ALDL Circuit Power Consumption

[robertisaar]

has anyone measured exactly how many mA a 2-transistor ALDL circuit(or even a MAX232 circuit if 2-trans info doesn't pop up) draws? i may have a very interesting lead on a fairly cheap convertor to convert it from serial to USB. it actually uses the same IC as the aldlcable.com USB ALDL cable.

it seems like a VERY simple circuit with few components that draw anywhere near a sizeable amount of power and i have heard an estimate of ~20mA or less before.

[IsaacHayes]

Not even 20ma. That is what the FDTI chip draws likely.

If the 2 transistor setup will run by stealing power from the serial port, it's going to not be a current issue. The issue would be running from 5V if that swing is enough for the FDTI serial interface to detect. I'd imagine it would be as that's probably how the aldlcable.com setup works. I doubt they have another IC to boost the power to the two transistors setup, however the FDTI ChiPi does have that 2nd IC to run the 12V+/- swing so it's at RS232 spec. I don't know if they tapped into that, but if they did, you could tap into the DTR I'd figure and it would run just fine.

I'd try the 5V VCC on the USB line to power the 2 transistors, hook the serial port for the gnd, and Tx and Rx and see what happens. If no good, then steal voltage from the DTR line.

It's not so much a current issue but a voltage issue (possibly not even an issue). You don't need much current, just voltage for the signal to be detected.

Perhaps ask FDTI what the minimum voltage swing on the Tx and Rx lines it will detect as a signal. That's the real question. If it will see 3v +/- as a signal you'd be good even with a low powered USB port or one that has voltage sag down a bit from 5v.

[DefEddie]

Getcha a Fuse Buddy.
Nifty little ammeter with a digital display,remove fuse,insert fuse buddy fuse,read amperage consumption. (max 20a or 30a I think)
I don't have a scanner for the OBDI stuff or I would plug in,run some logs and measure for you.
The Fuse buddy was only like $30 for mini fuses,I also have an attachment for my multimeter that reads the larger style fuses.

[IsaacHayes]

No need to put a fuse anywhere, this is a circuit and simply using a DMM in series will work, but the switching may be so fast that you won't register a correct reading.

Either way the current is negligible.

[DefEddie]

I figured it would be the easiest way to check voltage oncar without pulling pins.
My multimeter's min/max function has no issue with milliamp/millisecond transitions

[3400beretta]

1.21 gigawatts.

[IsaacHayes]

No pulling pins/fuses. This is a custom setup that we are building that plugs into the ALDL port...

DefEddie, do you have a Fluke? I'm not sure my el cheapo craftsman would read accurate with 8192 baud signal running through it going from positive voltage to negative constantly...

[robertisaar]

isn't it possible to calculate power consumption by knowing how much resistance there is in a circuit? at least theoretically?

EDIT: if someone could measure the resistance from one end of the circuit to the other, and punch in info in the third line, that would be great.

http://www.the12volt.com/ohm/page2.asp

[IsaacHayes]

Once again, over thinking... Get the ChiPi and just do it......

[robertisaar]

Once again, over thinking... Get the ChiPi and just do it......

planning on it...

was punching in numbers just for fun and looking at the 2 trans diagram, and figured that no matter what, the power is going through a 10K resistor. at 5 volts, that's 0.0005 amps. that is .5mA... i can't even fathom that small of a number.

[DefEddie]

Not a Fluke,same thing as the big $600 kit they have just rebranded and only $350.
I also have a fluke that does min/max though,just not the full kit with it.
I use the rebranded one more,it's got more function's than I can figure out including pulsewidth/duty cycle,infared temp etc..

[IsaacHayes]

What is it then? a Fuke? Fulke? LOL

Hmm. the pw and duty cycle stuff could come in handy for designing some things..

[DefEddie]

I say Fluke rebrand,I can't remember if that is correct or not for sure. Does Fluke make the Bosch?
The Bosch multimeter for "Hybrids" is the exact same thing I have without a kit,Mountain 8730 is the part number IIRC.

[Tbay99Venture]

Power requirements

Yes, you have the correct solution -- a transistor in saturation is going to be pretty close to zero volts collector-emitter drop. I don't recall off the top of my head what base-emitter vs. base-collector difference is to consider the transistor saturated, but even if the total drop across collector-emitter is 1/2 a volt that's still 4.5 volts across 10K ohms. Not much current at all.

Of course the TxD/Data signal path won't be taking any current from the "+12V" supply so the only one you have to worry about would be the Data/RxD.

(Regarding messages #8 & #10)

[robertisaar]

well, you just confused the hell out of me!

i'm building the serial portion at the moment, not going to solder it up yet until i get my nice leaded solder from china.