not show up or connect but the lights on the unit still flash like they did before the mod. Its it possible that the Amtec flux (from china) is conductive at rf frequency's? Got any idea why the Bluetooth is now not working? I wonder if I have to add the button and its associated components to get the Bluetooth to work?

author: poot36
author_rank: Frequent Contributor
timestamp: December 03, 2020, 04:02:15 am
content: Have confirmed the button and it's associated components are just for powering the unit on and off, not connected to the micro in any way. I think when I was using the hot air to place the components onto the board I damaged part of the bond wire connections to the chip under the black blob because some of the input lines I can no longer detect the reverse protection diode in them. I think it happened when I heard a pop and a resistor that I was not touching removed it's self from the board (suspect a air bubble under the epoxy blob expanded and vented out the side hence the pop). Oh well, I have ordered one that claims it supports the forscan software so we shall see what it is like (if it arrives that is).