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5806  Using Arduino / General Electronics / Re: SPI Flash capacity and speed on: April 26, 2013, 05:06:50 pm

So please forgive my n00bness but I'm a little confused about capacity specs of flash. It seems to be specified in Megabits, not megabytes. I thought Megabits were reserved for measurement of speed not capacity?

Memory chips can be specified as bits, bytes or whatever (many early DRAM chips where bit-wide so bits was natural).
Bytes is universal for packaged storage devices like discs, USB sticks, CDroms, because at that level no one is interested
in how the data is stored.

For comms bits or baud are mainly used for actual wire-protocols (like ethernet), but when talking about bus interfaces to mass-storage,
bytes tends to be more common (talking about disc write speeds, for example)
5807  Using Arduino / General Electronics / Re: Turning Arduino on and off using momentary switch? on: April 26, 2013, 04:59:32 pm
Usually the way this is done is by using a microcontroller to handle the push switch and control the main
power supply to the whole device - a small amount of power is needed to run the power-switch monitoring
circuit all the time.

It can be implemented in discrete CMOS logic too - but microcontrollers are more flexible and can do
software-debouncing.

So to do this to an Arduino you could use another Arduino (switching a MOSFET perhaps).  Not necessarily
useful.   There are ways to send the Arduino into sleep mode while still monitoring a pin - perhaps a better
approach...
5808  Using Arduino / Programming Questions / Re: Error in reading analog pins. on: April 26, 2013, 04:49:09 pm
An unconnected input pin is basically an antenna - you are seeing signals picked up from
nearby circuitry.  Drive that pin from a sensor and it'll follow the sensor (which is a much stronger
signal source).
5809  Using Arduino / Programming Questions / Re: help needed with adding a rotary encoder on: April 26, 2013, 04:46:21 pm
You looked here already?? http://playground.arduino.cc/Main/RotaryEncoders
5810  Using Arduino / Motors, Mechanics, and Power / Re: Stepper toggle possible? on: April 26, 2013, 11:33:34 am
Quote
Is this possible,


You would have to arrange a multi way switch or set of relays to switch the motors in and out of circuit
Not something many people want to do.

And of course physically breaking the connection to a powered up stepper winding is likely to
both burn out the stepper driver and weld your relay contacts shut - unless you power down the
driver before switching.

The first rule of stepper motors is don't disconnect a powered up motor...
5811  Using Arduino / General Electronics / Re: Position of Back EMF diode on Relay on: April 26, 2013, 11:28:28 am
More importantly the inductance and loop area will increase the further the diode is from the coil - leading to
more radiated interference.
5812  Using Arduino / General Electronics / Re: Voltage reading on a disconnected wire ? on: April 25, 2013, 06:28:21 pm
Pull up to 5V at the Arduino end if you are connecting to an Arduino pin.   I'd recommend a pretty strong pull-up because its
a long cable run - especially if the cable isn't shielded.
5813  Using Arduino / Programming Questions / Re: Arduino MEGA Serial Communication using TX2 and RX0 on: April 25, 2013, 06:23:52 pm
Just so that everyone can see what I am talking about, I am attaching another image here where I had connected the LED driver with Tx1 and the comparator output to Rx3. Now I put light on one of my sensors using a cellphone flashlight and you can see the LED glowing in the picture. Can anyone give me a sane explanation for this? There is no program running on the board obviously, since it is not powered. It has to do something with the internal circuitry, does anyone here have any idea about this?

You've created a very expensive piece of wire using the MEGA's input protection diodes, but that's not exactly useful is it?
5814  Using Arduino / Programming Questions / Re: Alarm not in tune with time on: April 25, 2013, 01:15:23 pm
I suggest you first re-factor the code.  Move all the UI code (setting alarm times) into a separate function
or functions.

If any routine is more than a page long then its a candidate for splitting up into smaller logical units - otherwise
you'll end up with spaghetti code than noone can understand clearly.

Having done that repost the code if its still misbehaving.

You have checked that

1) the RTC is actually telling the right time?
2) the code isn't stuck in one of the many while loops of your UI code? (those are a bad idea,
   its easy to get stuck in a loop so that the rest of the system is unresponsive - use if statements,
   remember that loop() keeps getting called -  so long as no function called by loop can take too
   long to execute (or get stuck in a loop), then every part of the system will get attention regularly.
5815  Using Arduino / Project Guidance / Re: programing the Eval AD5930 ebz on: April 25, 2013, 01:07:38 pm
The documentation appears to be here: http://www.analog.com/static/imported-files/eval_boards/47694415155145AD5930EB_0.pdf

Seems to have options to either control the chip from a USB interface or directly from headers (which is what you'll
need for the Arduino, since it can't host USB).
5816  Using Arduino / General Electronics / Re: Voltage reading on a disconnected wire ? on: April 25, 2013, 12:58:24 pm
A disconnected wire is floating - the only thing defining its voltage is leakage through the voltmeter and
leakage in the wiring.  30m is a long cable run, plenty of leakage possible.

You probably need a 1k pull-up resistor on the N/O relay contact to provide stable output when its open?
5817  Using Arduino / Motors, Mechanics, and Power / Re: confusion on chosing motors on: April 25, 2013, 09:19:39 am
I presume you'll be buying a spindle, not making one, so I'll ignore that aspect.

The XYZ motors should be bipolar high-performance stepper motors - this means winding resistance in
the 0.5 .. 3 ohm range.  You'll need suitably rated chopper stepper drivers for them, which depends on
how big and powerful the motors are, which in turn depends on your leadscrews and linear bearings and
intended performance.

If you are not going to cut metal then you can get away with less torque on the motors.  If you don't want
particularly fast rapids then a lower supply voltage and lower performance steppers can be used.  Hint:
the larger the machine the more rapids speed matters.

So without more information about the sort of leadscrews and intended performance I can't say much more.
Certainly they will be either NEMA17 or NEMA23 steppers, 200 steps per rotation, 4-wire bipolar, but how
much torque, how fast - these I can't guess.  The Z-axis might not need as large a motor, but it simplifies
things if all axes are the same.
5818  Using Arduino / General Electronics / Re: My ground wire was on fire please help me on: April 25, 2013, 09:09:05 am
Quote
Perhaps if you posted your schematic of how you had things hooked up, that might help us.

I'd go further and say posting a schematic should be a given - verbal descriptions of circuits are not usually
detailed enough, or even correct.  A photo or two of the setup is also a very useful thing - and better than
no schematic at all.
5819  Using Arduino / General Electronics / Re: LTC490 in RS485 on: April 25, 2013, 09:05:34 am
RS485 is a multi-drop bus - so long as each end of the line is correctly terminated you can place a RS485
driver anywhere along it.  Perhaps your Arduino is at the middle of the line, so each end goes off to a separate
slave?  That's fine, just terminate the slaves (since they are at the ends).
5820  Using Arduino / General Electronics / Re: Power supply outputs 0mA ?? on: April 25, 2013, 09:02:59 am
It is up to the device to 'draw' current.   The obvious question is how did you measure current?  If you simply plugged your meter in without a load you were shorting the supplies.

Which you should not do, it should be said, unless you know the supply has automatic current limiting - you may have
blown a fuse or other protective component if you short a supply out - in other words it might have been working till
you "tested" it.
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