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1  Using Arduino / General Electronics / Re: XLR cables on: Today at 01:13:57 pm
Tyipcally these cables are used for audio signals of microwatts or milliwatts (and micro & milliamps) so nobody cares about the current rating.    If you find the wire gauge spec for a cable that might be your best guide.   Some manufactures/vendors will specify the gauge and others will not.

Or, you might need to build our own so you can use a large wire and you'll know the gauge.

Monoprice has 16AWG XLR cables.   That should be hefty enough for 10A as long as your cable run isn't too long.
2  Using Arduino / General Electronics / Re: External VI and USB-Power on: September 22, 2014, 01:28:47 pm
I know that this is off-topic but how does a 10k resistor connected in series in the telemetry wire protect the arduino? As far as I know a risistor connected in series only drops the voltage.
The Arduino has internal protection diodes between the input an VCC and between the input and ground.    If the voltage exceeds Vcc or goes negative, one of the diodes begins to conduct and this "clamps" or "clips"  the voltage.     

That only works if the current is limited, and that's why you need the 10K resistor.   For example, if you connect a 12V power supply directly to one of the inputs, the protection diode will get fried, and other stuff inside the chip might be fried too.  It also only works if the Arduino is connected to power & ground.

The 2nd schematic on this page is the same concept.

The Arduino's inputs are very high impedance (megohms) so the "voltage divider effect" is limited and you don't get much voltage drop across the 10K resistor.    However, at high speeds/frequencies  the input capacitance could affect the signal (the resistor & capacitance form a low-pass filter) and with the 10K "source" impedance the input is more prone to noise pickup.

The 10K value seems perfectly reasonable to me, but I haven't checked the specs or done the calculations on the current capability of the protection diodes.     
3  Using Arduino / General Electronics / Re: Need Suggestions for Extending Approximately 40 Wires within 1 larger Wire on: September 19, 2014, 05:15:32 pm
My project is a replication of Guy Manuel's Daftpunk helmet.
I don't know what that is, and I can't research it right now...

What you are looking for is called "multiconductor cable".    Telephone & communications companies use lots of it.  But I agree with what's been said.   Connectors are bulky and wiring/soldering 40 conductors on each end of the cable is a pain if you can't use IDC ribbon connectors.

Maybe there is another way to do it?   Whatever "it" is. smiley-wink   For example, you can send data serially...  The whole internet is done serially.    I built a lighting effect with 48 individually addressable LEDs, and it's controlled serially with 3 Arduino outputs.     Of course, I have to also supply power and then there are some chips on LED side...   And it still required LOTs of soldering (two wires to each LED).
4  Using Arduino / Audio / Re: MP3 Modules and Speakers on: September 19, 2014, 11:16:51 am
1. What is a module (i.e. the one here: and how do i connect it to an Arduino?
It's not that clear to me either....  I can see how you communicate serially via the RX & TX pins, but I don't see how it connects to the SD card.

If yo look at the specifications, the commands in the table are in hex (hexadecimal =base 16).   For example, if you send E8 (232 decimal) over the serial connection, that's a "Volume Up" command.   You can use hex directly in your sketch, but if you want to convert between decimal and hex, the calculator that comes with Windows can do it in the "Programming" mode.

There is a serial library for the Arduino for sending/receiving serial data.  You just need two I/O pins.   Note that the TX and RX connections are criss-crossed.   The Arduino's TX (transmit) pin connects to the other device's RX (receive) pin and vice-versa.    i.e.  You don't talk into another person's mouth, you talk into their ear, and they talk into your ear. smiley-wink 

3. Does anyone know of a tutorial that shows how to build a mp3 shield from a VS1053  such as the one here (
That's usually not practical or economical...   Start with VS1053 datasheet.    You'd need to have a PCB made and the ability to solder fine-pitch surface mount components...  It's not something I can do "at home".   

And I haven't looked into what's available, but for a complex chip like this, you'd usually need to buy an evaluation board and probably obtain a software development kit (from the chip manufacturer) in order to do your hardware & software design & development. 

2. How do I use an 8 ohm speaker (resistors, connections, circuit, and  most importantly amplification)?]
You need an amplifier to boost the power.   Look for a "power amplifier" chip if you want to build one yourself.  For example the LM386 is a popular choice as a low-power amplifier.    The manufacturer's datasheet will give you the design schematic, showing any additional parts you need to add, etc..
5  Using Arduino / General Electronics / Re: Lesson Learned on Vishay VO14624 Solid State Relay on: September 17, 2014, 03:42:55 pm
Most "solid state relays" have a current limiting resistor, and the specs show a control voltage range.   But I've seen parts like that one too.   (Actually, I've seen the datasheets, not the actual parts.)     Personally, I'd call it a "high power optoisolator" if it doesn't have a resistor...  But the manufacturer gets to name the part! smiley-wink

Usually the clue is a voltage or current spec...  If it says it's controlled by 5-15V, or something like that, it has an internal  resistor.  If they specify a current, you'll need to add the resistor.
Usually the control voltage and output voltage & current ratings are specified "up-front", on the datasheet since they are very important in selecting the right relay.   If there's no resistor, the control current may be "buried" somewhere on a chart, since it's not quite as important in the selection process...   Generally, you can select the resistor later.   

So I just made a small tuition payment in the school of experience.
smiley-grin    I like that!   I'm going to try to remember that one! smiley-grin
6  Using Arduino / General Electronics / Re: How to 'upgrade' motor drivers ? on: September 12, 2014, 10:35:44 am
. 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.

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
7  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.
8  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.
9  Using Arduino / Project Guidance / Re: How do I make an inaudible sound transmitter? on: September 11, 2014, 10:02:26 am
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.
10  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.).

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.

11  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.
12  Using Arduino / Project Guidance / Re: Zero Crossing Detector as high voltage power detector? on: September 10, 2014, 02:53:56 pm
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. 
13  Using Arduino / Project Guidance / Re: random generator on: September 10, 2014, 12:26:04 pm
  randNumber = random(10);
That will generate 10 different values between zero and 9.  So far, so good.

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.   
14  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

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.

15  Using Arduino / General Electronics / Re: Troubleshooting Suggestions on: September 09, 2014, 03:50:35 pm
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.

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?

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.   

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.
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