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1  Using Arduino / General Electronics / Re: How to 'upgrade' motor drivers ? on: September 12, 2014, 10:35:44 am
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. Now I wanted to 'upgrade' it , so :
1- it would deliver more power to motors (better transistors) ;
2- it could work with higher currents ;
Higher power transistors are NOT going to automatically provide more power to the motors.  Transistors don't "provide" power, they switch/control power.

The power & current depend on the applied voltage, the characteristics of the motor, and the ability of the power supply to supply the power.    For example if you increase the voltage and/or use a bigger motor, the transistors might burn-up.   If that happens, you need higher-power transistors.    But, if the transistors don't get fried, bigger transistors aren't going to make any difference. 

With MOSFETs you'll typically get less voltage-drop across the drivers so you might get one more volt to the motors, and they will typically run cooler.  But, there are easier ways to get more voltage and if you need more voltage you probably want more than one additional volt.

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3- (I'm not sure if it's possible) I could connect it to an arduino UNO .
Probably, but I don't have the specs for the driver board.   Of course if you modify it, you'll change the specs. smiley-wink
2  Using Arduino / General Electronics / Re: Amateur Spectrum Analyzer on: September 12, 2014, 09:21:19 am
The Arduino is fast enough and the ADC has enough resolution for basic audio frequency analysis or a spectrum analyzer "effect", but I wouldn't try using it to build a "measurement instrument". 

There are two approaches - You can use FFT to do it in software, or there's the MSGEQ7 chip that filters the audio into 7 bands and sends a time-multiplexed varying DC signal to the Arduino.   Or, you could build your own analog filters if you want more frequency bands or better frequency resolution, etc.  If you search, you can find example projects.

For radio frequency use, I suppose you could use the Arduino as a controller for your spectrum analysis and to handle the user interface & display, etc., but the high frequency stuff would have to be done some other way.
3  Using Arduino / Audio / Re: Generating a 20khz sine wave on: September 11, 2014, 10:17:32 am
The PWM output will usually have subharmonics, but a square wave from a digital output will only have regular (higher frequency) harmonics which are not audible at 20kHz.     However, non-linearity in your piezo or speaker might create audible subharmonics or resonances.

If you want a true sine wave, you'll need a DAC or audio shield (which has a DAC), or you can filter a square wave, but to filter-out all (or nearly all) of the harmonics, you'd need an active filter.
4  Using Arduino / Project Guidance / Re: How do I make an inaudible sound transmitter? on: September 11, 2014, 10:02:26 am
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Inaudible implies something so quiet that you cannot hear it.
Inaudible just means you can't hear it.  It could be to quiet (or too distant), out of the audible frequency range, or a sound can be inaudible if it's masked (drowned-out) by a louder sound.
5  Using Arduino / Audio / Re: Audio amp dummy load with water heater element on: September 10, 2014, 03:49:23 pm
Digi-Key has 50W 8-Ohm resistors for about $4 USD.      Four of those in series/parallel would be good for 200W.   (It's always a good idea to derate resistors, and for 100W continuous I'd want 200W resistors.).

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So anyway... I was thinking about water heater elements. A 2000W 120V heating element works out to 7.2 ohms and is $10. I'd suspend it in a can of oil, I think. But I have no idea if they have a positive temperature coefficient or if there is enough inductive impedance to make a difference.
Since you'd be running it at less than 1/10th of it's nominal power, it shouldn't get hot enough to worry about the temperature coefficient and you shouldn't need an oil bath.    However, it might have enough temperature coefficient to measure differently (maybe lower) when cold or with "only" 100W or heat.

I built a 200W 8-Ohm load resistor out of a handful of resistors once...   Probably 20 8-Ohm 10W resistors if there's a way to wire 20 8-Ohm resistors in series/parallel and end-up with 8-Ohms...   I don't remember the details...  I remember the resistors were  the white rectangular type...      I put it in a nice box with 5-Way binding posts, and I think I still have it somewhere.

6  Using Arduino / General Electronics / Re: 110 V ac powering arduino on: September 10, 2014, 03:14:29 pm
You can build a simple unregulated power supply with a transformer, a full-wave rectifier, and a capacitor.  (Note that AC voltage has a peak about 1.4 times the RMS value, so a 6V transformer will work.)   The Arduino has a 5V voltage regulator on the board, so you don't need a regulated supply.

Take a look at this page.  The 3rd circuit (the one with 4 diodes) is the one I usually build.   You can buy the 4 diodes pre-wired in one package as a full-wave bridge rectifier.

Or, you can look for a switching power supply module.  (It's usually not economical or practical to build a switching power supply yourself.)

AC transformers tend to be bulky, and you might find a smaller switching supply module.    Switching supplies can take-up space too, and they do have transformers but the transformers work at higher frequencies so they can be smaller.

