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1  Using Arduino / General Electronics / Re: Power Supply questions on: July 22, 2014, 12:01:32 pm
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The leakage current is under 1mA, which means the outputs could be floating
at mains voltage levels if not tied to PE somewhere - recommended unless you have
a genuine reason not to.
I would get shocks from my bench supply because i leave  Jumper wires sticking out of the Ground rail on the breadboard. Every now and then my elbow would brush across one and i would feel a sharp stinging sensation. It took a few times  to realize what was going on.  Probing V- wrt ground shows about a 30 volt difference :/.
2  Using Arduino / General Electronics / Re: Power Supply questions on: July 22, 2014, 11:37:02 am
I would agree with Fungus. "V-" is the DC negative return path which is probably isolated from earth ground . Earth ground should be connected to mains grounding system for safety. In any case Probe it to be sure. Rarely, these cheap SMPS power supplies are dual voltages unless specifically marked. If you use Vin, you best be absolutely sure of your polarity.
3  Using Arduino / Programming Questions / Re: I just do not understand these output voltages on: July 22, 2014, 11:10:47 am
a schematic and picture might be helpful. what value resistors are you using? its always smart to initialize your inputs as well.
4  Using Arduino / Project Guidance / Re: How rugged is Arduino? on: July 21, 2014, 07:09:59 pm
Reliable and rugged are to different things. arduino is very reliable within its specified operating conditions. Outside of its Safe Operating Area- all bets are off. What specific application did you have in mind?
5  Using Arduino / LEDs and Multiplexing / Re: Questions about 1w LED, 0.25w resistors, TIP120 on: July 15, 2014, 02:49:13 pm
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Question 1
the math looks about right. though actual numbers (Vf and R) may vary a little bit. i have bread boarded 1 watt Leds with a bunch 1/4watt resistors for a quick demo, but I certainly would never consider this route for any practical application. Use a constant current supply for optimal performance and reliability. they cost a dollar or two on ebay.
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Question 2
yea on paper looks like it might work but in real life those slight deviations in the actual values can significantly affect the circuit especially when you only have .6v across the resistor(s). And the voltage drop of the tip120 depends on the current flowing through it. Use a cc supply and a logic level FET.
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Question 3
Smoke will happen.  LED = diode. once it turns(@ 3.2v) it  offers practically no resistance and it will let as much current flow through it as the regulator will source burning  the LED up as well as the regulator. there are inefficient ways to use a vreg as cc supply, but just use a constant current  supply.
6  Using Arduino / General Electronics / Re: Slide Switch on: July 10, 2014, 07:23:48 pm
there are many ways to connect a switch. you need to be more specific and include some design parameters. Usually installation goes like: solder it and somehow affix it to the enclosure with hot glue, super glue, screws, duct tape or other.
7  Using Arduino / Motors, Mechanics, and Power / Re: Need help with RAMPS (reprap 3d printer shield for mega) on: July 10, 2014, 11:50:47 am
Yes the motor drivers must be plugged into the female headers on the ramps board and the motors are plugged into the male pin headers. unfortunately I don't think the easydrivers are directly pin compatible with the RAMPS board so will have to figure out how to make the necessary connections between the easydrivers and the RAMPS. or just buy the proper drivers mentioned in an early post.The Ramps board is not a controller or Motor driver per se- the Mega 2560, or sometimes Sanguinolo (sp?), is the controller (which you bought, right?), and the polulo A4988 chips are the drivers. the Ramps board is more or less just an interface board that makes the connections clean and easy.
8  Using Arduino / Motors, Mechanics, and Power / Re: Need help with RAMPS (reprap 3d printer shield for mega) on: July 09, 2014, 10:02:25 pm
Yes you can connect steppers directly to the RAMPS board. Did you by it as a kit for a 3d printer? If it is not part of a kit, you may also have buy the motor drivers.
9  Using Arduino / General Electronics / Re: LM2575 7.4V to 5V (i don't understand the circuit diagram) on: July 09, 2014, 06:15:36 pm
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great potential to destroy your phone, burn your house down, and die a fiery death
-a humorous over exaggeration, don't take life too seriously people. On the hand, if you have never seen what happens to an incorrectly charged lipo, you should definitely watch a few videos on YouTube before you try to make your own charging circuit.
10  Using Arduino / General Electronics / Re: Proper way of reattaching power cord in Ontario, Canada ? on: July 08, 2014, 04:18:06 pm
good link^
11  Using Arduino / Project Guidance / Re: Need help on solar charge controller on: July 08, 2014, 03:08:48 pm
Looks like you need at least 12 volts to turn it on according to the datasheet. Try a logic level FET instead "IRL". What type of battery are you charging? what voltage does it charge to? what voltage does your solar panel put out? what current are you charging the battery at? Schematic?
12  Using Arduino / General Electronics / Re: Proper way of reattaching power cord in Ontario, Canada ? on: July 08, 2014, 02:48:51 pm
Romex is generally used for in-wall wiring, conduit is also encouraged and sometimes required. But the wire nut thing seems weird to me, fairly common practice in California. Soldering is not at all commonly done in residential electrical installation. However, splices should be done in an enclosed junction or receptacle box.  Not sure if that's any help...
13  Using Arduino / General Electronics / Re: LM2575 7.4V to 5V (i don't understand the circuit diagram) on: July 08, 2014, 02:28:45 pm
There is a certain satisfaction that comes from DIY Projects especially in the face of all the nay-sayers; there is also great potential to destroy your phone, burn your house down, and die a fiery death.  Tread carefully. The benefit of building the circuit yourself is that you not limited to  a set form factor and you can add it to a PCB design. In this case, it probably would have been easier to go with a manufactured part.  Live and Learn.
14  Using Arduino / General Electronics / Re: LM2575 7.4V to 5V (i don't understand the circuit diagram) on: July 07, 2014, 01:13:24 pm
To better understand the intricacies of charging Apple products: https://learn.adafruit.com/minty-boost/icharging
To try to clarify-
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I was thinking about using a voltage divider for that.
Yes,  voltage dividers on the D+ and D-  are required for charging.
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Also, i tried connecting pin 2 to pin 4 with 10k potentiometer.
No, you must use the proper inductor if you want the chip to work as designed.

The LM2575 Is fairly easy to use as long as you use the right inductor (L1)- NOT a resistor. A Schottky diode is important as well (fast switching with high current), but selecting the right inductor is crucial to the stability of the circuit and accuracy of the voltage regulation. The datasheet for the LM2575 should include a fairly detailed explanation of exactly what part is required.  Read that datasheet! Power inductors aren't like simple resistors where any which one will do, and I would think it unlikely that you're friend would stock them, (unless of course he has built this circuit before.) The three main variables associated with selecting the inductor are the inductance, current capability, and resistance, the most important of which being the inductance value and current capability. The resistance corresponds to http://en.wikipedia.org/wiki/Q_factor of the inductor and determines how efficient and accurate the circuit is.
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Things are much more complicated than i expected
  Since it is a switching regulator, it is not as simple as say-a 7805.  But it doesn't need to be overly complicated as long as you pay attention to the important bits in the datasheet.
15  Using Arduino / Motors, Mechanics, and Power / Re: Need help making a charging circuit on: July 06, 2014, 03:13:09 pm
Yea a 12k will probably give you less than 100mah
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