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3496  Using Arduino / Motors, Mechanics, and Power / Re: feedback turns off heating element. on: December 24, 2013, 01:24:27 pm
Actual full details of the fans, power supply and heater element are needed to start
designing control circuitry for them.  It sounds like everything might be 12V at least
which simplifies things.  Is the heater 25A then?
3497  Using Arduino / Displays / Re: What distance can LCD be separated from Arduino? on: December 24, 2013, 01:21:15 pm
And how does that stop RFI and noise pickup exactly?
3498  Using Arduino / General Electronics / Re: Through Hole PCB - Traces? on: December 24, 2013, 01:17:00 pm
Sending it through a PCB is pointless.

Add some thick wire directly from the MOSFET to wherever it needs to go.

You forget that the gate drive signal isn't high current and can be routed on the PCB
even if the source/drain circuit can't be.  PCBs make everything neat and putting a wire
through a hole before soldering really reduces the risk of a dry solder joint as there
is proper mechanical support as the solder solidifies.  And lastly you can put print
or writing on the PCB to document it.
3499  Topics / Science and Measurement / Re: My arduino DAQ project on: December 24, 2013, 01:09:21 pm
Nice - what datarate do you get over BT?  You are not trying spectrum estimation
on the Arduino?
3500  Topics / Science and Measurement / Re: Aviation altimeter for microlights on: December 24, 2013, 01:05:48 pm
Love the "Caution: read manual before flight" sign.  I wonder if Apollo had that?!
3501  Products / Arduino Due / Re: SPI on an Arduino DUE on: December 24, 2013, 12:58:52 pm
No, its pinned out identically to every other Arduino so that shields only need one
version (however older shields don't understand IOREF and 3.3V at all).

Its actually good practice to generate 3.3V locally on each shield from 5V as the voltage
tolerances are tighter and you don't risk overloading the host Arduino's 3.3 supply,
and you don't inherit noise from the other boards in the stack (noise matters more at
lower supply voltages).
3502  Using Arduino / Programming Questions / Re: what wrong help please on: December 24, 2013, 12:52:29 pm
You must have case correct.  So the #include <DHT11.h> must match the
.h filename exactly (I presume its uppercase, they normally are).

Also the type is usually uppercase, the instance variable lowercase, so this looks
completely suspect:
dht11 DHT11;
would have expected
DHT11 dht11;
3503  Using Arduino / Programming Questions / Re: Why does variable revert to previous value? on: December 24, 2013, 12:44:30 pm
Firstly you didn't mention you were using the Due - this is important!

Anyway sizeof (char []) is the size of a pointer variable. Since you get a
value of 4 you must be on the Due.

I think you wanted to use strlen() to get the string length?

You cannot write to a string constant - that's not allowed (on the Due nothing
happens when you write, on the Uno it happens to overwrite the constant (basically
the behaviour is "undefined" so you can't expect it to do any particular thing.)

The reason one of the printlns seems to catch the new version of chars is simply
due to compiler optimizations.

So don't overwrite a string constant, use strlen() not sizeof().
3504  Using Arduino / General Electronics / Re: How can I drive this random speaker at max power, and various frequencies? on: December 24, 2013, 12:26:12 pm
Class D amplification is ideal, much more efficient, but for a subwoofer driver you might
be talking anything from 50W to 400W power (whether that's actually necessary is another
question)....  A signal generator is needed to generate nice sine wave of varying frequency.

In theory at least an Arduino could generate fast PWM in antiphase (a class D signal) which
then only needs boosting with a MOSFET H-bridge and filtering with LC filter to the speaker.

In practice its quite challenging to roll-your-own like this.
3505  Using Arduino / General Electronics / Re: Through Hole PCB - Traces? on: December 24, 2013, 12:16:38 pm
For really heavy current you use the PCB just as a convenient substrate to solder
both the component and its wire to, rather then push current through 35um thick
copper foil!   You can have the wire go through holes next to the component and bend
the strands over to meet the component's lead and solder them together.  The board
keeps leads apart and provides mechanical support only.

There are online trace-width calculators that can help you decide.  Remember heat
goes up as the square of current so a doubling of current is 4 times the temperature
rise.  10A is a lot different from 5A, for instance.
3506  Using Arduino / General Electronics / Re: op amp circuit don't work (Differential Amplifier) on: December 24, 2013, 12:12:05 pm
If you want a differential amp you must connect _both_ inputs to voltage sources (low
impedance).  The circuit output difference (opamp output - ground) is then equal to
the difference in input voltages.  But you must drive it from low impedance.

If you leave one input unconnected you have an entirely different circuit.

If you have a high impedance source you'd better use a non-inverting stage first,
this is the only opamp configuration with high input impedance..

Perhaps your circuit needs a mid-rail virtual ground?  Most opamp circuits do.
3507  Using Arduino / Project Guidance / Re: Speed Requirement for fast encoder and sensor ! on: December 24, 2013, 11:49:43 am
Why does the count handler loop over an array at all.

Interrupt routines should do the minimum work possible.  Looping over
26 elements of an array obviously isn't the minimum work possible, and this is slowing
down the handler a lot.

Normally counting a unidirectional encoder would be:
volatile long count ;

void handler ()
  count ++ ;
3508  Using Arduino / Project Guidance / Re: how to generate waveform on: December 24, 2013, 11:45:06 am
2.64V ??  How did that happen?  If the output isn't close to 5V peak-to-peak (for a
5V supply) you are overloading the pin.
3509  Using Arduino / Project Guidance / Re: Trying to build a frequency-sensitive LED milk crate wall in lieu of a drummer. on: December 24, 2013, 11:38:41 am
And this:  - if you
rework the LED array driver then the FFT part could be useful.

For this sort of music visualization FFTs and DCTs aren't great as they
split the spectrum up linearly - you really want to pick out each note or
octave which takes something a bit more sophisticated (probably beyond
an Arduino alone, laptop or RaspPi needed perhaps).

An Arduino could easily drive LED strips via an array of MOSFETs or Darlingtons,
and could for instance be controlled in real time via USB-serial connection.

Simple FFT or DCT can be done on the Uno / Mega, but don't expect 1024 point
resultion or a bandwidth beyond 5kHz...

The Due is more capable and can handle full range audio at 12 bit resolution,
and has a lot more pins for controlling LED channels, but is 3.3V and would
need careful interfacing (voltage too low for most MOSFETs, current low too, but
enough for Darlingtons)
3510  Using Arduino / Motors, Mechanics, and Power / Re: feedback turns off heating element. on: December 23, 2013, 10:02:04 pm
No microcontroller handles high current directly.  You use a switching device such
as BJT, MOSFET, relay, SSR, or opto-triac for that.  Depends on the voltages and currents involved.   If mains is involved then you need to understand how to control it safely.

You also need to choose a temperature probe - a thermocouple seems unnecessary
for just water, they are normally used for high temperature (upto 1000C), many
semiconductor temperature sensors are available that work in the range 0..100C.

A thermocouple would be more robust (say the water boils away!), but you'd need a
thermocouple amplifier shield, the output voltages are far too small to read without one.
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