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3496  Using Arduino / Motors, Mechanics, and Power / Re: Powering the Micro Servo 9g FS90 on: July 08, 2013, 04:43:12 pm
Assume each servo peaks at 1A or so.
3497  Using Arduino / Motors, Mechanics, and Power / Re: VEXTA PH256M-33-C3 Step motor on: July 08, 2013, 04:41:41 pm
For high speed stepping you need a bipolar motor with low resistance / low inductance windings and a high-voltage
supply powering a chopper-drive circuit.

The high voltage supply overcomes the back-EMF of a fast spinning motor, the chopper drive controls the current to the
correct value and the low inductance winding allows fast response to the steps.  High voltage also helps with fast response
since rate-of-change of current is equal to V/L.

Typical "high performance" motors would be 0.6 ohm 5A windings and 80V to 120V powered driver.  That's rather
extreme though, something like ~ 1 ohm 2.5A windings and 24 to 48V supply would be pretty standard.

The fast stepping mainly helps with the "rapids" for CNC, you've never cut at very high speeds (without an awesomely powerful
spindle motor!).
3498  Using Arduino / Motors, Mechanics, and Power / Re: Is it safe to run a motor from this voltage regulator without a diode? on: July 08, 2013, 04:33:04 pm
Hey guys,

I had some voltage regulators made which use the first circuit in this datasheet:

And I'd like to drive a vibration motor like this off it:

I had a mosfet module with a flyback diode on it to use with 5V motors, but I had 100 of my 12V modules made and I only really needed 50 and I was thinking maybe I could upgrade the vibration motor in my project to a 12V one of the same size and use those spare 12V modules instead of spending hundreds of dollars getting more of the mosfet modules made.

The 12V modules don't have that flyback diode in them though.  They do however have a diode that would protect the switch pin and inductor, and there's a path to ground through R1 and R2.  So I thought maybe it might be okay.  Plus it's not a very large motor. 

I'd solder a diode across the pins on the motor, but there aren't any, just a couple wire leads, so it would be a bit of a pain and there's no really good place to put a diode on the module itself and I cant' trust the end user won't get the altered and unaltered modules mixed up.

So what do you think?  Will I fry the regulator quickly?  Will it survive?  And is there any chance at all of damaging my microcontroller?

You need a flyback diode across an inductive load otherwise you'll toast all the semiconductors...
3499  Using Arduino / Motors, Mechanics, and Power / Re: What hardware is required?!? on: July 08, 2013, 04:30:49 pm
You'll also have to define "silent", no motors are silent.
3500  Using Arduino / General Electronics / Re: 4 Legged capacitor?! on: July 08, 2013, 04:27:32 pm
Soooo the other 2 legs?  What do they do?

Partly for mechanical support, to protect against vibration fatiguing the other leads.
3501  Using Arduino / General Electronics / Re: Critique my proposed circuit (12v opto isolated) on: July 08, 2013, 04:24:06 pm
The 7805 requires decoupling capacitors on input and output.  Also the 7805 is not rated for automotive use - you may need better
protection against the spikes and noise on the 12V power - a filter to cleanup the 12V line might be a wise precaution.
3502  Using Arduino / General Electronics / Re: Will this PCB work for a 555 timer? on: July 08, 2013, 04:19:18 pm
And there should be a decoupling capacitor on the supply near the 555 or 7555.  The 555 needs a lot of decoupling,
go with the CMOS 7555 if you can.
3503  Using Arduino / General Electronics / Re: Surface Mount Crystal for Atmega328 on: July 08, 2013, 04:15:57 pm
Pretty much any crystal should work if its load capacitance is around 20pF - so long as its fundamental mode.
You pay more for better frequency accuracy and better "cut" (which affects temperature dependence of
frequency) I think.
3504  Using Arduino / Motors, Mechanics, and Power / Re: 12 volt relay at 24 volts at 20 amps on: July 07, 2013, 02:01:08 pm
well I don't need to switch 20 amps. I only need to power on the motor controllers (about 40 Ma) the relay would then stay on continuously and 20 amps would flow through the relay that was already closed. So the relay would not switch 20 amps but 20 amps would pass through the relay. Is it okay to do this as long as I avoid high current sparks?

Just assume it'll be switching 20A, because at some point that will happen (in the real world).  If you can avoid
it switching off at full current you'll extend the contact life a lot, which is great.
3505  Using Arduino / Sensors / Re: Wind speed and direction idea on: July 07, 2013, 01:59:21 pm
You couldn't be more right.

I placed a tube over the BMP085, 1cm wide, 2cm long.
I blew right into the tube it to see what the value did.
That increased the kPa by about 1.0

Blowing right into the tube isn't what happens with the actual wind.  You need to hold the tube in a stream of moving air, not
anything like the same situation.
3506  Using Arduino / Programming Questions / Re: Mega loop - sometimes slow on: July 07, 2013, 01:56:19 pm
A better way to handle this problem is to use pin change interrupts - when the first switch is switched
you record the value of micros(), when the second switch goes, subtract the recorded value from the current
values of micros() and place the result in an appropriate volatile variable (an array would be good, indexed
by key).

If no other interrupts are firing this should give accuracy as good as micros(), which I think is either
2us or 4us...

There is at least one pin-change-interrupt library out there, or you can code it yourself - basically IO
pins are organised into ports (upto 8 pins per port), and you install an interrupt routine for each port
of interest.

The pin change interrupt routine would have to first figure out which pin has changed (XOR with the previous
value from that port).
3507  Using Arduino / Programming Questions / Re: Bouncy button on: July 07, 2013, 01:44:38 pm
What kind of button - some ("tactile" pushbuttons) have a snap action and make reliable contact after initial bouncing,
whereas others require finger pressure continually to keep a contact, which is much less reliable.
3508  Using Arduino / Sensors / Re: Wind speed and direction idea on: July 07, 2013, 01:14:53 pm
Any turbulence at all will likely defeat you.  The Pitot tube pressure sensing method (tube pointing into the wind) works
at aircraft speeds, but Its sounds unlikely to have much success at low speeds.

The main problem is that pressure goes up as the square of the windspeed, so low speeds mean very small pressures.
Ultrasonic anemometers are used these days, and the time difference in ultrasonic pulse propagation is
linear in windspeed.

A google search revealed a bernouilli effect pressure system for measuring extreme winds - so clearly for high winds
pressure is a workable method.   It might be an interesting experiment to see how much signal to noise you
get for normal windspeeds using something like pitot tubes or bernouilli venturi...
3509  Using Arduino / Sensors / Re: max effective resistance for pull down resistor? on: July 07, 2013, 12:55:22 pm
If you move to high-resistances you will need to protect against electro-magnetic pick-up in the
cabling, which in practice just means adding a few nF of capacitance between the input pin and ground
at the Arduino end.
3510  Using Arduino / Motors, Mechanics, and Power / Re: Arduino not supplying enough power?? on: July 07, 2013, 12:51:40 pm
A voltage regulator is what you need.   Most 9V batteries are unable to supply suitable current BTW - use a pack of AA cells.
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