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16  Using Arduino / General Electronics / Re: The right parts to make my project smaller.... on: August 22, 2014, 08:41:17 pm
I understand that amps play a role to but I also said that I am using and ATMega328P which to the best of my knowledges keeps the amp limited to an extremely low number.

Exactly. To the best of your knowledge, which from what you have said here is incomplete.

The Arduino does not limit current. The voltage and load limit current. Unless your load would draw more current than the regulator can handle, then the voltage will drop from overload.

"... amps play a role..." Yes, that is a very important number. Perhaps your load is only drawing 20mA, and you are using a TIP120 merely because it is what you had on hand, or because you didn't understand that they are overkill for your purpose. You have indicated that you don't know how to select a transistor, after all. Or perhaps you are running at the limit of what that transistor can handle. Those two situations would necessitate entirely different answers.

We are actually trying to help you. You are a free agent, do what you wish.
17  Using Arduino / General Electronics / Re: Piezo Horns for swim race starter - flyback diode ? on: August 22, 2014, 08:34:17 pm
You'll need a resistor across the piezo, or the 22uF capacitor will never charge and so the piezo will still be getting pulsating DC.

The toneAC library will drive a piezo differentially from two pins, removing the need for a DC blocking capacitor and equalizing resistor.

From the page:

The library is named toneAC because it produces an alternating current (AC) between two pins. The ATmega's PWM takes care of this so the accuracy is exact. When you send a tone to a speaker with the standard tone library, the loudest is at 50% duty cycle (only on half the time). Which at 5 volts, is like sending only 2.5v to the speaker. With toneAC, we're sending out of phase signals on two pins. So in effect, the speaker is getting 5 volts instead of 2.5, making it nearly twice as loud. The sound quality difference has to do with allowing the Arduino's PWM to take care of everything and careful programming. Longer piezo life happens because instead of driving the transducer disc only ever in one direction (deforming the disc and reducing sound and quality), it drives it in both directions keeping the disc uniform.
18  Using Arduino / General Electronics / Re: If the flyback diode is "really" the wrong way round... on: August 21, 2014, 01:33:50 pm
Is there still a question there? The schematic is rather abbreviated, so I'm not certain if you've answered your own question.

In case anyone else is still wondering, in the case of an H bridge, the diodes go across the driver transistors, rather than the motor coils.

Like this:
19  Using Arduino / General Electronics / Re: Piezo Horns for swim race starter - flyback diode ? on: August 21, 2014, 01:26:11 pm
It is not a wise idea to feed a piezo with pulsating DC. It may damage the piezo.
20  Using Arduino / General Electronics / Re: The right parts to make my project smaller.... on: August 21, 2014, 01:16:44 pm
Okay well whatever I'm done, It works the way I have it, it has been working for the last month so i;m not going to change it. The pins are set to input_pullup, i may be a newbie but i'm not completely clueless.

I reached out to an old high school buddy who I haven't talked to in years, gave him the same explanation I posted here and he rattled off half a dozen parts I could check out on

I think I will steer clear of the forums for a while, It seems that one can't even be general in general section. To many people on here are more interested in there own ego's then the topics at hand. To many people think that every question need super-complexities in order to be valid and will make it a point to show off what they know and point out what you don't instead of answering a question. 

Yes, you should go with the first person that gives you an answer based on incomplete information. Don't bother with the people who actually try to help by first asking for clarification.
21  Using Arduino / Project Guidance / Re: Arduino 5V regulator is too hot on: August 20, 2014, 04:40:30 pm
The MC34063 is a very easy to find, cheap buck, boost, or inverting switch mode regulator. In fact, I can go to the local dollar store and buy tiny cigarette lighter socket 12V to 5V USB phone charger/adapters for... a dollar each.

The chip uses an internal switching transistor good for 1.5A switching, 750mA output current. An external inductor and shottkey diode and a handful of other parts are needed, but the lighter socket adapters have those already. Chances are, any cigarette lighter socket adapters use the MC34063.

