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16  Using Arduino / Project Guidance / Re: Guitar Pickup Winder on: April 03, 2014, 07:08:59 pm
You probably don't want a stepper motor for the winding motor.   You just need an optical or hall/magnetic sensor to count the revolutions.

I'm not sure you need the other stepper motor.  I don't think a winch normally has a guide... I think just the cable thickness &  tension make it wind-up nicely once you get it started.   Or, a bobbin on a sewing machine seems to wind-up neatly by itself without manually guiding it back-and-forth.    And, it might get really tricky to get it in-sync with the wire thickness.  Maybe you can experiment to see if you really need to guide the back-and-forth movement.  (Or, maybe you already know that you do need the 2nd motor.)

The tricky part will be measuring the resistance of the coil as it spins
That's not going to work.   Magnet wire is insulated with enamel.  You have to scrape the enamel off the ends to make contact and if you scrape it off in the middle of the winding it's going to short-out when you wind it.

However, wire of a known gauge does have a known resistance per foot (or per 1000 ft).    You can measure the amount of wire being used (with some kind of rotating pulley gizmo that you can "invent") and calculate the resistance.    If you know the resistance you want, you'll know how much wire to use.

A quick search turned-up a chart on Wikipedia that goes down to 40AWG and shows 1049 Ohms per 1000 feet (about 1 Ohm per foot).   Obviously, the resistance of 42AWG will be higher.

way to input the desired guitar pickup coil resistance, and LED display to show desired information (desired resistance, actual measured resistance, count the number of revolutions, plus a few others).
If you need to do lots of calculations with lots of variables, I'd consider either using a spreadsheet or interfacing it with a computer (so you can use the keyboard, screen, and calculating/programming capabilities of the computer).   Otherwise, it almost sounds like you are building a special-purpose calculator and you'll need a keypad and some function-buttons, and it could get complicated to build and complicated to use.

I'm always trying to keep thins simple, so I'd probably just want to punch-in the number of turns and have it stop automatically when it's done.

I don't know that much about guitar pickups, but I think the number of turns and inductance is probably more important than the DC resistance.      What's the typical resistance?   I'm betting the DC resistance is far-less than the 1 megohm or more input on a guitar amp.    As long as the source impedance (pickup) is low compared to the load impedance (amp input), the source impedance makes very little difference.   For example,  a change from 1k Ohm to 5K wouldn't make any difference (as long as the number of turns and inductance remain the same...  In the real world all of these things are going to change together).

If you don't know this already, impedance is a combination of resistance, inductive reactance, and  capacitive reactance.    You make an inductor by winding a coil (usually around a core) so a pickup is primarily inductive.   Inductive & capacitive reactance depends on the inductance/capacitance and frequency, so they can affect the "tone".     The input on the amp (or effects pedal, etc.) is primarily resistive, but the amp's input impedance interacts with the pickup's inductance to affect tone..
17  Using Arduino / Project Guidance / Re: Custom PC Watercooling and Fan control system. Fan control help? on: April 02, 2014, 02:58:10 pm
This is, in many ways, intended to be overly engineered just to ensure that my precious PC doesn't get damaged.
I've never seen a PC physically damaged from "normal" overheating.    If something literally burns-up, it's normally damaged before you get smoke & black-dead components.   

I haven't had a CPU overheat in a long time...  When it did happen (due to a "frozen" CPU fan) the CPU would slow-down to a crawl to protect itself and there was no permanent damage.      I believe Intel & AMD processors both have over-temperature protection built-in.
18  Using Arduino / Project Guidance / Re: Custom PC Watercooling and Fan control system. Fan control help? on: April 02, 2014, 02:49:00 pm
My current problem is knowing the best way to control the 7 and maybe more fans that I will be controlling. This fans are currently set in 5 groups or channels based on location and purpose in the case so. I want to be able to set them manually and also set them programmatically.
I question the need to control the fans independently...   i.e. It wouldn't make sense to have some fans running full-speed and others off.

So I was thinking that the best way to do that would be to have a slide pot for manual input
That would be OK.  But it's mechanically easier to drill a round hole and mount a rotary pot.   Another option would be to have buttons for "faster" and "slower".   And, with an LCD you have the option of "soft buttons" where a button can have one or more functions, controlled by software.

then have digital pots sending a signal to a mosfet to then be the control on the 12V line to drive the PC fans.
It's better to use PWM to a MOSFET.   You wouldn't need the digital pots and you already have PWM outputs.   Linearly controlling the voltage/speed with a pot (or digital pot) is inefficient and it requires the MOSFET to dissipate heat.

Also, I prefer to buy all my parts in basically one go. I know this probably is not the best practice, but with limited budget, shipping costs become a pain.
It's not "bad practice", and I usually like to buy a few extra parts in case something "goes wrong".   But realistically, you'll probably end-up placing at least one more order before the project is done.
19  Using Arduino / Audio / Re: Electret microphone without breakout board on: April 01, 2014, 04:18:30 pm
You can check the A/D converter and your software with a pot.  There is some information here.

