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3481  Using Arduino / Motors, Mechanics, and Power / Re: Can Arduino Uno power four 3.3 volt motors without frying the Arduino on: November 18, 2013, 10:16:25 am
I am trying to build a quadcopter with an Arduino. Can it power four motors without frying itself. Each motor draws 3.3 volts of power.

Quadcopter motors at 3.3V sounds unlikely to me.  Is this really really small?
Voltage is not power, BTW.  Typical quadcopter motors might take 5 to 20A peak,
way way out of capability of Arduino.  Normally sharing a supply between digital
circuitry and a motor is an expensive mistake.

If you provide details of the motors (link to datasheet or similar) we can understand
what you have better.

Quadcopters tend to use RC BLDCs with an ESC each, powered from a 2, 3 or 4S LiPo
battery pack and controlled via the Servo library.
3482  Using Arduino / General Electronics / Re: Motor interference and decoupling capacitors on: November 18, 2013, 10:10:33 am
The cap across the motor terminals will reduce high frequency noise from the
brushes, but don't add any capacitors between motor terminals and case, that
just makes the motor case a radiator of interference.  You can add a ground wire
to the case.  Make sure the high current wiring is all twisted pair and doesn't contain
large loops that could radiate flux.

Never share ground wires between high current parts of the circuit and the sensors.

This means that the grounds of the Arduino and the motor driver should meet once, so
that you have a star-ground from that point.  In particular if you ground the motor
case from the high current side of the circuit, it must not be connected to signal
ground of the encoder.
3483  Using Arduino / General Electronics / Re: Wafer 2.0mm 11 pin connector, where to get? on: November 18, 2013, 09:55:32 am
Something like:
http://uk.farnell.com/jst-japan-solderless-terminals/b11b-ph-k-s-lf-sn/header-top-entry-11way/dp/9491899 ??
3484  Using Arduino / General Electronics / Re: N and P channel Mosfet pairs for h bridge on: November 18, 2013, 09:52:29 am
HI there i am interested in building a 4 mosfet h briidge to  control some motors. i have come accross these ones and i was wanting to see if they are suitable to make this kind of circuit:
http://4.bp.blogspot.com/_mhuuHR0dxnU/TUmqNgeGi9I/AAAAAAAAEWo/ZJ6QFIvvEdQ/s1600/hbridge_fix_update.png

Here are the mosfets:
IRF5210 MOSFET P Channel Transistor   
STP40NF10L - N-Channel Power MOSFET Transistor   


Alas that's a bad circuit since it has inherent shoot-through which will cause
all sorts of nasty problems that will be device and supply-voltage and load-current
dependent.  The two MOSFET types have plateau voltages that are just too close
for comfort so as one starts to switch off the partner will start to switch on and
massive currents (100A?) could flow at each transition.

You always have to drive the high-side and low-side switch for an arm of the
bridge separately so one can be turned off before the other is turned on.
3485  Using Arduino / General Electronics / Re: AC basic circuit help on: November 18, 2013, 09:38:51 am
Three wires to the relay might be valid - if its a latching relay (which is a fair
choice to make).
3486  Using Arduino / General Electronics / Re: what transistors or relays do I need? on: November 18, 2013, 09:34:18 am
You just need to tot-up the currents.

Each segment has 3 strings, so 3 x 20mA = 60mA per segment.

7 segments = 7 x 60mA = 420mA, plus decimal point = 440mA,

Since multiplexing that's it.

Relays are far too slow for multiplexing, and they wear out if driven like the clappers.

You could use a constant current LED driver chip like the STP16DP05 for the
low side (one channel per segment), and then PNP or p-channel transistor for
the high-side switching via a level-shifting stage.  One such high side switch is used
per digit.

Darlington drivers will also work for low-side, such as the ULN2803, but don't
include serial-->parallel conversion so you might need a shift register as well to
save pins.

With a constant-current LED low-side driver you can lose the resistors, except that
you probably want some resistance to current-share better (or you could drive
each string separately from a constant current sink - most of these chips have
16 channels).
3487  Using Arduino / General Electronics / Re: Understanding Radio communication thoroughly on: November 18, 2013, 09:21:46 am
Some of the websites and publications for amateur radio might be a good place
for in-depth coverage of various aspects of radio technology.

I would tend to recommend getting a grounding in electromagnetic theory first -
for this the MIT lectures by Walter Lewin are a great place to start - entertaining
too

http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/

This seems a simple starting point without needing too much brain strain for
an overview of modern digital RF comms:
http://www.digi.com/technology/rf-articles/rf-basics
3488  Using Arduino / Displays / Re: Why would this lcd CGRAM address function crash my Arduino Pro Mini (Uno)? on: November 17, 2013, 04:37:18 pm
You can only determine RAM usage at runtime as stack and heap memory use is
not known at compile time.
3489  Using Arduino / General Electronics / Re: Phototransistor or Photodiode on: November 17, 2013, 04:33:25 pm
Making the resistor a log potentiometer in series with a 100 ohm resistor.  Then you
get to adjust the sensitivity as needed (the 100 ohm pretects the diode or transistor
from over-current when the pot is fully anticlockwise).

