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571  Using Arduino / General Electronics / Re: How do you calculate what the voltage will be after a resistor? on: February 04, 2013, 07:48:03 pm
So that would mean that if I have a 100mA load I'm going to get a totally different voltage than I would I I have a 4A load. That's not what I've experienced in practice. The voltage generally remains the same unless something with a massive amp draw is running.
There is something wrong with your measurement....   The ONLY way to get 40 times the current across the same resistance is with 40 times the voltage!   (With a 30-foot wire, you might not be able to measure that accurately.)   Ohm's Law describes the relationship between voltage, current, and resistance.   It's a law of nature* and it's always true.   i.e. If you double the current through a constant resistance, you double the voltage across the resistor.

The units of measure (Volts, Ohms, and Amps) are man-made, but the relationships are determined by God!  (Or nature if you like.)
572  Using Arduino / General Electronics / Re: How do you calculate what the voltage will be after a resistor? on: February 04, 2013, 07:34:46 pm
if the resistance of the wire is known, what formula will tell me the resultant voltage?
With a voltage divider, the voltage is divided in proportion to the resistance.   

Or, since the current is the same in both resistors, you can calculate the current from the total resistance and total voltage, and then knowing the current through each resistor, you can calculate the voltage across each resistor.

If you connect a voltmeter to your circuit, the resistance of the voltmeter becomes the 2nd series resistor.   The circuit is completed and a tiny amount of current flows.  (The current is small because the resistance of the meter is high).

nope. The voltage varies depending on resistance.
Are you measuring a voltage drop with a voltmeter/multimeter?    There is no voltage drop until you connect your meter, (or until you connect something to complete the circuit).  because there is no current flow unitl you connect your meter.    And, you will only measure a voltage drop if the resistance is very high.

Another example is that same battery and a 30ft wire. the voltage measured at the end of that 30ft wire will not be 12v because of the resistance of the wire.
Again, only if there is current.    And in this case, your meter cannot measure the voltage drop, because the resistance is so low compared to the meter resistance.
573  Using Arduino / General Electronics / Re: voltages questions on: February 04, 2013, 02:19:57 pm
there is just VCC , VDD, VPWR etc... that's why i was asking for the difference
Those are just names, and they need to be defined/documented somewhere.    Sometimes "knowing" that Vcc is usually +5V, might not be enough, or using the name/label '+5V' might not be enough, because there may be more than one 5V supply and you need to know which 5V supply is connected to which IC.  (i.e., you might have Vcc1 & Vcc2, etc.)

It's like anything else on a schematic...  It helps relate the schematic to the physical circuit.

Typically with an emulator/simulator, you can assign connections/meanings of your choice to these names/symbols.
574  Using Arduino / General Electronics / Re: anyone use these super strong LEDs? on: January 31, 2013, 01:25:38 pm
That same eBay seller offers this 10W LED-driver power supply.

To expand a bit on the voltage & current issue...   LEDs (all diodes actually) are non-linear.    A voltage change of 1/10th of a volt might change the current flow by a factor of 2.    On top of that, the forward voltage drop (at a constant current) varies with temperature, and from part-to-part.   So the proper solution is to use "constant current" power supply.    A constant-current power supply tries to supply the same current no matter what load is attached.  (At some point if the load resistance is high-enough, the power supply cannot supply enough voltage, and the current will be lower.  But, within it's normal operating conditions, the current is (approximately) constant.) 

With "normal" low-power LEDs, a constant-voltage power supply and a current limiting resistor can approximate a constant-current source, and thats how it's done with "regular" LEDs.  The higher the supply voltage, and the higher the voltage-drop across the resistor, the better it approximates a constant-current source.   But, the resistor usually wastes more power than the LED is consuming, so a current limiting resistor is not efficient and not practical for higher-power LEDs.   A constant-cuirrent switching supply (which uses an inductor) can be nearly 100% efficient.  Just about anythhng you buy that has 1W or higher LEDs is going to have a constant-current switching supply.    The downside to a constant-current (switching) supply is complexity and cost.

