ALDL Circuit Power Consumption

[Tbay99Venture]

Current load

Sorry I didn't organize my posting better. The aldl website gave a link to the 2-transistor schematic. I assume that's still what we are all talking about. Their page that had that link said they are just driving the transistors into saturation since the data rate isn't too high. So their circuit doesn't care much about a particular transistor type or resistor value.

As long as they're doing that and have spec'ed high resistors you are spot on to take the entire voltage drop across that resistor as they way to figure out the current load it will pull. And it's not a big number if you're using 50K ohms.

Did I do a better job this time around?

[robertisaar]

Did I do a better job this time around?

sounds fancy, confuses me though... i'm not much of an EE.

[robertisaar]

it seems i have an update, although not a good one...

i started putting it all together yesterday, finished it and i got nothing... the only way i can get it to pass the Datamaster ALDL test is to use a jumper wire on the Tx and Rx lines...

so that tells me the USB convertor is not the issue since it seems to transmit and recieve at 8192 baud, just not through my circuit... i'm going to have to go to my brother's house and borrow that desktop for a few minutes since it's the only thing that i know of that still has a serial port...

and if someone has a tip on how to test a transistor, feel free to let me know. resistors and diodes are easy enough to test, but i actually don't even know what a trasistor does...



using that diagram, i came up with this:

http://www.robertisaar.co.cc/web_images/aldl_circuit.pdf

and have no idea where i went wrong...

[robertisaar]

another update...

i was playing with my multi-meter and eventually got around to testing the diode... when i run the leads normally on the one thats already on the board, i get ~.555V when on the diode test. i figure that's fine since i get roughly the same result with my other 9 that i have sitting around. then i reverse the leads. on the ones that arne't being used, i get nothing, like i expected. but on the one that's on the board, i got ~.600V... so i thought, "hey maybe the diode is bad", so i desoldered that one out and soldered in a new one that i JUST tested and confirmed as good. now i still get the same result of .55V normal and .60V with the leads reversed...

i'm thinking this may be my issue?

and another thing: from what i just read, transistors are basically pairs of diodes in one package? and i would test them the same way?

[pocket-rocket]

Transistors are electric switches. You put a .7v difference between two leads and the other will conduct electricity if memory serves me correctly. One of the three leads will be a common between the one that take the .7v difference and the one that turns on.

[robertisaar]

so it's like a relay and a diode mixed into one device? whoever came up with this 'lectricity magic sure did think ahead...

getting new transistors in the morning and hooking it up to my old P4 desktop that still has a serial port.

[Tbay99Venture]

Transistor circuits

Per your first posting, that circuit should be pretty easy to test with just DC measurements. I think they stated on the web site where it came from it would have no trouble handing the required baud rate so if it works at all it will work at the rated speed.

It's easy to get the transistors mis-wired. Often the pin diagram specifies viewing the device from the bottom with the leads coming towards you. Here's a way to DC test:

Hook the circuit up to 12V. (Probably even a 6V lantern battery would do if it's easier to work with that at your bench.)

To test Q2, jumper the DATA line to ground and you should see very close to whatever is your DC supply voltage at the RxD line. Now jumper the TxD line to ground and jumper a 10K resistor from the DC supply line to the DATA line. You should see close to zero volts at the RxD line. That shows Q2 is OK.

To test Q1 keep that same jumper resistor from the DC supply to the DATA line and measure the DATA with TxD grounded. It should be close to the DC supply voltage. If that test passes then connect the TxD to the DC supply line and you should see the DATA line drop to close to zero volts.

Hope that helps.

[Tbay99Venture]

another update...

i was playing with my multi-meter and eventually got around to testing the diode... when i run the leads normally on the one thats already on the board, i get ~.555V when on the diode test. i figure that's fine since i get roughly the same result with my other 9 that i have sitting around. then i reverse the leads. on the ones that arne't being used, i get nothing, like i expected. but on the one that's on the board, i got ~.600V... so i thought, "hey maybe the diode is bad", so i desoldered that one out and soldered in a new one that i JUST tested and confirmed as good. now i still get the same result of .55V normal and .60V with the leads reversed...

i'm thinking this may be my issue?

and another thing: from what i just read, transistors are basically pairs of diodes in one package? and i would test them the same way?

That (transistor internals) is why your in-circuit readings of the diode aren't working out. The little arrow in the transistor symbol is there to indicate it's like a diode from the base (center lead in the diagram) to the emitter (lead that goes to ground in the diagram.) You're testing the diode in the transistor when you reverse the test leads, hence the 0.55V reading.

