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241  Using Arduino / Project Guidance / Re: Driving stepper drivers on: July 10, 2014, 06:16:32 pm
Why a sine? I'm curious.
242  Using Arduino / Project Guidance / Re: How to calibrate a speedometer? on: July 10, 2014, 06:15:27 pm
You need to dust your dash. ;')
243  Using Arduino / Project Guidance / Re: i need advice in my project on: July 10, 2014, 06:12:05 pm
Kudos to you for getting an early start!
244  Using Arduino / General Electronics / Re: Question, wire as a variable resistor on: July 10, 2014, 06:10:31 pm
You said:

Quote
measure the resistance of the led

How do you propose to do that? And why?

The link and quote you gave does not calculate resistance of the LED, it assumes 2V drop and calculates the -current limiting- resistor.
245  Using Arduino / General Electronics / Re: Minimising power consumption on soil hygrometer sensor on: July 10, 2014, 05:33:43 pm
I would not be surprised if the probes don't last a year, due to corrosion aided by electrolytic corrosion.
246  Using Arduino / Project Guidance / Re: The Bat Ultrasonic Location System on: July 10, 2014, 03:55:15 pm
only difference is frequency.

Or the wavelength  smiley

Someone at a makerspace I was at had printed and put up a miniposter illustrating hertz vs cycles per second, but on a lin-log scale. I laughed out loud, then I found out that the person who had posted it was dead serious and didn't get the joke.

Like this:



That particular image is from this website. To newbies: please note the date when the given formula was written.

http://www.brainerdham.org/Tips/CPS_to_Hz_conversion.html


247  Using Arduino / Motors, Mechanics, and Power / Re: How to use NPN transistor with powerful MOSFET on: July 10, 2014, 03:40:24 pm
I have a few questions.... why the 0.033uF (or do you really mean 0.033mF, which is 33uF?) capacitor? Why the voltage divider? Why such a high series resistance?

I'd lose both the capacitor and the 10k resistor, and use a 220 ohm resistor in place of the 5K resistor.
248  Using Arduino / General Electronics / Re: Circuit Correct? Help me! on: July 10, 2014, 02:11:50 pm
4.7k is pretty high resistance, it is going to turn off that P MOSFET rather slowly. That may be your head problem.

Change R2 to 470 ohms, that's about 10mA base current, and R3 to 100 ohms. What is the battery supplying power to the motor?

If that is a little 9V battery, that is not going to be enough current. So when loaded, not only will the voltage drop, the Vgs will drop. And that is NOT a logic level MOSFET, it is rated at 10V from Gate to Source (-10V on the gate relative to the source)
249  Using Arduino / General Electronics / Re: Question, wire as a variable resistor on: July 10, 2014, 12:00:05 pm
Ohm's "law" only holds true for linear resistance. At least in any meaningful fashion. It doesn't really tell you anything useful to "calculate" resistance of an LED at 20mA, because that number of ohms changes with current and voltage.
250  Using Arduino / General Electronics / Re: "a quasi resonant inverter" on: July 10, 2014, 09:16:16 am
I suppose because LTSpice won't run on a phone. And that app has a lot of eye candy. LTSpice has a steeper learning curve. I prefer it because it is also -immensely- powerful, especially compared to this particular simulator.
251  Using Arduino / Project Guidance / Re: The Bat Ultrasonic Location System on: July 10, 2014, 09:13:27 am
Yes. Radio, light, IR, UV, X-rays, gamma rays are all the same thing, only difference is frequency.
252  Using Arduino / General Electronics / Re: "a quasi resonant inverter" on: July 09, 2014, 07:30:39 pm
Yes, definitely need to use something like a polyester film capacitor. A bipolar electrolytic would probably not survive long there.
253  Using Arduino / Project Guidance / Re: The Bat Ultrasonic Location System on: July 09, 2014, 06:44:51 pm
It is only sound if it travels by vibration of atoms or molecules. If it travels by photon, it is radio or light, or ionizing radiation. You can have radio waves at 1kHz, and sound at 2MHz. It isn't the frequency that determines which it is.
254  Using Arduino / Project Guidance / Re: multple (5) stepper motors controlled with arduino via android on: July 09, 2014, 06:41:02 pm
I notice the original poster has only posted here in this thread, once more in Aug 2012, and never again. So I don't know if we'll get an answer.
255  Using Arduino / Project Guidance / Re: multple (5) stepper motors controlled with arduino via android on: July 09, 2014, 06:39:12 pm
I'm curious, too.

The Shapeoko2 CNC mill manages to control 3 steppers with an Uno. There are four steppers, but two are doing exactly the same thing. The firmware on the Uno is called GRBL and it is open source.

I just bought a RAMPS 1.4 board, it is a breakout for five A4988 based stepper drivers with some other handy things like temperature sensor input and output for heaters, it plugs into a Mega. Meant for 3D printers, it isn't usually called on to run more than four steppers at once. I bought it to see if I can redo GRBL to run it.
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