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1  Using Arduino / Motors, Mechanics, and Power / Re: Question about stepper motor and l298n (for this particular project) on: July 23, 2014, 11:51:30 am
There are many places to buy motors, but remember to check all the specifications
before buying - find some possibles and post their details here, someone will be able to
confirm suitability.  I would imagine NEMA17's are the size to go for as they are plentyful
and more than powerful enough (remember you get to choose the size of timing belt
pulley.)

Tip:  rubber timing belt is far better than polyurethane belt for small low power
systems, polyurethane (such as T2.5 and T5 belt) is much stiffer and rated for
large forces and high power and needs lots of pretension to eliminate backlash.
2  Using Arduino / Motors, Mechanics, and Power / Re: Help with a Stepper Motor on: July 23, 2014, 11:44:27 am
You need to breakdown your task into separate parts.

Communication from computer to Uno

Control of stepper from Uno

tackle each task on its own, when each is working combining them should be
more obvious.
3  Using Arduino / Motors, Mechanics, and Power / Re: Making Of 4 Wheel Robot on: July 23, 2014, 11:42:09 am
The Arduino motor shield controls 2 motors upto about 1A (peaks of 2A for short
time).

You probably need more powerful H-bridges, and for low voltage high current
MOSFET H-bridges would be much better than Darlington ones.  Pololu.com
(among others) has a range of motor drivers for DC motors of various ratings.
4  Using Arduino / Motors, Mechanics, and Power / Re: Serial monitor crash when relays switch on main power on: July 23, 2014, 11:39:18 am
Its vital to route the high current load wiring (lamp mains cable?) well away from
all signal cables - running wires in parallel to the mains will guarantee interference
in my experience, shielded or not, because induction is not affected by shielding (which
only protects against capacitive pick-up).

If you have ground loops that's a very efficient route for induced voltages to affect
your circuit.  Adopt star-grounding for all the low-voltage wiring.

Do you know if your mains load is inductive?  Snubber network may be required.
5  Using Arduino / Motors, Mechanics, and Power / Re: arduino motor shield on: July 23, 2014, 11:30:58 am
Can you clarify that you need to send data to the Arduino and have it use
that data to control a motor?  Can you give more details?
6  Using Arduino / Motors, Mechanics, and Power / Re: Does this MOSFET implementation look correct? on: July 23, 2014, 11:29:41 am
AREF can be switched internally to the internal reference, or to Vcc, or left floating.
Just give it its decoupling, that's why its pinned out.  See the docs for
analogReference()
7  Using Arduino / Motors, Mechanics, and Power / Re: Troubleshooting a L293D Circuit on: July 23, 2014, 11:27:47 am
Have you cut traces on the stripboard in all the places you need to?
8  Using Arduino / Motors, Mechanics, and Power / Re: Question about stepper motor and l298n (for this particular project) on: July 23, 2014, 11:26:40 am
That system doesn't have any position feedback, its open-loop and will perform
differently with different loads even.  Having said that that heavy gearmotor will
be less sensitive to load than some DC motors.

If you want definite position control with a stepper motor you have two options,
either pick a high resistance motor that can be driven from 12V via a L298 or
similar dual-H-bridge, or choose a low-resistance motor that is suitable for
chopper drive (such as via an A4988).

High resistance typically means 40 ohms or thereabouts, typically labelled
something like "12V 0.25A"
low resistance would be 1 to 3 ohms or so, perhaps labelled "1.2A 2 ohm"

High impedance motors are often unipolar and easy to drive with an ULN2803
or similar, low impedance motors are always bipolar (4 wire), and with too
high a current rating you may struggle to keep the driver cool.  High impedance
voltage-driven motors will run slower in general.

Occasionally you see medium impedance motors, around 10 ohm, which are
possible to drive from 6V or so via H-bridge (or via a chopper drive), which
gives more options.
9  Using Arduino / General Electronics / Re: ADC false readings on: July 23, 2014, 11:11:12 am
The ADC on the Due has a bandwidth of MHz, so there is a lot more noise bandwidth.