For the type of transistors you have the testing should show readings between 1/2 to 3/4 of a volt with the for base-collector and base-emitter measurements and "nothing" when measuring between collector-emitter as well as "nothing" when you swap the leads in the measurements above.

Wow, that sounds confusing! I'm not sure all meters use the same color convention on the test leads or I'd try and describe it that way.

These tests would have to be done on the transistor out of circuit.

[robertisaar]

somwhat good news to report:

the tests still all fail miserably.

but on a hunch, i decided to go hook it up and try it anyway.

it works... kinda.

it takes maybe 1/4 second to connect(considering how complex of a connect command i have, that's a good number), then it will display between correct and non-correct data continuously. sometimes TP will pick it up as a checksum error, but most of the time it didn't. i eventually stated moving my whole board around and at one place it displayed data PERFECTLY at a rate of like 8 frames/sec for a good 15 seconds...

so this thing definitely can work, but something is still funny with the circuit... i did test both transistors before hooking them in, both passed with good numbers.

now to figure out WHY it will alternate between a good frame and a bad frame... i MAY need to adjust the port timing settings, but i'm leaning more toward funky soldering since holding it perfectly still in one spot was working(until i moved it and couldn't get it to happen again).

any ideas?

[Tbay99Venture]

Circuit tests

You could try looking at RxD with a voltmeter while DATA is jumpered to ground. Now wiggle some things around and see if the meter shows a change.

Likewise for grounding TxD and looking at DATA while wiggling the components and joints.

[robertisaar]

messed with it a few minutes ago. using default port settings:

TPV4 doesn't show the erronious data, but it does add to the packet error count(and i only managed a average of 4.4375 correct samples per second, with a target rate of 10 samples per second)...

in 51 seconds, TPV5 recognizes 5 errors with a 50ms timeout, but if i had to estimate, then about half of the samples were junk. with a 100ms timeout; in 49 seconds, TP recognizes 4 errors, though half of all of those samples were junk as well...

i'm not sure what this in indicative of. is it possible i need to add a capacitor or diode somewhere in there to attempt to smooth out something? i ask due to what i found here:

http://www.saturnwiki.net/index.php/ALDL1

i never knew diodes could be used to essentially clean up a signal.

maybe my macro skills suck... my connect macro consists of the mode 8 macro 3 times, pause, mode 8, pause, mode 8, pause and then the send data macro.

my monitor macro consists of the mode 1 send, mode 1 reply, then a pause.

but this wouldn't really explain why TPV4 would recognize/generate faults as well...

[Tbay99Venture]

Protocol vs. electrical interface

Both those circuits look like they would be totally happy between the OBD_ and a USB or RS-232 serial connection. So what I'm getting at is if you knew the electrical part was OK by running it without errors with a true RS-232 serial port you could also be confident it works OK with the USB serial.

With those doubts out of the way you can zero in on the right protocol, macros, etc. But if the desktop or whatever PC that has a true serial port has problems with the interface present and doesn't without it then you know it's not your macros!

Hope I'm not just adding noise to your discussion.

[robertisaar]

You could try looking at RxD with a voltmeter while DATA is jumpered to ground. Now wiggle some things around and see if the meter shows a change.

Likewise for grounding TxD and looking at DATA while wiggling the components and joints.

just tried this, couldn't produce a noticeable change no matter what i moved.

had to swap the leads to get any kind of reading for one of them. one came up with .75M Ohms, and the other was around .3XXK IIRC...

[robertisaar]

Both those circuits look like they would be totally happy between the OBD_ and a USB or RS-232 serial connection. So what I'm getting at is if you knew the electrical part was OK by running it without errors with a true RS-232 serial port you could also be confident it works OK with the USB serial.

With those doubts out of the way you can zero in on the right protocol, macros, etc. But if the desktop or whatever PC that has a true serial port has problems with the interface present and doesn't without it then you know it's not your macros!

Hope I'm not just adding noise to your discussion.

tried my one desktop with a serial port in tests and couldn't get ANYTHING to happen. can't exactly haul it out to the car though to test it, not to mention it's being a bit flaky already.

[Tbay99Venture]

Circuit readings

Looks like my suggestion was vague. I meant that these should be voltage readings not resistance. With the circuit powered by a battery but not connected to a car or PC.

I'm pretty sure I've got parts & similar transistors to build one up. I'll try and do that to list voltage measurements.