MPGuino release one workspace

[mambrino]

Hi dcb, "the man itself"

It's just that (with the datasheets in hand) it's not very clear what the zener is going to do when provided with a low current. Is it going to stay at 5.1 V? 3 V? or 0 V? An ideal zener would keep the 5.1 V, but what about a real one? It seems (to me) that the datasheet is "silent" about this point.

Well, if the experience tells that it works, it's OK, so no more to say...

I wasn't pretending to criticise or offend (of course!), I just wanted to understand the circuit.

By the way, great work!

Many thanks!

Originally Posted by dcb

From my understanding, the zeners operate low on the "knee" at low currents, holding the voltage below 5.1 volts. It was tested and the injector'vss signals at the pin looked fine with an oscilloscope, as far as I can tell. The Zener is cheap, simple, and effective at forward and reverse voltage protection, and fairly common "normative?" practice.

If it aint broke why fix it? I tried a transistor circuit originally, didn't work the first time, and I want as many folks as possible to be able to get it working the first time. There's no reason an experienced person cannot embellish the interface or even the power supply or??? But my philosophy is simpler is better, especially with months of testing in many vehicles behind it and in lieu of a non-theoretical problem.

[dcb]

Here's a picture, at lower currents, the zener voltage is lower, so low current is not a concern from a protect the pin perspective. With 12 volts through 100,000 ohms we are in .1 milliamp land, which is apparently enough with the zener diodes specified and the atmega168 to make a clean signal (needs to get above 2.5 volts).

[mambrino]

Nice graph! If we take a look at the 5.1 (maybe?) curve, it's "obvious" that it gives about 5.1 at 50 mA, and about 5.0 at 10 mA, but it's less clear what happens at 1 mA. Maybe 4.5 V or 4.7 V? And at 0.1 mA, it's so close to the axis that's impossible to tell from the graph...

Anyway, as you said, "if ain't broke...". And if so many people have tested the circuit in reality, there's not much to object.

Originally Posted by dcb

Here's a picture, at lower currents, the zener voltage is (...)

[orange4boy]

Hello,

Just finished soldering my MPGuino kit from Fundamental Logic. Huston, we have lift off!

I have some reading to do to figure all this out but I'm stoked!

I also got a present in the mail from vtec-e. (a prince among men) A sweet digital vac gauge! I'll post it all soon with pics in http://ecomodder.com/forum/showthrea...ding-5540.html

So many gadgets so little time...

Thanks dcb, You rock!

[orange4boy]

Got everything set up and wired but it does not turn on in the car. USB hookup works. I get 12V and ground cont. at the board in the car but mpguino is blank

The machine comes pre loaded from spiffie yes? I don't need to flash anything if the program comes on with the USB hooked up or is that a separate program?

The instructions are not entirely clear on this for us non techies.

Thanks

[wyatt]

if you don't see anything, try pressing the center button a few times. It may just be that the contrast is off.

[dcb]

hi Orange, do you have usb and 12 volts connected? (just curious, probably wasn't designed for both at the same time)

If usb works, and 12 volts through the regulator circuit doesn't, then your onboard regulator circuit is funky. Take a voltage reading to ground on the other side of the diode, on the regulator input and on the output to help isolate the problem.

[orange4boy]

Getting .56V on the outer leads. Funny thing is that I'm getting continuity between the wrong leads from the RJ connector. Should there not be 12V getting to the regulator diode? the square one with the heat sink tab? Im getting 12v at the back of the female RJ on the opposite side to the one with continuity to the diode which points to a mistake in the instructions or a crossover phone cord. possible?

It's not the contrast for sure.

How would I rewire the RJ?

[dcb]

you should have 12 (ish) volts to the regulator, 5 volts out, and a ground. If no 12 volts then maybe a diode is installed backwards?

[orange4boy]

I have checked them several times and they are all correct as the instruction photos and board graphics show.





I have it hooked up in my shop now to a battery. I'm showing 5ish volts all over the place but no joy on the screen. How would I test if I got a bum diode? Or could it be a bad solder?