You can check the part values, but I believe they already have current limiting set to 500mA. I'd use that to power the charger, and use a separate regulator to power the Arduino.

I like this calculator for the MC34063 because it allows you to specify an input voltage range. You need to figure it out as the middle of the voltage range, and percent variation.
22  Using Arduino / General Electronics / Re: 4 diode rectifier bridge on: August 20, 2014, 04:29:37 pm
Yes, those two circuits are the same.

No, there shouldn't be any problem supplying that with AC or DC, long term. The only thing to keep in mind, besides the fact that you lose 1.4V either way, is that 12Vdc nets you 11.6Vdc, but 12Vac nets you 12Vx1.414 - 1.4V = 15.6V.

Because 12Vac is about 17V peak, and the capacitors after the bridge charge to the peak voltage.

That is an electron microscope image of a piece of paper. I cropped that out of your original image. Heh, heh....
23  Using Arduino / General Electronics / Re: 4 diode rectifier bridge on: August 20, 2014, 02:42:05 pm
Well, I can see elementary particles in your schematic.


What I'm trying to say is, please resample your schematics to something maybe 800 to 1000 pixels wide, tops.
24  Using Arduino / Project Guidance / Re: Arduino 5V regulator is too hot on: August 20, 2014, 11:58:28 am
Not to mention the Arduino uses a linear regulator, whose output voltage will decrease as you draw more current.

Not true. A linear regulator will continue to supply 5V until you go over some limitation. The NCP1117 used on the Arduino Uno is rated at over 1A output. However, with 12V coming in, and 550mA coming out, that is around 3.6W. A lot for such a small package.

I agree with the rest- use an external switch mode regulator. But I would never use a regulator at 90% of its rated current. Use one that is rated for double what the circuit needs.

But - is this going to drive motors? Are you taking stall current into account?
25  Using Arduino / General Electronics / Re: I'm total noob pleasehelp (transistor) on: August 20, 2014, 09:32:01 am
Looking at that blog post on Make Magazine's site, I have to say that I have been very disappointed in the way they publish schematics.

This one is half pictorial:

This one is horribly confusing:

This one has only one Vcc and one Ground connection, and a mess of interwoven wires:

All miss the point of a good schematic diagram - make the circuit clearer and easier to understand.

Here is some good advice on drawing schematic diagrams:

Your schematic should NOT look like this:

Because it isn't clear that the polarity of the electric eel is incorrect.  smiley-razz
26  Using Arduino / General Electronics / Re: Transistor & MOSFET's are so complicated on: August 20, 2014, 09:15:58 am
Do you know Ohm's Law? When it applies, and when it doesn't?

Kirchoff's current and voltage laws?

Do you understand diode junctions?

You need the basics, first.
27  Using Arduino / General Electronics / Re: I'm total noob pleasehelp (transistor) on: August 19, 2014, 01:17:46 pm
Learn to draw schematics. It isn't that difficult.

Trying to amplify what?

Why are you using a car charger? What are you trying to accomplish?
28  Using Arduino / General Electronics / Re: What is a calabrating battery type called? on: August 18, 2014, 05:54:35 pm
Weston cell. I'd forgotten the name, too.

Pretty amazing, Insanely high accuracy 1.01830V @ 20C.
29  Using Arduino / General Electronics / Re: Old Computer Power Supply on: August 18, 2014, 05:40:33 pm
OK. Without being there to try some things, I'm not sure what else to suggest. Except maybe stick a scope on the outputs and see if any of them jump up substantially above what they are supposed to be. in normal use, most or all of the voltages will be loaded.
30  Using Arduino / General Electronics / Re: Why are there so many more N-Channel Fets available then P-Channel? on: August 18, 2014, 09:15:55 am
MarkT nailed it in response #7, electron charge carrier mobility versus hole charge carrier mobility.
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