How to convert OBD2 cable to ALDL

[h4x0r Profile]

Here is a money saving tip. ALDL (OBD1) cables are selling for $65 but you can buy an OBDII cable for as little as $7 from aliexpress or ebay and easily modify it to work as an ALDL (OBD1) cable.

All you need is:

1 x Piece of wire
1 x Diode (1n4004) Common and sold everywhere for around 20 cents

These cables come with a Serial Communication chip 'CH340' and 'LM339' comparator chip. Simply solder the wire and diode in place as shown below and you will have a working ALDL cable for under $10

[Charlescrown Profile]

Can you let us know where you got it from and some way of identifying it. The problem I see is there are so many variants out there in the market place no 2 are the same.

[antus]

I think its a generic VAG KKL type, but yeah to get the right one? Its the same principal as the resistor + diode version here viewtopic.php?f=11&t=71&p=675 only the resistor doesn't exist in this one, its only the diode part of the circuit.

[h4x0r Profile]

Can you let us know where you got it from and some way of identifying it. The problem I see is there are so many variants out there in the market place no 2 are the same.

Here are 2 i have bought from different places which have the same electronics on the inside:

obd2-to-aldl.jpg (192.19 KiB) Viewed 1393 times

Anything with the OBDII or VAG-COM 409 such as the photo should be fine.

Anything with the FTDI chip (FT232RL) will not be the same as my photo but the same wire of connecting to pin 16 power for logic will probably apply also anyway.

current links:

https://www.aliexpress.com/item/1005003 ... lbxMDZLwPU

https://www.aliexpress.com/w/wholesale- ... .1000002.0

[MudDuck514 Profile]

Question:
Are these actually OBD1 vehicles with a 16-pin connector (sometimes referred to as OBD1.5?), or are they truly OBD2, with the ALDL connections too?

Mike

[antus]

They are OBD2 K-Line protocol, or KWP2000. But that chip is skipped in this example, its ALDL straight on to one end of R3 which is a direct connection to the CH340 RX pin, and the diode to pin 7 of the LM339 where the signal goes the other way back to pin 3 of the CH340. The LM339 KKL part of the circuit is not used at all, and is not connected car side when you plug it in. So it's essentially just a cheap OBD connector shell with a usb interface chip in it when used this way.

[SoullessShadow Profile]

I have the day off kinda today. So was going to attempt to.make one of these the only spare cable I had laying around had a ftdi chip and a LM393 chip that's only 2 output. But I'll see if doing it this way works on that too.

[antus]

Dont bother with the LM393 or any of the components connected to it. Just put the diode across its TX it's RX and opposite end of the line on the diode end to ALDL (like pictuted) Just keep in mind there is no protection on it. Should work in good electrical conditions.

[SoullessShadow Profile]

Ok so hopefully im on the right track here. In h4x0r example its wired up like in ALDL2.jpg from what I could tell.

ALDL2.jpg (164.5 KiB) Viewed 1225 times

My Cable is more like the one in ALDL1.jpg but has a RL chip not a BL but i pinned out the RX and TX pins and the go to the same places. I was going to try it like that? Anyone see something dumb im missing??

ALDL 1.jpg (107.25 KiB) Viewed 1225 times

[antus]

yep the aldl pin, the diode and tx and rx on the usb chip are wired the same.
you could pull off r1, r8, Q4, Q7 to electrically isolate the usb and the aldl from the LM393 part of the circuit as well. Dont expect functioning LEDs they're wired in to the KKL side of the circuit. But the ALDL data should flow through.