Testing you mic & preamp circuit is a little trickier.    It's probably best to get a pre-built breakout board for testing purposes.  When you get everything working with the breakout board, you can try your own mic & preamp circuit if you want.

If you have a multimeter (which you probably should have) you can measure the DC output bias as well as the AC signal.    (You may not be able to measure the un-amplified AC signal from the mic, because it's only a few millivolts.)  You could also test your mic/preamp by plugging it into your stereo system or line-in on your computer's sound card...   But, I really don't recommend it because there is a small chance of damaging your stereo or soundcard if there's something wrong with the circuit.

I tried that, but all I got from trying any of those results was a random number repeated that did not change
What does that mean?   If it's repeated and doesn't change, I wouldn't call that "random".

When you read/sample audio the numbers normally "look" random because you are reading "random" places along the waveform.       The breakout board normally has it's output biased 2.5V.   With silence, you should get readings around 512.    As the sounds get louder, the numbers should "spread out" and you should get some bigger numbers and some smaller numbers with lots of "random" values in-between.    The average should remain around 512.

This isn't necessary if you just want to get the "loudness", but with "normal" digital audio the waveform is sampled at a constant-known rate (44,100 times per second for a CD).   The values look random, 'till you plot them at the same constant-rate.  Then you can "connect the dots" and re-create the waveform.    And in fact, real-world sound/audio is quite "random".   If you've ever seen a VU meter, the readings would look random if you are not listening to the sound.
20  Using Arduino / Audio / Re: Acceptable speaker impendance on: April 01, 2014, 01:32:58 pm
An Arduino output puts-out 5V (when on/high) at 40mA or less.

Using Ohm's Law we can calculate the minimum allowable resistance (for the maximum 40mA current):  5V/0.040A = 125 Ohms.

So that's a minimum resistor value of 109 Ohms.

Note that most of the energy will be wasted in the resistor so you may not get enough volume.

5V/16 Ohms = 313mA.    If you were to connect the 16 Ohm speaker directly, you'd probably get less than 5V out, so the current would be less than calculated but the Arduino might overheat and die!
21  Using Arduino / General Electronics / Re: 4 ohm speaker on 16 ohm system on: April 01, 2014, 01:21:33 pm
 smiley-razz Where in the heck did you find a 16 Ohm amplifier???

What's the application, and what's the wattage rating on the amp?

Could I just connect a 12 ohm resistor in series and deal with the reduced sound, or is there a better way?
1/4th of the voltage is 1/16th of the power and a 12dB loss.

Four 4-Ohm speakers in series (or two 8-Ohm speakers) might be a "better" solution depending on your design requirements.  (Or get a different amplifier. smiley-wink )

It will still work, just don't turn the volume so high.
There is a risk of "frying" the amp.   You can take the risk if a dead amp is not a big issue for you.
22  Using Arduino / Audio / Re: Best anti-aliasing filter to use for sampling audio on arduino? on: March 31, 2014, 04:57:21 pm
You are going to need an active filter.   In the old days, we'd use The Active Filter Cookbook.    But, I assume this stuff is online now.

Or, you can get a Switched Capacitor Filter IC.   That's probably the simplest solution.

Every filter is a compromise and the "type" of filter is up to you.     As you may know, the cutoff frequency is defined as the 3dB down point.    So, a 4.8kHz filter is NOT going to work.    You probably want any alias signals at least 40dB down.    That's the basic problem with a simple passive RC filter...   You'd have to set the cutoff frequency way below 4.8kHz in order to get significant attenuation at 4.8kHz.
23  Using Arduino / Audio / Re: Mix several sinewaves? on: March 31, 2014, 12:19:21 pm
Mix or add? The two mean different things, or at least they can. To be fair, we call an audio board a "mixing console"...
An analog mixer is built with a summing amplifier.   If you mix a vocal and a guitar, they are summed.   Digitally, we usually need to scale-down the samples before mixing because the sum may exceed the value we can hold with a fixed number of bits.
24  Using Arduino / General Electronics / Re: Relay socket or holder on: March 31, 2014, 12:09:58 pm
It looks like it will fit in a regular DIP socket, but I'm not sure if you can find an adapter board with screw terminals.

Oh and semi-related - I know to use a diode across the terminals when connecting these to a microconttroller, but any reason to use a diode (or not use) when connecting to something "dumb" like a light switch and cheap USB power supply?
You pretty-much always need the diode.    The high-voltage "kick back" can shorten the life of a mechanical switch (or relay contacts) and the effects on a power supply are unpredictable.
25  Using Arduino / Project Guidance / Re: 3 way switching 230v on: March 31, 2014, 11:58:09 am
Yes, you need a relay.   You need a single-pole double-throw (SPDT) relay.   DPDT relays are more common, and you can simply leave 3 terminals unconnected.   

