ALDL Circuit Power Consumption

[robertisaar]

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.

electrical stuff at this level > ME!

i'll see what i can do with a few jumper wires and my portable battery jumper thingy.

[robertisaar]

more news:

i decided to go see what would happen if i gave the circuit +12V instead of +5V from the USB... i disconnected the USB plug, used two jumper wires to give it 12V where there was normally 5V and tried to connect... couldn't get any kind of connection to establish.

so i removed the jumpers, plugged the USB Power Only cable back in, and it would connect, although with the same crazy data.

then i decided to bypass the 10K resistor going from +5V cable to the next step in the circuit... now i can't get any kind of response to happen...

i just killed a transistor, didn't i?

[Tbay99Venture]

Cooked?

I thought the USB spec would limit current to 100mA so the transistor should have been OK. But if nothing is happening then perhaps it got toasted. You can check with your diode checker without removing the transistor. (Nothing else connected to the circuit.)

Assuming this is Q2 we are discussing you should see the 0.5 to 0.6 reading between the base lead (one wired to the DATA line via a 10K resistor) and the lead that goes to ground (emitter) and also between the base and the one that goes to RxD (collector.) Now swap the meter's red and black leads and do the same tests and you shouldn't get a measureable voltage.

Lastly, you shouldn't get a reading with either meter polarity between the collector (RxD) and emitter (ground.) If you do the transistor is shorted.

You can compare this to an unused transistor just to make sure.

[robertisaar]

that may be due to me having the jumper hooked up instead of the USB line... and USB spec is 500mA IIRC...

fuck, i'm about to go lookup what it will cost me to build a MAX232 circuit...

[Tbay99Venture]

Yes, USB can give up to 1/2 amp, but only if a device registers for higher current, otherwise it's 100mA. Funny thing is Linux always enables high current and so you can charge your phone easily from a Linux PC but need the driver if your going to use MS-Windows.

[robertisaar]

well, it's going to cost me $3 for two MAX232 ICs shipped... and then all i need after that is 4 capacitors and 1 1K resistor. should have went this way from the start.

[robertisaar]

i modified and recreated the diagram from Techedge to come up with what i need. i have to ask: is there enough difference between a 1N914 and a 1N914A diode to make a difference here? i can't find any kind of comparison info on the internet to compare differences, if any...

http://www.robertisaar.co.cc/web_images/max232_aldl.pdf

[Tbay99Venture]

Diode grab bag

Either diode would be beauty. From the Maxim website pin 12 is just the outbound TTL signal. The diode allows the Maxim to pull the voltage down when writing a zero bit but otherwise isolates the signal driver (float means the car pulls the line up and a one bit is the result.)

http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1798

Maybe the true +/- voltage swing from the Maxim on the RS-232 lines will cure the data errors you've been seeing. The simple transistor circuit would only be 0 to +DC and might have left things too close to the noise level for the USB serial device.

[robertisaar]

"Either diode would be beauty."

"Maybe the true +/- voltage swing from the Maxim on the RS-232 lines will cure the data errors you've been seeing. The simple transistor circuit would only be 0 to +DC and might have left things too close to the noise level for the USB serial device."

ok, i understood most of that, which is exactly what i was looking for.

[Tbay99Venture]

Apparently it's a been there/done that

I was sifting down a different thread and see that the two-transistor circuit doesn't have good history:

http://60degreev6.com/forum/showpost.php?p=232448&postcount=19

http://www.andywhittaker.com/ecu/aldl_hardware_cont.htm you want the MAX232 circuit. the 2 transistor never worked for me. Back to the topic at hand - If I posted a pic of my oscilloscope connected to the O2 sensor, would anyone be able to tell if it's working or not? I'm getting wierd readings.....

Where was that when this whole thing started

[robertisaar]

actually, ryan hess has roughly the same thread and his eventual dismisal of it on TGO. i just find it odd that a commerically manufactured 2-transistor circuit worked perfectly for my laptop before, but now i can't replicate it myself...

oh well, the 232 is on the way. then i'll just go to radioshack, pick up 4 capacitors, 1 16-pin socket so i don't have to solder directly to the chip and i'll be done with it.

[pocket-rocket]

well, it's going to cost me $3 for two MAX232 ICs shipped... and then all i need after that is 4 capacitors and 1 1K resistor. should have went this way from the start.

MAXIM will send you 2 free chips per "sample" (free shipping even ), but at least $3 isn't bad. You could have come down here, I've still got 4 chips left over from the 3 "samples" I ordered some time back when I did my whole ALDL deal, I would have more than gladly given you 1 or 2.

i have to ask: is there enough difference between a 1N914 and a 1N914A diode to make a difference here?

No, they are completely interchangeable for something like this. Day late and a dollar short

[robertisaar]

MAXIM will send you 2 free chips per "sample" (free shipping even ), but at least $3 isn't bad. You could have come down here, I've still got 4 chips left over from the 3 "samples" I ordered some time back when I did my whole ALDL deal, I would have more than gladly given you 1 or 2.

i read that somewhere online as well, but the 232s are marked as NOT SAMPLEABLE for now.... i'm not sure when they did this, but yeah, at least i got them cheap.

[robertisaar]

leaded solder has arrived... now i just have to wait on the damn 232s...

[robertisaar]

after much time spent fucking around with the post office, i got my 232s today...

Maximum Cheap ALDL cable is a success...