And if you ever want to build a regulated power supply you can add a regulator chip and a couple of capacitors.     I've built quite a few power supplies using LM7805 (and similar) voltage regulators.
7  Using Arduino / Project Guidance / Re: Zero Crossing Detector as high voltage power detector? on: September 10, 2014, 02:53:56 pm
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There are solutions like cheap 5V wall warts, relays, neon glow lamp...
But from my point of view the power waste is to big.
You can detect voltage with very low power consumption, but you still need some power to drive your circuit and/or to drive an LED.   For example, a digital multimeter might have in input impedance of 10-100 megohms, but it's powered by a battery.

How much power does one of those little neon lamps require?    It can't very significant. 
8  Using Arduino / Project Guidance / Re: random generator on: September 10, 2014, 12:26:04 pm
Code:
  randNumber = random(10);
That will generate 10 different values between zero and 9.  So far, so good.

Code:
if (randNumber <= 7) {
This will return true for values between zero and 7.   That's 8 of the 10 cases, with only 8 & 9 returning false.   
9  Using Arduino / Project Guidance / Re: Which arduino for my project with 100's of led's and sound? on: September 10, 2014, 12:04:18 pm
With shift registers you can have individual on/off control as many LEDs as you want using 3 Arduino output pins.

For 5 + 7 switches you'll need 12 inputs.

The Arduino Uno has 14 I/O pins, plus 7 analog inputs that be optionally programmed for digital input.   Two I/O pins are used for the serial/USB port, and it's easier if you avoid using those for anything else and use the "analog" inputs instead.

Note that the shift register method won't allow dimming or the use of RGB (multi-color) LEDs, and the standard shift register only works with "regular" LEDs, not "high power" LEDs.   "high


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I also found that the arduino due can play .wav files from an SD card.
For good quality sound, you'll want an audio shield (add-on board).    The Arduino doesn't have a true DAC, so although with PWM it can make some sounds.    The audio shield is also going to require some I/O pins, but I've never used one so you'll have to check the particular board you choose.

10  Using Arduino / General Electronics / Re: Troubleshooting Suggestions on: September 09, 2014, 03:50:35 pm
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IAnd what would this imply as to why I am getting the momentary continuity without the capacitor?  Or would it suggest that the momentary short is not really a problem?
It's NOT a problem.  That's the way capacitors work...  In series, they tend to "pass" AC and changing voltages and they "block" DC.    A "sudden" connection of the Ohmmeter is a "change" and current flows as the capacitor charges-up.    If you look-up the formula for inductive reactance (impedance) you'll find it's inversely proportional to frequency.

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I had tried this in the breadboard stage.  What I found was without the caps, it worked fine; when I added them, thigs started generally behaving very strangely.
Connecting small capacitors between power & ground should never cause a problem...  Maybe something was connected wrong or something was shorted?

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So I took the "Don't fix it if it ain't broke" approach.
That philosophy is OK to a point, and if your circuit is working you may not need them..    But, the lack of bypass capacitors can often cause random/strange/unpredictable problems.   If you go "into production" (or if you just build a 2nd identical circuit) you might find that only half of your boards work, or that 90% of them work, or that 90% of them fail, etc.

...If you remove half of the bypass capacitors on your computer's mother board, it will probably still work fine.   But its proper engineering practice to put a bypass capacitor on every chip...  Or on every power pin if you have a high density chip with multiple power-pins.   

P.S.
It's normal to get an "inrush" of current when you first switch-on a power supply or first connect a circuit with capacitors.    It's possible to do something "bad" like connect one of those 1 Farad (1 million microfarad) capacitors that they use with high-power car stereos to a small power supply.    In that case you might get too much current for too long and damage the power supply.
11  Using Arduino / Project Guidance / Re: Is it possible to build a complete home appliance with Arduino? on: September 09, 2014, 11:30:40 am
There is information on the Arduino Playground Page about interfacing with motors & high power devices.

With any project, you'll need to break it into parts.   With the Arduino (or any microprocessor/microcontroller project) you can start by separating the the project into 3 main parts - The input & user interface, the software (firmware), and the output & power control.

On the output side, it's often best to start by turning on & off LEDs before actually connecting motors & relays.   

And, you can usually do lots of output & hardware testing under software control (with little or no user interface). 

AC POWER ISOLATION - If you are running motors & heaters from AC line voltage, you MUST electrically isolate the Arduino (and yourself) from the dangerous voltages.   This can be done with relays, or optical isolators (or a solid state relay, which is electrically isolated).     The details of what's best to use depend a couple of factors, including what you are trying to control and what kind of control you need, but for now just keep in mind that there must be no direct electrical connection between the Arduino and the AC power.

MOTORS - Most applications will use a "regular"  AC or DC motor.   These are fairly easy to control with a relay, transistor, or MOSFET.    They tend to run fast and are often geared-down.  DC motors are easy to reverse (by reversing the direction of current flow).  To some extent you can control the speed, and the Arduino's built-in PWM capability makes DC motor speed control easy.    But, if you need precise speed control or if the load varies and you need constant speed, then you need some sort of speed-feedback and that gets trickier.     

With "regular AC or DC motors, or stepper motors, a micro-switch or an Opto-Interrupter is often used to set the end-points or "home" position.     i.e. A garage door opener doesn't need precise control, but it needs to know when the door is fully-open or fully-closed.

