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3496  Using Arduino / General Electronics / Re: arduino after applying to high input voltage on: November 17, 2013, 08:31:12 am
Alas over-voltage damage is usually board-wide and uneconomic to repair
(well you'd need a hot-air desoldering station and experience with SMT components)

Being pro-active with a multimeter checking voltages before connecting up is wise.
3497  Using Arduino / General Electronics / Re: Help identifying crystal please on: November 17, 2013, 08:26:17 am
Markings depend on the manufacturer - is there any indication of the manufacturer?
3498  Using Arduino / General Electronics / Re: Analog signal transmission on: November 17, 2013, 08:24:46 am
Thanks for your response.
Please correct me if I am wrong. Shielded/unshielded twisted pair requires differential signal with current flows in opposite direction in order for the cancelling effect to take place, which leads us back to my original question. How would ones generate differential signal out of a single ended signal? Thanks.

Just route both wires to ADC channels, read both and take the difference.  Any voltage drop
in the supply ground to the sensor will be compensated for this way.  Depending on the
bandwidth you want add some capacitance across the wires at the receiving end.  Basically
have separate signal and supply ground wires, and connect them only at the sensor (sending
end).  Twisted pair for signal / signal-ground, twisted pair for supply / supply-ground  should

In a an electronically noisy environment (lots of motors, mains etc) then a better scheme
may be needed (generate true differential signal, or put an ADC at the sensor end so only
need to send digital signals).
3499  Using Arduino / General Electronics / Re: LMH6559 Buffer chip problems on: November 17, 2013, 08:18:37 am
Why use an analog buffer for a logic signal?  There are logic buffers specifically for
this purpose and you can get 4 or 8 in one package too.
3500  Using Arduino / General Electronics / Re: RFID 125kHz PCB antenna on: November 17, 2013, 08:12:51 am
What is better? Circle or square PCB antenna?

Define better - to me better means its resonant at the correct frequency with its load
capacitor...  Better might also mean you use 2oz copper rather than 1oz to reduce losses...

A coil has inductance whether its circular, square, hexagonal or the outline of Australia!

For PCBs square or octagonal is usually easier to layout...
3501  Using Arduino / Programming Questions / Re: Combining Sketches on: November 17, 2013, 08:02:56 am
Fortunately its easy to go back and edit code tags into your post
// then it will look readable and be in a scrolling window
3502  Using Arduino / Programming Questions / Re: when #include in included file: file not found on: November 17, 2013, 08:00:40 am
Sorry for that silly question...

I just tested:
#include "/usr/share/arduino/libraries/DigitalToggle/DigitalToggle.h"

This also works and is, maybe, an alternative solution ...

An incredibly brittle solution - absolute pathnames don't belong in source files,
late bind them at configuration time.

The Arduino IDE makes you #include all .h's in the sketch file (.ino), so just do
that.  You can always #include them in the included files too, but they also need
to be referenced at top level (the Arduino environment copies everything referenced
to a clean temp directory I think, before compiling, so you must name all the files
in the standard place.
3503  Using Arduino / Programming Questions / Re: Arduino 022 - Errors with current avr library. on: November 17, 2013, 07:55:58 am
The most important change from 0022 to 1.0.x is for the
includes, you need to change

#include "WProgram.h"


#if defined(ARDUINO) && ARDUINO >= 100
  #include "Arduino.h"
  #include "WProgram.h"

There are a few other changes but this needs to be done first.
3504  Using Arduino / Programming Questions / Re: VirtualWire wrapper around send function on: November 16, 2013, 09:10:41 am
You can't (easily) do pointer arithmetic on references so they are safer to work with.  Most
bugs in C programs are due to erroneous pointer arithmetic and lack of array bounds
checks I think.
3505  Using Arduino / Displays / Re: Alternative to the UTFT and UTouch libraries? on: November 16, 2013, 09:07:16 am
How much of the space is due to the font?
3506  Using Arduino / Displays / Re: 4.3" TFT LCD Touch Screen and Arduino Mega on: November 16, 2013, 09:05:10 am
There is more than one SD library to experiment with, but first check all the signals are
intact and at 3.3V level.  These TFT/SD modules never seem to have level-shifting on the
3507  Using Arduino / Displays / Re: Need some help with TFT display. on: November 16, 2013, 09:03:13 am
I'd advise against buying any TFT that doesn't come with full information on the
interface, life is too short.  Knowing its a SSD1289 chip isn't enough as that can
be configured for at least 6 types of interface, 8,9,16 or 18 bit parallel and 3 or 4
wire serial.  You also need to know for sure if the logic signals are 5V or 3.3V...

For ease of interfacing I'd strongly recommend the serial type for Arduino - parallel
can be driven faster but for a small screen its not such a problem and 8 bit parallel
needs 13 wires to drive (8 bit data, nCS, nRESET, D/C, nWR, nRD).  Using the hardware
SPI on an Arduino at full speed to drive a serial TFT is pretty fast.
3508  Using Arduino / Motors, Mechanics, and Power / Re: Driving multiple mosfets from one output on: November 16, 2013, 08:15:28 am
When you parallel MOSFETs you need enough gate resistance on each to
stop differential oscillation.  For two MOSFETs use a 330 ohm resistor on each
gate (limiting total current on the pin).  The larger the gate capacitance the
more important such current limiting resistors become - those MOSFETs have
about 6nF effective gate capacitance (28nC charge for 5V drive) which is more
than a logic signal is normally expected to drive directly.

If you want fast PWM you'll probably need a MOSFET driver chip to keep
switching losses managable.
3509  Using Arduino / General Electronics / Re: How to do voltage referencing? on: November 16, 2013, 08:06:40 am
The only way to have a switchable AREF of 5 or 3.3V is to actually switch the AREF
pin between 5V and 3.3V.

This could be done with an analog switch chip under program control, or a couple of
logic-level(*) p-channel FETs (drain to AREF, sources to 3.3V and 5V.

An analog SPDT switch is safer as you don't risk shorting the 5V and 3.3V rails together.

(*) one would need to turn on with Vgs=-3.3V

You could simply live with a reference voltage of 5V and lose some precision for
the 3.3V signal.
3510  Using Arduino / Programming Questions / Re: Adafruit JPEG Snapshot sample coding on: November 16, 2013, 08:01:15 am
So how are we to know which print statements you removed?  Try posting both the
working and non-working sketches in full so the difference can be seen...
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