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5746  Using Arduino / Project Guidance / Re: 20 bit output Arduino Duemilanove on: March 05, 2013, 09:25:32 am
shiftOut takes a byte so you'll need to call it repeatedly for each set of 8 bits.  Only after
shifting out to all the 595's should you pulse the latch pins.
5747  Using Arduino / Sensors / Re: Which gyroscop for an auto balanced skateboard? on: March 05, 2013, 09:21:07 am
A standard 6DoF IMU would be a good choice, can then maintain orientation with DCM or quarternion method - there are
many forums about this, mainly on quadcopters, but the principle is the same - combine short-term gyro input and long-term accelerometer
input to estimate orientation.

For a simple one-axis balancing robot a single axis gyro and two-axis accelerometer is enough, but i think these skateboards
use tilt in the other axis as a control input for rounding bends?
5748  Using Arduino / General Electronics / Re: Digital pots like AD5206 on: March 05, 2013, 09:00:53 am
For any particular device you need to check the datasheet but in my experience all digital pots are switched resistor networks, so
no trouble with any analog signal that is within the supply rails and within the bandwidth of the device.  That particular pot
has quite high stray capacitance on its analog terminals, note, so it doesn't stay linear much past the audio range, especially the 100k
part.
5749  Using Arduino / General Electronics / Re: What are chips like the MEGA2560 used for in real-world applications? on: March 05, 2013, 08:52:05 am
I see the applications for the low-end 8 bit controllers that Atmel makes and the ARM processors too, but I don't understand the niche for the ones in the middle like the 2560.  It's fairly expensive and has a small number of pins and raw compute power and memory compared to ARM.  What is it used for?  It seems the only slam-dunk application would be legacy low volume apps where compatibility with existing code is paramount.  What sort of products do we know the 2560 is in except for the Arduino Mega?  And does the go for XMEGA and AVR32 as well which seem to fall in the same boat?

Its not as expensive as you think - commercial products will be buying multiples of 10,000 and the price breaks for high
volume are substantial - qtys of 500+ already about half unit price...  Typically PCB board area (and associated manufacturing
costs and enclosure) is more expensive than the chips on it unless exotic devices are used.

Some of the market will be for gadgets developed on smaller AVR processors, but which have become more featureful in
successive versions and the developers move to a microcontroller that has more memory which is code-compatible with
previous versions.  The cost of re-engineering the hardware and software to switch between vendors is not trivial and
carries plenty of risk compared with staying with tried/trusted tech - especially in a competitive market where keeping
up with market developments is a race with time.

Also when a range of similar products is developed it is desirable to base all of them on the same software base - so using a range
of uControllers from the same vendor pays off - the cheaper/less featureful units can shave cost by using cheaper versions.  The more
advanced units in the product range will demand more memory, I/O, interfaces etc...

The uControllers vendor that can provide a wide range of software-compatible controllers will be favoured in the long run.
5750  General Category / General Discussion / Re: String Overflow on: March 05, 2013, 08:32:19 am
Its not C!, some flavour of Basic?
5751  Using Arduino / Motors, Mechanics, and Power / Re: Solenoid valve. on: March 04, 2013, 06:25:32 pm
You will need to find a 12V solenoid valve or stick with using a mains-rated relay to control it.

In theory a solenoid valve could have its coil re-wound, but I suspect taking one apart will ruin it...
5752  Using Arduino / Programming Questions / Re: Can I set pinMode other than analog and digital pins? on: March 04, 2013, 06:18:23 pm
ATmega32 ??   Do you mean ATmega328 or ATmega32U4 ?

Basically pinMode works with pins that are defined via the pins_arduino.h file for the relevant variant.
5753  Using Arduino / General Electronics / Re: Very simple resistors question on: March 04, 2013, 06:12:05 pm
If the LEDs are different colours you are likely to run into problems this way - if the same
colour then it will work better (but current distribution won't be as balanced - this may not matter)

Another approach is to PWM the supply to the existing LEDs - reducing the average brightness
without changing the resistors.
5754  Using Arduino / General Electronics / Re: What kind of oscilloscope should I buy? on: March 04, 2013, 06:03:54 pm
There are some really tiny breadboard mountable scopes which look enormous fun: http://www.gabotronics.com/development-boards/xmega-xprotolab.htm - I haven't tried one personally but the price is reasonable for what it is I think.
5755  Using Arduino / Programming Questions / Re: DS1307 and writing problem into 56 internal ram on: March 04, 2013, 05:49:16 pm
Can you clarify which library and version?  And do you already have code (its much easier to
give concrete examples relating to existing code)

Conceptually the DS1307 looks like a 64 byte non-volatile RAM with special behaviour of the
first 8 addresses.  The I2C interface allows specifying a starting address and then writing or reading
consecutive bytes from that point.
5756  Using Arduino / Sensors / Re: analogRead() reading non-existent fluctuation? on: March 04, 2013, 10:57:11 am
You probably need low-pass filtering on the sensor inputs - something in the range 1nF to 10nF to ground for both
green and white wires ought to help - the leads to the sensor may be picking up noise, the sensor itself may
be noisy.

Multimeters use integrating ADCs so they effectively low-pass filter down to 1Hz or less bandwidth - the ADC on
the Arduino has a bandwidth more like 10kHz.
5757  Using Arduino / Motors, Mechanics, and Power / Re: Long range PTZ turret on: March 04, 2013, 07:16:18 am
The DC motor has no encoder so no accuracy at all.  The actual precision of the stepper motor will be limited by
the backlash in the gear system (which I believe is not 64:1 as they claim, but a ratio very close to that - I seem
to recall a thread about this a year ago).
5758  Using Arduino / Motors, Mechanics, and Power / Re: dc motor as a variable resister? or potentiometer? or encoder on: March 04, 2013, 07:11:55 am
Not a normal motor.
Perhaps a brushless motor, but I'm not sure.


Not really - although for a constantly turning shaft you can measure the number of electrical cycles
and act as an encoder - but stationary motors produce no signal, and very slowly moving one's almost
nothing.

What are you trying to detect/measure?
5759  Using Arduino / Displays / Re: SSD1963 controller with 7" TFT (horizontally mirrored image) on: March 04, 2013, 07:04:18 am
The most promising option seemed to be:

0x36 Set_address_mode

BUT

NOTHING happens no matter what I change the value to, in fact if I comment out the line it makes no difference.

Address mode only changes the behaviour on sending multiple pixels - IIRC the UTFT library sets up bounding
rectangle before drawing lines / blocks and then sends the right number of pixels - the bounding rect ensures
all the pixels end up in the right place whatever scan-direction is used.

The gate-scan and source-scan bits are what you need to find.
5760  Using Arduino / Displays / Re: Uno and 7" LCD on: March 04, 2013, 06:59:26 am
21 level shifters???
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