Getting ready to build serial to ALDL interface

[Blake]

Hey guys,
I was going to build my serial to aldl converter and saw this topic here:
http://www.syty.net/phpBB2/viewtopic.php?t=15625
Is this design working out OK? Sounds like I just need to disable hardware handshake(whatever that means).

I found this one also:

which looks a LOT like this one

The only real difference I see is that they have a 10k resistor between B(mode select) and ground. Has anyone tried either of these? I like to experiment but I also want to make sure I build one that works correctly and reliably(burn up my new laptop :wink: ).
Thanks so much,
Blake

 

[apun]

I used this one.

Alex

 

[jwaller]

yes Bill C just did a gp on some he built.....very good product and cheap as hell....

 

[Blake]

Thanks guys. Good deal on the products Bill put out.
I'm gonna try and build one myself though. I'm trying to learn how this stuff works as well. This should be an easy primer before I build my wideband kit.
Blake

 

[Sy#26]

I've done a bunch of ALDL interfaces, the MAX232 circuit works the best. The two transistor circuit will NOT work on some laptops and tends to be a lot more cranky in general. The various MAX232x chips use different external capacitor values - make sure the chip you wind up with uses the correct caps. The docs for your chip will give you these values.

Barry - Sy#26
Bangor, MI

 

[93 TY 2185]

I built this one.

But if you use the Max233 you don't need all those external capacitors.
I have some of these chips if you need one Blake send me an email.

 

[BillC]

yes Bill C just did a gp on some he built.....very good product and cheap as hell....

Ummm, I think you got me confused with InvisiBill. IIRC, he was the one making the scanner/Datamaster cables.

 

[Blake]

Thanks fellas.
I liked the simplicity of the Peter Gargano design and was just gonna do away with the 160 baud part of the setup.
The required uF rating of the capacitors was a concern as soon as I saw one used 3.3 and another used 10uF. I just ordered 3 of the max232's and enough stuff to make up 3 of them just in case I fubar something up. Stuff is CHEAP!! I only have like $13 including shipping for enough to make 3. Of course it is $13 worth of junk if I don't get the design correct. In the Peter Gargano design, is it OK to substitute a 10K resistor for the 1K0 resister in the circuit between ALDL terminal "M" and Max232 pin 11 ? Also, it didn't say if it was 1/4 watt or 1/2 watt. I guess it doesn't matter.
I ordered 10uF capacitors already. Thanks, Barry, for the tip on reading up on the material for the chip I get. It will be best for determining which capacitor will be needed. Just need a couple of those little prototype boards (cheapies from Radio Shack)and I'll start experimenting.
Please let me know what you think on the resistor preference.
Thanks so much,
Blake

 

[Blake]

Well, I looked it up and the number for the part I ordered is MAX232CPE.
Maxim makes it. Damn. Wish I would've ask you guys sooner. Looks like it would have been even easier if I had ordered the 233 with internal capacitors. The one I ordered needs nominal 1.0uF. I'll just use my 10uF capacitors and see how it does. I hate to waste the parts.
Please let me know on the resistor.
Thanks again
Blake

 

[93 TY 2185]

I used a 1K resistor for R1 and has been fine for 2 years now.
You can use 1/4 watt resistors, you are not drawing any current in this circuit.
I just looked up Maxims data sheet and the MAX232 uses 1uF Caps for C1-4.
The MAX232 will work OK just more soldering and it takes up more space.

 

[InvisiBill]

I've done a bunch of ALDL interfaces, the MAX232 circuit works the best. The two transistor circuit will NOT work on some laptops and tends to be a lot more cranky in general. The various MAX232x chips use different external capacitor values - make sure the chip you wind up with uses the correct caps. The docs for your chip will give you these values.

Barry - Sy#26
Bangor, MI

I don't think it's the "two-transistor" interface that's computer-specific. The cables I made using that schematic get power from the lighter plug. I believe it's the cables that try to get +12V from the serial port that don't always work. Of the 20 people using mine, none have reported to me that it didn't work... http://cable.invisibill.net/ doesn't really have anything new to add, but it does have some info about the cables I made...