This page shows you how to wire a 3-way switch.

There's one possible issue...   You may need some "feedback" so the Arduino "knows" if the light is on or off.     
26  Using Arduino / Project Guidance / Re: Recommend me a lighted magnifying lamp on: March 27, 2014, 03:23:17 pm
@Riva (or anyone else) how did you make the word "these" into a hyperlink?
smiley-wink That's tricky to show you, because when you do it right you don't see the formatting commands....    I'll add a space between the bracket and and 'url'...  That will mess it up just enough so you can see it:

[ url=][]Arduino Forum[/url].

Take out that extra space and it shows-up like this:   Arduino Forum.

(I normally also bold, underline, and color the link.)
27  Using Arduino / Project Guidance / Re: Recommend me a lighted magnifying lamp on: March 27, 2014, 03:11:13 pm
We have one similar to this on every workbench where I work.   You'll find these all over the place at any electronics company, and I've seen them on jewelers & watch repair workbenches.

We also have a couple with higher magnifying power, but with higher magnification you have to get the lens very close to your workpiece and that makes it difficult to use while soldering.  I also have a couple of hand-held magnifying glasses, and a jeweler's loupe.   (I'm over 50 years old, so I need reading glasses too!)

For home use, I first got one similar to the lamps we have at work, but a cheaper one with an incandescent lamp.    But, it gets very hot and sometimes you're working with your face right-up against the thing.    So, I got the "standard" fluorescent version.    You can also get them with LEDs.

We also have a digital microscope similar to this.    At another company, we had a Stereo Microscope which can be really nice for inspecting surface mount components.  (The "3D" depth perception you get with a stereo microscope makes a surprising difference compared with a regular "one-eye" microscope.)
28  Using Arduino / General Electronics / Re: Replacing potentiometers with digipots on a fuzz effect pedal on: March 27, 2014, 01:56:11 pm
What if I put two 250K digipots in series?
Then you'll have two center-taps with neither center-tap covering the whole range....   One 250K should be fine.
29  Using Arduino / Project Guidance / Re: Wristwatch with four buttons and Nokia 5110 on: March 26, 2014, 05:50:46 pm
You might be in a little too far over your head with this project.
I agree.   Miniaturizing stuff "at home" is REALLY difficult.  That goes for the mechanical assembly as well as the electronics.      I've worked in electronics for many years and I wouldn't try making a homemade watch.

At least, try building a clock before attempting a watch.

Have you ever looked inside a digital watch?  You might want to buy a cheap one just to take it apart and look.  Look at the circuit board and imagine soldering the parts on.
30  Using Arduino / Project Guidance / Re: New project suggestions, automating a motor to run one a day for a curtain time. on: March 26, 2014, 05:15:36 pm
This may seem easy but I have zero knowledge of anything technical so I'm very lost but believe this must be possible...
I'm not sure I'd recommend learning microcontrollers, electronics, and programming for a one-time project.    It would be a good starter-project if you want to learn this stuff.

Can you handle the mechanics and hooking-up a motor?    If you can do that, I'll recommend a few things to simplify the project -

The easiest sketch (Arduino program) is the Blink LED Example.   This is what people normally load & run to make sure the Arduino IDE software is running, everything is connected properly, the Arduino board is running, etc.

The example shows an external LED connected, but if you get a standard Arduino UNO, there is an LED mounted on the board and connected to pin 13.  So you can just plug the Arduino into your USB port and get everything set-up without any wiring.

Now, if you can live without a real-time clock (time-of-day clock) and you just need to run the motor for some period of time every 24 hours, you can simply modify the blink sketch for a LOT longer "blink" time, and the software is done!  

The delay() function needs to know the number of milliseconds.   One millisecond is 1/1000th of a second, and I'll let you calculate how many milliseconds there are in 24 hours.     And, you'll have to convert the motor run-time to milliseconds.

The timing won't be as accurate as a clock, but perhaps you can live with a little drift.

If you need to add a real-time clock (and display) that will complicate the electronics (hardware) and the programming (software).     But still not too hard, and still a good "starter project" if you want to play with this stuff for a few months.

The Arduno puts-out 5 Volts at 40mA (or less depending on the load resistance/impedance).  That's not enough to directly power a motor.   The simplest solution is to use a  relay.  A relay is an electrically controlled switch.   The relay coil (an electromagnet) connects to the Arduino.   The coil needs to be rated for exactly 5V, and 40mA or less.     The relay contacts are wired in place of a switch.   The relay contacts should be rated for the voltage and current of the motor or higher.    (Almost any relay will handle a small battery powered motor.)
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