Another way is to use a comparator chip and compare the diode/resistor divider against
the wiper of a 10k pot between 5V and ground.  The Uno chip has a built in analog
comparator which is connected to certain pins (forget which, I think one of them
can be any analog pin).

If you want self-calibration then you'll have to do it in software and pick a resistor
value that gives the widest range of input voltage for likely conditions (an analog
input is needed rather than a digital one).
3490  Using Arduino / Motors, Mechanics, and Power / Re: Brushless hub motor arduino control on: November 17, 2013, 04:26:57 pm
These hub motors come with a controller - you just need to control the controller.
Reverse - you'll be lucky to find one with reverse, its not needed on a bike.

Hub motors are BLDCs with hall sensors so it isn't super-hard to build your own
3-phase bridge to drive these, but its not trivial either.  You need a 3 phase gate
driver like the FAN7388 and 6 n-channel MOSFETs with suitable ratings, protection
components and preferably a current sensor and over-current-shutdown circuit.
An Arduino can provide commutation and PWM drive.  Its not a first electronics
project however and an oscilloscope is needed I think.
3491  Using Arduino / General Electronics / Re: Mosfet H-Bridge questions on: November 17, 2013, 04:19:31 pm
Hi! I've few questions about Mosfet H-bridge.

1. Does it matter if the current rating of N and P are different? for example N is 70A and P is 100A.
You would never design any MOSFET circuit based on the current limit, you use the on-resistance to estimate power dissipation.  If you ever get close to the maximum current
you'll be needing water-cooling and large blocks of copper....  Matching Rds(on) values is
the ideal, but p-channel devices generally have 3 times the on-resistance due to hole-mobility
in silicon...
Quote

2. Is it bad having Mosfet that's rated way too much than what the load needs. Ex. 6A stall motor with 70A H-bridge.
Its not bad, its wise - you want some overhead capability if you don't want exploding
MOSFETs on current spikes.  As I said you design from the Rds(on)...
Quote

3.Can I parallel Two H-bridges? Connect the Outputs together and also the Inputs to the Base for Higher Current.

I read  a lot that's its hard to build a Mosfet H-bridge,  Why would this be harder than any H-bridges when all I have to do is
copy someone else already working H-bridge/Schematics?  Hope you guys understand my English lol. Thanks!

Its not hard per se, its just that it gets harder as the current increases and a lot harder as
the voltage increases.  You need protection circuitry that works, you need to understand
the capacitive feedback inside MOSFETs and design so that dV/dt currents don't overload
your gate driver and blow the gate oxide.  You need to understand stray inductance so
that the circuit layout doesn't allow the source voltage to bounce too far below ground
(which again can blow the gate oxide).

A 12V 5A bridge isn't too scary, but say 50V 50A and its a different game (there's kilowatts
of power available to destroy things if you get it wrong).

All big H-bridges are n-channel only BTW.

3492  Using Arduino / Project Guidance / Re: radioshack camera shield with seeed studio sd card shield on: November 17, 2013, 04:03:03 pm
Please provide links to their websites so we know exactly what shields you mean.
3493  Using Arduino / Project Guidance / Re: Fire a water drop 6 to 10" into the air? on: November 17, 2013, 04:01:14 pm
I think the droplet is likely to become a mist at the speed required to get it 6 to 8 feet in the air.

Who mentioned feet?

Yes, this is an issue even so, you get a small jet, not a drop, because there's far
more energy than surface tension can contain.

The way ink-jet print head works is to have a chamber with a diaphragm behind a
nozzle.  The diaphragm is pulsed to knock enough fluid out of the
chamber.  Refilling the chamber can probably just be done with gravity flow if the
nozzle is small enough so surface tension prevents leakage between drops.

I think nozzle sizes need to be something like 0.5mm or less, not 6mm.   Even so that's a lot
larger than ink jet printers, but you want to reach 10" so its all going to have to scale up...

http://en.wikipedia.org/wiki/Inkjet_printing#Drop-on-demand

I think there could be a lot of experimentation unless you find an existing system
documented that does something similar already.
3494  Using Arduino / Project Guidance / Re: face recognition on: November 17, 2013, 03:49:56 pm
You at least need a processor with enough RAM to hold an image!
3495  Using Arduino / General Electronics / Re: Analog multiplexer on: November 17, 2013, 08:39:51 am
If there is no other ground wire then connecting the screen to ground at
both ends doesn't create a loop - however that usually doesn't help as the
IR-voltage along the screen due to the supply current returning through it
gets added to the signal.

Often the way round this is to send signal and signal-ground at the sending end
(ie connect screen to ground at sending end), and then reference the signal to
the signal-ground at the receiving end using a differential amplifier or ADC.

Adding back-to-back diodes between signal ground and supply ground at the
receiving end is sometimes used as a protection measure (with normal noise
levels the diodes never conduct, but if there's a fault the signal ground can act
as a supply ground and, for instance, prevent electrostatic damage)
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