A "normal" power supply is constant voltage...  A good well-regulated 12 power supply will supply a (approximately) constant 12V as long as the input voltage and current-load are within spec.    Actually, most "things" are constant voltage...  For example the Arduino's output pins are (about) 5V (when  "on" ), as long as you don't exceed the 40mA output-current rating.
575  Using Arduino / General Electronics / Re: Small power source for one century on: January 30, 2013, 09:09:38 pm
...a mechanical watch mechanism might be a better bet for the timing - if you can find a power source with sufficient shelf life to wait to be activated.
That's probably the most "practical" idea!    I THINK I've heard of mechanical clocks that only have to be wound once a year.    One hundred of these mechanisims with one triggering another in series could probably work.    And, for the "final action", probably a bigger spring-driven generator.   

You'd have to make sure there's no corrosion and that the lubrication won't dry-out.   

There are ways of generating electrcity with thermal differences, etc.   But you still need to STORE the energy in a battery (or capacitor) to continuously supply the clock.  It's the long-term reliability of the battery (with its nasty corrosive chemistry) that I'm worried about.

576  Using Arduino / Project Guidance / Re: Working With ICs That Are Too Small For Legs To Fit Into Breadboard on: January 30, 2013, 08:39:06 pm
Here's one example.   With most (all?) of these things you'll need to solder the chip to the adapter board. 
577  Using Arduino / Project Guidance / Re: Help! AMBX RGB LED light extension project! on: January 30, 2013, 03:10:23 pm
These test points (TE4, TE6 and TE7) would be much easier to solder onto, but could they be connected to Arduino safely (within current limit?) and would it be easier to decrease this voltage to the 5v for monitoring instead of using the IC1's LED-level output?
In any case, you will need to reduce the voltage*.   Your circuit has signals between zero and around 18V.   The Arduino can be damaged with voltages above 5V.   Reading voltage pluses with a meter only gives you a rough idea of what's going on, and different meters will "average" differently... 

Looking at the schematic, I don't think those test points are going to give you a good signal (i.e. it doesn't like it will go close enough to 0V).

The outputs of U1 (pins 1, 7, 8 ) are probably the best place to pick-up the PCM signal (which will switch  between around 0 and 18V).   A voltage divider (2 resistors) can be used to knock-down the voltage.     I'd use 10K as the aproximate total resistance for your voltage divider.    2.7K and 7.5K are standard values that will probably work.

Then, if you are going to use an Arduino analog input, you'll need a low-pass RC filter to convert the PWM to variable DC.   I assume a time-constant of around 0.1 Second should work.   And, again, I'd start with about a 10K resistor and you can calculate the capacitor value.  (The resistors in the voltage divider will interact with the filter to an extent, but you'll probably be experimenting with different values anyway.)

I have to agree that the Arduino is probably overkill!   But, it does give you the ability to do anything you want with those 3 color-signals!

* On the Arduion's inputs, we have to be concerned with voltage.   On the outputs, we have to be concerned with current.   The relationship between current, voltage, and resistance (or impedance) are is described by Ohm's Law.  The very-high input impedance of the Arduino (under normal conditions) means that current flow into it is very-very low.
578  Using Arduino / Project Guidance / Re: Random Flashing Strobe Control on: January 29, 2013, 05:49:25 pm
I will also need to bias my random outputs so that I do not repeat the same strobe twice in a row.
Probably the easiest solution is to put your random-variable selection in a loop (probably a while() loop) and loop 'till the random next lamp is different from the current lamp.

i.e. Pick a random NextLamp number and if NextLamp == CurrentLamp, continue looping and get another random Next Lamp.   If they are not equal (which will be true most of the time), break out of the loop.   As long as this loop is running fast enough (relative to your flash interval), you can randomly pick the same number several times in a row and you'd never see a problem.

