The cable itself has been working flawlessly since last october. I built it based on the max232 circuit.

I was logging yesterday, and the data kept freezing, but when I restarted ecm852 it would work fine again.

I tried it again later last night and it wouldn't work at all.

I tried it on two other laptops and they don't work with it either.

I tried it on my desktop and it works perfect.

Went back to the laptops to try them again, and nothing.

My thoughts are that it has something to do with the cable drawing more corrent than the serial port in the laptops can supply. Any other thoughts for me?

Tonight I will probably solder in an external power supply for the cable and see what happens.

 

Still nothing after I soldered in the 12+ feed from my car directly to the regulator input. Do I also need to pull the voltage regulator ground from my car?

Here's the diagram I'm using:

Any ideas?

 

Anyone?

 

Well, I guess I'll let everyone know what the problem is when I figure it out.

 

I have had trouble with data logging if my laptop battery gets below 50% charge, it will only display partial data.

Have you tried the 2 transistor cable? I couldn't get the max 232 to work for me but the 2 trans works like a champ. I have run 12V to a blank pin in the aldl and power the cable from there,

 

I just ordered up fresh parts for the max232, I'm gonna try rebuilding it from scratch. Some of my solders were close before, maybe it got a voltage spike and arced for a moment...

If this doesnt work, I'll try the 2 transistor circuit. Does that one work with the 8192 baud, or just the 160?

 

Works at 8192 BAUD

 

Thanks for the help Morley, I'll let you know how it turns out

 

UPDATE:

The program I was using to test my cable wasn't accurate, would say it passed with nothing connected to the com port.

Made a new max232 circuit, wouldn't work at all again.

Just made a 2 trans circuit, it is sending and recieving the echo response, but will not connect. If I quickly and repeatedly disconnect and reconnect the data wire, the laptop will recognise different hex bits coming in. So, I think the cable is good.

I tested the data output on the 730 and it is outputting 4.8v like it should. But, it isn't alternating or fluctuating at all. Is this normal? Does it sound like the ECM is shot?

I don't need the 10k resistor between pins A and B to read the data stream, do I? It's a 7730 ECM out of a 91 camaro.

HAve also ran the rs232 port thru a self diagnostic test, it passed it without errors.

 

No, you don't need the 10k resistor with the 730.

The "self test" for the serial port is dubious at best. Try hooking a serial mouse or other serial device to it and see if it works.

Also, what laptop are you using?

 

It's a compaq armada 7350md

I'll see if I can dig up an old serial mouse to test it with.

I haven't tested the other laptops with it yet, that'll come later if I dont have luck with this one.

I've tested all the switching modes for the serial port, including "hardware", X-on, X-off", and "none". I've also played around with all the buffer levels to no avail.
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I think the transistors I got are the wrong ones.

They are NPN transistors, but they are larger, require at least 2v to switch on, and I don't think my circuit can provide the needed amperage to forward bias the collector and emmiter.

I tried changing the resistor values from 10,000ohms to 1500 ohms to raise the available voltage up some, but it didn't work. Probably due to the higher amperage requirement or these transistors.

EDIT: Here's the datasheet for the ones I'm using. http://support.radioshack.com/suppor...oc19/19987.htm

From what I can make out of it, it looks like I need 20mA to forward bias it, and then 10mA to sustain the connection. So far as I can tell, the circuit draw is only 1.229mA continuous.

Just for kicks, here's the datasheet for the 2n222a. http://rocky.digikey.com/WebLib/On-S...a/P2N2222A.pdf

The "ON" and "OFF" rating for these is measured in nano and micro amps and volts, as compared to milliamps and millivolts.

Oh well, maybe I can waste all next weekend on this too

Tomorrow morning I'm planning on taking some measurements on the active circuit to see where I'm "actually" at with the different components. I suspect that I'll be ordering the proper transistors though, since nobody carries them around here. I'll keep an update going here if I remember to.

Thanks again Morley,
Matt

 

I was able to get the right transistors from Ratshack...once. They have no "standards" when it comes to stocking it seems.

For power for the 2 transistor cable I ran a wire from my cig lighter to a blank pin in the ALDL (got extra pins from junkyard) so the laptop doesn't have to power it and I don't have to have an extra wire going to the lighter externally.

 

Not a bad idea, I just might have to steal it

I'll check the radioshacks in the next town over on my way to school tomorrow. Maybe I'll get lucky...

 

New transistors, tested all components and they all work.

Tested data line at ECM again, 4.95v. Tested it with the aldl connector hooked up, it drops to .65v. Is it designed to do that, or do you think my driver is fried in the ECM, and can't supply the needed amperage, so it's dropping the voltage way down?

Oh yeah, external power source getting battery voltage, and pulling from same ground that ALDL connector on car is using. I'm soldered in directly at the ECM instead of using the factory ALDL connector.

Laptop running off house power currently, not battery power.

 

As a stab in the dark...try reversing the diode, might be in backwards (I know I did that the first time).