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5761  Using Arduino / General Electronics / Re: Old stepper motor Pinout? on: June 05, 2013, 03:49:31 pm
The typical way to drive these is with a darlington array with free-wheel diodes like the ULN2803, but any switches will do
if they can handle the voltage and currents involved and there are the relevant diodes.
5762  Using Arduino / General Electronics / Re: problem in dc motor need a push to start on: June 05, 2013, 03:46:23 pm
Any chance of some schematics?

Some things to note:

1. The motor is a 3V motor, 4 1.2V batteries is 4.8V.
And the L298 will lose 2.5V or more, its not a great choice for low voltage motors.
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2. The stall current is 2.1A - that is how much current is needed to get it moving from stationary
Stall current is the current it takes when the motor is prevented from running (rotor locked in place) and
its given its nominal voltage in full.  Its equal to  nominal voltage / winding resistance.

The current needed to get it running from stationary should be about the same as the no-load current,
this is due to frictional losses mainly.
(or if under load it depends on the nature of the load).
Quote

Is there any load on the motor, or is it just free-running?
5763  Using Arduino / General Electronics / Re: Receiver's Noice Input =K*T*BWeq ? on: June 05, 2013, 03:40:03 pm
Sorry, got completely confused there, its k T bw, the ln term comes in signal to noise ratio.
5764  Using Arduino / General Electronics / Re: internal resistance of atmega 328 on: June 05, 2013, 03:37:02 pm
I am using voltage regulater IC 7805 to give supply to arduino but it gives higher current supply.I want to know the internal resistance of atmega 328 so that I use resistance in between the digital pin and 7805 to lessen the current

Ohms law doesn't apply to active devices, in general.  It applies to conductors, semiconductors (if uniform, no PN junctions), electrolytes. 
Batteries are basically made of plates and electrolyte and the internal resistance there is largely due to the ohmic resistance
of the electrolyte I think (although this is by no means constant with time / temperature or age).
5765  Using Arduino / General Electronics / Re: Strange problem with wireless transceiver module on: June 05, 2013, 03:32:21 pm

lambda=c/f right?
Then lambda is 12,5cm, which means that i have to look for objects with a lenght of 6.25cm(lambda/2), 3.12cm(lambda/4) and 1.56cm(lambda/8). Right?

No, only wires that are (very slightly longer than) multiples of lambda/2 will act as resonant reflectors.  Anything conducting object larger than about lambda/4 will reflect and scatter signal though, and resonance of random shapes will be hard to predict.

Anything in the near field of the antenna will become part of the antenna system - in particular the ground plane of the module
is very important here.  And antennas are directional and polarised, so you can lose a lot of signal through bad placement.


5766  Using Arduino / General Electronics / Re: Old stepper motor Pinout? on: June 05, 2013, 03:17:26 pm
Anything else on the label?

Its almost certainly a 5-wire unipolar stepper motor, and there will be 4 windings to a common lead, all
should be the same resistance, probably in the 10 to 50 ohm range.  What is the voltage to the motor
(it might say somewhere in the scanner) - often 12V, 24V or around that.

If it is a 5-wire unipolar then none of the leads will be ground though.
5767  Using Arduino / Programming Questions / Re: Compiling error in SoftwareSerialExample of Arduino 1.0.5 on: June 05, 2013, 03:07:34 pm
Which board, which OS?  Works for me.
5768  Using Arduino / Motors, Mechanics, and Power / Re: 5 wires unipolar stepper motor + L298? on: June 05, 2013, 03:02:25 pm
You need to drive them so as not to cause current between the windings, which means knowing
what you are doing to each winding for each phase of stepping - suggests you need to control
all of them (enables can just go to 5V anyway of course).

PWM is not going to possible to microstepping is right out.

Normally a 5-wire motor would be driven unipolar though, hence the caveat.
5769  Using Arduino / General Electronics / Re: Problems with DC motor noise with proximity sensor. on: June 05, 2013, 02:57:22 pm
Its trial and error for things like this, values for decoupling and noise-suppression aren't usually very critical.

If the wires to a motor aren't twisted together its well worth doing that to reduce EMI as well.

Shielded cable to the sensor can help too, as can decoupling on the motor supply.
5770  Using Arduino / Project Guidance / Re: Talking to open collector bus serial device on: June 05, 2013, 02:49:22 pm
You must not call Serial.read() until you've checked there is at least one character in the
buffer with Serial.available() - otherwise you'll just see nonsense.
5771  Using Arduino / Project Guidance / Re: Cave Exploration: Capturing left-right-up-down from a series of sensors on: June 05, 2013, 02:46:18 pm

A tethered swimming/amphibious robot with a camera, compasss and pressure transducer might
be a more useful approach, but making a waterproof device would not be that simple...

Alternatively if you have a 9 DoF IMU that can orient to the water flow, you could sample the flow direction at
regular spacings down the cave (if its flooded there).

5772  Using Arduino / Project Guidance / Re: New to Arduino with a simple problem. on: June 05, 2013, 02:18:53 pm
That all depends on the motor controller - what current does it take for instance?  Has it opto-isolator
inputs?  Datasheet?
5773  Using Arduino / General Electronics / Re: MOSFETs for a 24 v system on: June 04, 2013, 04:09:29 pm
I thought "source" doesn't imply a polarity.  "source" v. "sink" is relative to ground, ground doesn't have to
be the negative rail?  Its just like "emitter" in NPN / PNP transistors.
5774  Using Arduino / Sensors / Re: ds1620 digital thermometer question on: June 04, 2013, 04:02:38 pm
DS1620.h is not ds1620.h
5775  Using Arduino / Sensors / Re: how to increase the sensitivity of sound sensor on: June 04, 2013, 04:00:11 pm
Datasheet please...
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