Simple One Transistor Circuit:
Aldl has a port for sending data and the RS232 on PC has a receive data pin (RxD) so the easiest way is to connect them directly but since each system uses a different voltage we should put a transistor between them .
The simplest ALDL interface circuit i could find consisted of one transistor and two 10k resistors it simply connected the data pin on the ALDL plug to the RxD(Receive Data) port on the RS232 on the PC through the transistor .
This circuit worked , but for some reason the response was slow , i couldn't make it work with a Usb-to-Serial converter , and on some PCs you can't take power from Pin4 so you have to connect it to 12v external power source (the resistor stays).Two Transistor Circuit:
Since the first circuit performance wasn't great and the whole thing was messy , instead of refining the first circuit i thought i should try a new design .
This circuit consisted of two transistors one connecting the "ALDL data" to "RS232 Receive" , the other connects the "RS232 Send" to "ALDL Ground" .
The Circuit Diagram :
Parts Needed:
- 2 2N3904 NPN Transistor
- 3 10K Resistors
- 1 1N4148 Diode
- StripBoard
- DB9 Connector
- Car cigarette lighter Plug
The Strip Board:
The ALDL interface circuit components soldered to board:
...and the ALDL circuit with all the wires connected:
a closer shot of the finished ALDL circuit:
OBD1 / OBD2 : On-Board Diagnostic system is the ECU's operating system OBD1 was implemented early 1980's to 1996 , OBD2 from the year 1996 to present.
ECU / ECM : Engine Control Unit / Engine Control Module a device used in modern engines to control engine's operation .
ALDL : Assembly Link Diagnostic Link is an interface for communicating with the Ecu developed by GM for pre-OBD2 ECUs.
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13 comments:
sir it is a nice and informative post indeed. I want to know which software to use with it. I am planning to connect the daewoo cielo engine with this kit.
Thanks and regards
Thanks, try using WinAldl its a great program you can find it here http://winaldl.joby.se/
sir,
Thanks for the prompt response. I have another question. Can db-25 port (printer/parallel) can be used by using pin 3 (RxD), pin 2 (TxD) and pin 7 (Ground). (found from http://www.geocities.com/vbmcomputers/pinout/)
Hoping for prompt response.
Thanks and regards.
Also another question. Is the ground you mention on the two transistor circuit, the car battery ground shorted with the aldl ground and db-9 ground
Thanks and regards.
Yes you can use the LPT(printer/parallel) Port in theory but not with the winaldl software , i can't find a software that supports this port , and the ground is not connected to the car's battery ground , its only between the PC's and ECU ground . what year is your car and what engine size do you have ?
I have a daewoo cielo dohc a15mf with 1.5 displacement. This engine is also analogous to opel kadett and vauxhaul astra.
I have another question i.e., if I use usb to db9 converter then is there need to install a driver for windows.
Thanks and regards.
Can you leave the diode out or is this really necessery?
I have all the parts but the local shop is closed :)
really want to try it now; allready made the first wire, did not work, misses the +12v line.
Hey Sander ,
Am not expert in electronics , so i don't know if it will work without the diode , but the one transistor circuit should work , try to connect the "DTR power pin" to the 12v from the car and 10k resistor .
I had too many problems when i tested this circuit , the location of the Data pin on the ALDL was different than i was told , i found it by trial and error , it maybe different on your car.
Usb to serial converters didn't work on my laptop , so i had to buy a PCMCIA serial card , which worked like a charm.
You can eliminate the ground link to the ALDL ,and connect the transistor's emitter and Pin5 of the serial port to the battery's negative.
Thanks Mafak,
Well I waited this long so I'll just pick up the diode now :)
I have been told that I need pin 9 or pin 7 of the OBDI connector; 7 could be the L line but that makes it OBDII? But then again, I've been hearing allmost only contradictions so don't know what to believe anymore. Isn't there a list of which pin to use per brand?
It is all getting way to complicated..
Will try above diagram; that will be the 4th interface cable I'm making. If that doesn't work I give up.
Thanks anyway!
Too bad, the cable doesn't work on my Daewoo Nubira 1.6 from 1999..
So a warning to all daewoo owners :)
You need special hard- ánd software.
Suggestions are still always welcome!
According to this website http://www.obd-ii.de/tech_com-uebe.html your car is OBD2 that uses the J1850-VPW protocol , so this circuit shouldn't work .
As I said, I hear a lot of different things :)
Another owned with exactly the same car, model, year and engine says it is ALDL.
Some other say ISO9141 (not the -2 variant) and some other say it is a complete unique system only used by Daewoo and you need a special Daewoo tool to read or reset the ECU.
I will take a look at the link provided.
Mind that I have a european car, I'm from The Netherlands so.
Thank you anyway for the quick responces.
Sorry for the dubble post..
A question just popped into my head: Do you know, or can you find a simple diagram (with transistors and diodes only) that supports the J1850-VPW interface?
All I can find on google are ELM232 interfaces. That's one step above my skills :)
thanks!
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