A stepper motor generally has 200 steps per revolution (1.8 degrees per step).  They require a special driver circuit, and you have to feed it a pulse every time you want it to "step".   (Actually, they can be "micro-stepped" to get a fraction of a step.)  They can run fairly fast, but not as fast as a DC motor, and most stepper motor applications run fairly slowly.   Of course, gears or pulleys can be used for more-precise control.   The print head in a printer is usually positioned with a stepper motor.    There is usually  a home sensor, but there is no other feedback.   So if the motor is stalled, or mechanically moved, or something unexpected happens where one or more steps are "missed", the software won't know the true motor position (until it's returned "home").

A servo motor is an angular motor that makes less than a full revolution.    They come with a built-in driver circuit, so you only have to supply power and an a pulse that sets the angle.     They are in a constant feedback loop.  So for example, if you are sending it a 90 degree control pulse and something mechanically slows-down the motor or forces it away from the 90 degree position, it will try to get back to that 90 degree target-setting.   Servo motors are geared, so they are not as quick as regular AC or DC motors.  Since they don't "spin" 360 degrees, the speed is usually specified as degrees-per-second under some stated load.

 
12  Using Arduino / Project Guidance / Re: amp after photoresistor on theramin project? on: September 08, 2014, 03:13:03 pm
You might just try a single transistor like this.   Leave the capacitor in series with the speaker and of course, the speaker & capacitor go where the solenoid & diode are shown on the schematic.

I'm not sure if that will make any difference but you don't don't have a true analog signal, you haven't built linear amplifier, and you don't need the "push-pull" circuit.    (I haven't done enough thinking/analysis to tell you if the 2nd transistor is hurting, but I do know it's not helping.)

One advantage to a linear amplifier (i,.e. the LM386)  is that you can put a volume control pot in front of it.
13  Using Arduino / General Electronics / Re: Lamp- smooth dimmer on: September 08, 2014, 01:17:25 pm
Take a look at the Examples.  There is an example for reading a potentiometer, and another example for fading an LED.  (You can modify the Fade-LED example to use the pin-13 LED that's already mounted on the Arduino board.)

You should be able to combine those two examples so that the pot adjusts the LED brightness.    Then, you can modify it for two pots and two LEDs.

Once your firmware & pots are working, there are examples for controlling a higher-current device with a MOSFET. 

If you are running off a regular flashlight/torch battery, that should be all you need because the batteries should properly limit the LED current.   If you are using higher-current batteries, you'll probably need a dimmable constant-current power supply that's designed specifically for driving high-power LEDs. 

NOTE: If you end-up needing a special constant-current LED power supply and you plan on using the pots to control brightness (with no automatic-program control), you can use the pots directly with the dimmable power supply and you don't need the Arduino.       
14  Using Arduino / General Electronics / Re: Will I blow everything up??? :) on: September 08, 2014, 12:55:16 pm
That looks safe as long as that "output" connection is not an Arudino output pin, and as long as there's nothing greater than 5V (or less than 0V) at that "output" terminal (when not switched to the 12V position).     The normally-open and normally-closed contacts of a SPDT switch or relay are never connected together, so as you've shown it, 12V will never be connected to the Arduino's input.

But, there is something screwy looking about your schematic...  It might be OK, but what's connected to "output"?      An output from "something" going into an Arduino input is fine (as long as you are in the 0-5V range).    But with the relay in the other position, it's unusual to connect the output from something to  to 12V.    For example, you should never connect an Arduino output to 5V or any other power supply, or to ground, or to another output.

Also, you probably don't need the pull-up resistor on the Arduino input.   There are pull-ups built-into the Arduino that you can optionally enable.

15  Using Arduino / Project Guidance / Re: Converting an organ to midi on: September 08, 2014, 12:33:50 pm
smiley-sad I don't think that's practical...   

Before you dive-into a project like this, I'd suggest you start by making a simple little "experimental" MIDI keyboard with a few push-buttons for keys.   You can start with just a few buttons/notes, or maybe 12 buttons for one octave.    For development  of the MIDI side of things, you can generate MIDI messages in software so you don't actually need buttons or a keyboard.

You might be able to "tap into" the key-switches and basically build a MIDI keyboard from there, but I don't think it would be worth the effort, and if the organ is worth preserving you probably don't want to make those kinds of modifications.   You can buy a simple MIDI keyboard for a couple-hundred dollars, and it's probably better than what you'd end-up with by "hacking up" your organ.

Or if you don't care about preserving the organ, I suppose you could build a MIDI keyboard from the parts.   But it's going to take you several months and who knows how it's going to turn out...  It depends on what you're after...   If you want to have fun with electronics it might be worthwhile.  But as a musician, it's probably not worth the effort (or the cost). 

There are a few computer applications that can convert audio signal to MIDI, but as far as I know they don't work very well with chords or multiple instruments.    Try searching for "WAV to MIDI", or "Audio to MIDI".    If you can find an application that works reliably polyphonically, in real-time,  you can run it on your computer and you won't need an Arduino.   (Converting one note at a time from audio to MIDI could be done with the Arduino.) 
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