Last night a built an aldl adapter, sort of like the one here http://www.syty.huryde.com/html/electrical/aldl.htm (but using a MAX233, the transmit pin pulled high, switched to ground with a transistor), and today when I tried it out, WinALDL showed data only in the MW2, PROMIDA, and PROMIDB of the raw data table. What does that mean? The car is a 90 LO3, so I'm pretty sure it has a 1228746. If so, the ALDL doesn't require a resistor between A and B And the ALDL transmits 0 and 5 volts, not 0 and 12. Right? I'll keep working at it, but is there something obvious I'm missing? One last thing, on WinALDL, there's a box between the text Ver 1.09e and the configuration button. What's it for? It was showing 1 2 1 2 3 2 1 3 ... etc. Thanks in advance.

Did you build it like this? It's really simple to build and works great.

Steve

Well, I tried one like it. I built it a few times, and it didn't work, so I figured, why not try an old rs232 circuit I had built, with a little modification. Maybe my laptop knows real rs232 from pseudo rs232? So here's what I tried:

oh yeah, if it matters, I tied the following pins on the 233 together, like the data sheet shows (they might be internally connected anyways): 12 to 17, 11 to 15, 10 to 16

The little flashing box is showing bytes received - normal operation would have 20 flashing about once per second.

I built the cable a few times with various less results (would get a few bytes like you) - then I decided to stop trying to build the circuit into the DB9 - I bought a small project case with pc board, and put the components on the board - worked the first time and never had any issues.

Just a reccomendation, but I'd look at building the circuit on a tiny PC board (I've done this before, works REALLY well) as suggested above, and to further it - use an RJ45 connector underneath so you can use a flat RJ45 cable along with an RJ-45 to DB9 adapter. Place the circuit with the jack underneath your dash somewhere and hook +12v into it from the car. The serial port isn't the most reliable place to get your power from as I've found out. Some laptops MIGHT be able to use it, some might not. Rather than chance it, just go ahead and use car power from it.

Also, if the box that has the numbers in it is flashing *red* then you're not getting clean data. It should flash the number "20" with a green background (that's a solid 20-byte data stream.

What ECM/vehicle are you working with..? Does it have a digital dash by any chance?

I used the one transistor cable for a while. Had to give it 12v from the car. (Couldn't get the serial port to provide power) I was using Winaldl.

I then switched to Moates s/w and bulit the MAX 232 cable interface.
I'm now getting a full set of data every .2 secs reliably. I tried updating at .1 secs, but it dropped a few packets.

I left out the serial port power diodes, but included the optional signal diodes near the bottom right corner of the schematic. It works very well with my 87 165 ECM running $6E.

ZZ, MFaulkner has a lo3 tbi and the ecm is a 160 ecm so I don't think he will have a problem. I also have an lo3 tbi and all I can say is that all us tbier's wish we could record data faster as the rest of our fbody brothers can do.

Steve

Yeah, it flashes red. I guess that's part of the problem! Now that I can be sure it's the cable's fault, and not any setup on my laptop, I'll just have to tinker with the cable's circuit. Thanks, I wasn't sure where to start fixing.

The car I'm working with is a '90 formula. It's a 305 tbi, so I'm assuming it has the 1228746 ECM, and no, it doesn't have a digital dash (Out of curiosity, what affect does the digital dash have on reading from the aldl?)

Thanks for the help! Anything else I should know?

The ECMs that support a digital dash have a 5 byte output unless in ALDL mode with a 10k resistor, then they change to 20 bytes. I believe the 5 byte output provides the estimated mpg - not sure if there are other functions as well.

Well, I'm very pleased to report that I got the cable to work. I ended up using the circuit I posted earlier, but I removed the transistor, and fed the aldl data through a 10k resistor into the max233. I also switched from using the serial port as a power supply to using the car's 12 volts (where a cig. lighter once was, a power plug now resides). Now to figure out what all those numbers mean!