Of course when the time is up, CurrentLamp will be assigned the value of NextLamp and you'll have to find a new-random NextLamp.

Another way to do it is to make an array which excludes the CurrentLamp, and then pick a random element from the array.   (Something like this is often done to simulate a deck of cards, where you can't select the same card again after it's removed from the deck.)
579  Using Arduino / Project Guidance / Re: Random Flashing Strobe Control on: January 29, 2013, 05:07:28 pm
I think I will need to use some sort of psuedo mutitasking or timer variables?
By using the Blink Without Delay technique, you can have multiple delays that don't interfere with each other.

Or, they can relate to each other...  But in any case, you can have more than one timer running at the same time, since your loop runs continuously without any delays in the actual loop.

So you can trigger the 1st strobe

... Then after some delay, send a trigger to the 2nd strobe before the 1st one actually fires.

... Then, after enough time has passed for the 1st on to fire, turn it off before it can fire again.
580  Using Arduino / Project Guidance / Re: Lower the voltage comming into the Arduino Pins? on: January 28, 2013, 06:59:20 pm
First, since 90V can kill your Arduino  I'd recommend a pair of protection diodes* and a series resistor.   (This circuit will knock-down the voltage in a non-linear fasion, so it's just protection against over-voltage...  It is not used to attenuate a 0-90V signal down to 0-5V inearly...   i.e. 90V or 45V would both read "5V".)

Then, you'll need to measure the voltage output under your real-world conditions.    You can experiment with a parallel resistor (probably in the in the megohm range) to knock-down the signal (linearly), if necessary.    You are unlikely to get 90V and you might end-up getting less than 5V depending on your pressure & physical configuration.   (But, I'd still recommend the protection diodes.)   

Or, you can use a regular 'ol voltage divider (again along with the protection diodes).   But, with the high source impedance of piezo will create a 3-way voltage divider, and your signal will be reduced by more than the calculated amount...    A lot more if you use low-value resistors in the voltage divider.

i need a voltage sensor because i want to detect the voltage comming from the piezo from different pressures. so i want the exact number...
That's only gong to work for quick pressure CHANGES.   A constant pressure (with no physical movement) is NOT going to generate a constant voltage.**   I believe the piezo acts like a small capacitor, so it might sort-of hold the voltage for a several microseconds as it discharges through the load resistance.

* The Arduino has built-in protection diodes, but they are rated for low current and are only there as a "last resort" in case something unexpected happens (such as static discharge).   If you are experimenting with something that puts-out more than 5V in normal operation, you should take steps to reduce the voltage before it hits your Arduino.

** Conservation of energy...   Gravity can generate electricity as water flows down and through a generator.  But, you cannot use the static pressure of water behind a dam to generate electricity.

581  Using Arduino / General Electronics / Re: basic question... on: January 28, 2013, 03:11:49 pm
Are the lamps themselves marked 220V?  Many halogen lamps are 12V and there is a step-down transformer built-into the fixture.

I am buying 110v lamps but I am not sure if I can buy 50w (easily found around here) lamps or if I should stay with 35w.
Wattage is directly related to heat.   The maximum wattage rating should be marked on the fixture somewhere.  Or, check to see if there is some rating on each of the 5 sockets.   If each socket is rated 50W or more, you can probably get away with it.    But, if there is any plastic, the additional heat may melt it.    If you exceed the rating, and your house burns down, you can't sue the lamp manufacturer...  But, your insurance should still cover the damage... smiley-grin

Note that if you keep the power the same (35W) at a reduced voltage, the current will increase.*   You are probably safe, but if you can se the wires, they may be marked with the current rating which should have plenty of safety margin since the whole thing will only pull a couple of amps and most lamp wiring will be rated for more than that.  (Watts/Volts = Amps).   