What bandwidth do you actually want to sample the signal on?  Make sure you LPF
the signal going into the ADC pin (or sample frequently digitally LPF it afterwards).

You will find the ADC is noisy on the Due as it shares power with the digital
parts of the chip (alas).
10  Using Arduino / General Electronics / Re: Arduino Due: Minimum reading of "20" on analog inputs on some PCBs on: July 23, 2014, 11:05:24 am
You might have to consider a ZIF socket and S.O.T. of the SAM chip, although that
complicates manufacturing as you'd have to process waffle trays of them yourself.

You might want to investigate parts from other suppliers should there be bad batches
around.

Have you correlated performance against date/batch codes on the chip?
11  Using Arduino / General Electronics / Re: measuring curren from a chip... on: July 23, 2014, 10:49:28 am
As I said earlier:
Quote
7805 quiescent current is 3mA
12  Using Arduino / Motors, Mechanics, and Power / Re: Arduino Motor Shield Help on: July 22, 2014, 12:05:08 pm
The motor shield is for driving DC motors, not bipolar stepper motors.  If you want
a powerful fast stepper motor you need a current-controlled chopper-drive controller
with a high voltage supply driving a low-impedance motor.

If you only need a slow stepper then a high-impedance motor with fixed-voltage
dual-H-bridge controller is enough.

Perhaps its time to say what you are actually trying to achieve?
13  Using Arduino / General Electronics / Re: Mega2560 max current question........... on: July 22, 2014, 12:00:15 pm
You need to connect all of the power/ground pins anyway, or the chip isn't guaranteed
to work, since they all require proper decoupling right next to the pins.  This is generally true
of all logic chips where multiple power / ground pins are there to provide a low-inductance
path the the PCB and provide signal return paths for nearby digital pins.

14  Using Arduino / General Electronics / Re: Which transistor to control 12V (350mA) Solenoid Valve? on: July 22, 2014, 11:55:14 am
the 1N4007 isn't really an overkill. It is used as free-wheeling diode and it should protect against the inductive current when switching off the power on the coil. The current that is produced in this moment is much higher then the original source current. Here you can have 100 - 200 V for a very short moment. That's why it is always a good idea to use a 1N4007 for that purpose.

No, the current at that point is exactly the original source current, since inductances
resist change in current.  The voltage is generated to maintain the current, should there
be no easy route for the current the voltage will force a route.

The important property of the diode is fast turn-on.  Most diodes are reasonably
fast at turn on (turn off is another matter), but larger diodes are slower, so 1N4001
is probably better than 1N4007.  For 350mA you could even use a 1N4148 which has
a repetitive peak forward current rating of 450mA (although that's rather close for
comfort).  Even a fairly slow diode is likely to limit the voltage spike to 10V rather than
1000V, so in general they just work.
15  Using Arduino / General Electronics / Re: measuring curren from a chip... on: July 22, 2014, 11:45:54 am
Place the multimeter (current mode) across a switch in the supply lead.  Once all is working
open the switch and the meter measures the current.  If you need to switch
current range, close the switch, change the range, open the switch - that way the
chip won't reset or power-cycle due to range-changes.

This matters when measuring small currents as the low-current range on the meter
uses a large shunt resistance which is unable to carry enough current to reboot
the processor, but which is needed to measure tiny sleep-mode currents.

The shunt resistor on ground of 7805 makes no sense to me - the ground pin
must be at ground potential or the output voltage could be too high.

A 7805 will totally dominate the power consumption of the board in sleep mode,
there are special low-quiescent-current regulator chips available - look for the
magic word "micropower" in datasheets.

Microcontrollers in sleep mode are typically 5 to 0.1 uA, 7805 quiescent
current is 3mA, about 1000 times bigger.
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