 

[Blake]

Just an idea. Probably been done, but with the great expense of the ALDL molded connector(thus why it isn't included in many kits), why don't we do this? Jump off the ALDL's "M" terminal to get the data feed to the circuit, use the "A" terminal to get your ground(plus jump another good ground from the chasis shomewhere) and then... get one of those tiny black plastic boxes from Radio shack and run your "M", "A"/system ground, and 12 volt source into the back of the box. Put your circuit design of choice in the box. Mount an RS232(9 pin) cable plug on the front of the box. Then just mount the box to the bottom of the dash right next to the ALDL port. That way you just take any serial 9 pin cable and run it to your laptop's serial port. That way you don't have tons of wires all over the place and you can use any old 9pin cable to run from your laptop to your new diagnostic interface for your truck.
Just cleaner and the "size" of the circuit doesn't matter anymore as it is up under the dash and not hanging off your laptop's serial port.
I'm just starting to learn this stuff so please tell me if this is feasable or not. I'll give it a try if no one's done it yet. I do know that ribbon cable is good defense against crosstalk(advise came in the device programmer I purchased) so I may have to use 2/4 lead phone cord that is flat(ribbon).
Blake

 

[Sy#26]

George -

Using caps other than what the chip specs call for isn't gonna work. The various MAX232x chips differ in the caps used and are specific to the "x" designation.

Barry - Sy#26
Bangor, MI

 

[Blake]

Thanks, Barry.
You've saved me a LOT of headache. The spec sheet on the MAX232 said nominal 1uF. Sounds like I MUST use 1uF then. I thought that nominal meant that I could use a higher rated cap but not lower. Grrrr. I'll build it as far as I can and wait for the correct caps and resistors. Just need to order more caps. The local Radio Shacks around here are nuts. They want a $1 EACH for caps. They are only 10 or 12 cents each online. One more order and I'll have it right. Thanks guys for being so much help and not getting tired of my questions.
Blake

 

[InvisiBill]

Just an idea. Probably been done, but with the great expense of the ALDL molded connector(thus why it isn't included in many kits), why don't we do this? Jump off the ALDL's "M" terminal to get the data feed to the circuit, use the "A" terminal to get your ground(plus jump another good ground from the chasis shomewhere) and then... get one of those tiny black plastic boxes from Radio shack and run your "M", "A"/system ground, and 12 volt source into the back of the box. Put your circuit design of choice in the box. Mount an RS232(9 pin) cable plug on the front of the box. Then just mount the box to the bottom of the dash right next to the ALDL port. That way you just take any serial 9 pin cable and run it to your laptop's serial port. That way you don't have tons of wires all over the place and you can use any old 9pin cable to run from your laptop to your new diagnostic interface for your truck.
Just cleaner and the "size" of the circuit doesn't matter anymore as it is up under the dash and not hanging off your laptop's serial port.
I'm just starting to learn this stuff so please tell me if this is feasable or not. I'll give it a try if no one's done it yet. I do know that ribbon cable is good defense against crosstalk(advise came in the device programmer I purchased) so I may have to use 2/4 lead phone cord that is flat(ribbon).
Blake

I have my two transistor circuit housed completely inside the DB9 shell. I used CAT3 phone wire (4 wire) because that's what I had around. I have the blue pair for data and a ground, and the orange pair goes to the lighter plug for +12V and ground. You can (and some did) get mine without the lighter plug, and just run the orange wire to some +12V source. Then run the blue wire to the ALDL M (you could even use the back of the connector to keep it stealth), and either the blue/white or the orange/white to ground, either at the ALDL A, or somewhere else convenient. Mine literally looks like a regular serial cable with one end cut off and an optional lighter plug spliced on. Rather than have a box and a cable, mine is all in the cable and it's still no bigger than your regular serial cable would be... You can see it on my page, but it's a really crappy pic. I'll see if I can get a better one sometime...