Second question.. I tried to turn on a single 220v lamp and it worked weakly as expected, but when I put all the five lamps one of the wires bursted. Why? I thought it work weakly as it did with a single lamp.
  That should not have happened in any case.  Maybe the bulb was defective (shorted-out).    A 220V lamp connected to 110V is something like using a dimmer, plus the fixture should be designed to survive a 110V brown-out when connected to 220V.    Something "funny" could happen if there is a switching step-down power supply, but nothing that bad[/b] should happen.

* The current will increase if you use 110V/35W bulbs.    With the original 220V bulbs, reducing the voltage also reduces the current.
582  Using Arduino / Installation & Troubleshooting / Re: 9V in 5V arduino OUTPUT!!! on: January 24, 2013, 07:29:53 pm
If you have a ladder rated for 500 pounds, it might not collapse with 900 pounds on it...   But, it's always safe at 500 pounds.

Where I work, we make a board that runs off of 5V.   There is about 20 chips on it, all rated for 5V.   A few times I've accidently connected 12V to the power input.   Usually the RAM chip will fry, and sometimes the CPU will fry.   But the other chips usually survive.

Fortunately, I don’t have any experience with over-voltage on the Arduino! ... Yet.
583  Using Arduino / General Electronics / Re: Peltier / Thermo Electric. on: January 24, 2013, 06:31:05 pm
You can extract energy from a system whenever there is a temperature difference (as the heat moves from the hot-side to the cool-side).   So, you could extract energy from the difference between air and water temperature during the day when the air is hotter than the sea, and again at night when the air is cooler than the sea.

I'm sure if this was economically efficient, it would be done.    Energy efficiency is not a factor, since there is plenty of sea & air and an inefficient system just has to be larger.  It's the same issue with photovoltaics...  There is plenty of sunshine and the energy is "free".   But in the real world, the electricity from photovoltaics is more expensive than traditional sources.

But of course, the environmentalists won't like you if you start transferring heat between the sea and the air! smiley-grin
584  Using Arduino / General Electronics / Re: Inverting buck boost converter load connection on: January 24, 2013, 02:51:54 pm
Yes, if you want to reverse a DC moter, you can simlply reverse the connections.

With relays or a bridge circuit, you can make a motor driven from a single-supply that runs either directions.

Sometimes you need a true negative voltage (referenced to ground).   For example, audio signals are AC (the voltage swings both positive and negative) so it's often handy to run an audio op-amp from + & - power supplies (although you can make an audio amp or preamp with a single supply).

Or sometimes if you are working with very-low positive DC voltages, it's easier to build a circuit that goes below zero volts, and that allows you to go down to zero-volts linearly.

If you are building a power supply (that runs off AC house power) you can make it put-out both positive & negative voltages (i.e. use a center-tapped transformer) and you don't need a separate inverter circuit.
585  Using Arduino / General Electronics / Re: Very basic resistor/piezo question on: January 24, 2013, 02:25:50 pm
With the resistor in parallel, you are creating a voltage divider where one of the "resistors" is the internal resistance of the piezo device.   Yes, that will reduce the voltage.   Since the piezo (unlike most voltage sources) has high source-impedance, a high-value resistor in parallel will reduce the voltage.

A resistor in series with the Arduino input will also create a 3-way voltage divider where the voltage is divided between the piezo, the resistor, and the Arduino.  However, since the Arduino has an input impedance of around 100M, almost all of the voltage will be "dropped" across the Arduino input, and the series resistor will have little effect.

Normally, you'd use two resistors to make a regular voltage divider and you could calculate the voltage drop.  With the piezo as one of the "resistors", we don't know the internal impedance of the piezo, so we can't calculate the voltage drop.  (I believe it's capacitive, rather than resistive.)   But, if you want to experiment, a single parallel-resistor is fine.

BTW - You have an unknown and uncontrolled voltage which will go positive and negative.    I'm not sure what voltage you are getting, but the Arduino is limited to 0-5V.   Any negative signal, or any signal above 5V can damage the Arduino.   So, I recommend that you use a pair of protection diodes.
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