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76  Using Arduino / General Electronics / Re: PWM as ground...is it possible? on: September 08, 2012, 01:19:12 am
Thanks a lot guys smiley Have a nice day
77  Using Arduino / General Electronics / Re: PWM as ground...is it possible? on: September 08, 2012, 12:13:24 am
Thanks for the answer and the info but you haven't really answered my question.

What i am basically asking is this:

http://arduino.cc/en/Reference/Constants
"When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, e.g. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH. "

Can i achieve the exact same thing by setting a pwm pin to 0? In other words, if a pwm pin is set to 0 then can it sink current?

Again thanks :>
78  Using Arduino / General Electronics / PWM as ground...is it possible? on: September 07, 2012, 03:51:54 pm
Guys, can i use pwm to connect to ground?
For example, when i set pwm to be 0, can the pwm pin receive current? Can it be used to saturate a PNP BJT by acting as a ground for the transistor's base? If yes, how many mA can it handle as a ground?

Thank you in advance and have a great day smiley
79  Using Arduino / General Electronics / Re: Fet or Bipolar junction transistor? on: April 09, 2012, 01:07:11 am
@spirilis
Thanx for the reply dear sir... and i am not 30...just turned 17 a week ago....i love electronics and this is a subject that highschool does not teach so i am self taught...again thank you
80  Using Arduino / General Electronics / Re: Fet or Bipolar junction transistor? on: April 08, 2012, 05:38:27 pm
Thanx for the advice sir smiley
81  Using Arduino / General Electronics / Fet or Bipolar junction transistor? on: April 08, 2012, 03:38:06 pm
Guys could you please answer me these?
>Whats the difference in use between a fet (ie mosfet) and a bipolar junction transistor (ie npn) ?
>I ve heard that fets are voltage controlled and that bipolars are current controlled. Am i correct on this? How would a bipolar react to higher voltage at the same current and how would a fet react to a higher current at the same voltage?
> When do i use an npn and when a pnp? I mean whats the great difference in use between them?
> How do i check out which is an npn and a pnp using a multimeter?
> Is there a way to know which one pin of the bipolar is which without the need to check for a datasheet? (ie turn the transistor facing its front side, the left pin is the collector, the right pin is the emitter  and the middle pin the base)
> Would anything change if the load was connected to the emitter instead of the collector?

Thanx in advance for the help and have a nice day smiley
82  Using Arduino / Motors, Mechanics, and Power / Re: Power,Voltage,Current & Resistance of a motor on: April 04, 2012, 05:20:23 pm
Thank you very much for the info sir smiley
83  Using Arduino / Motors, Mechanics, and Power / Re: Power,Voltage,Current & Resistance of a motor on: April 02, 2012, 03:06:01 pm
True... the wire was indeed tiny(1mm diameter) and the connections just touching  .One of the motor terminals was connected on the chassis (ground) through the tiny alligator clip wire and the other pole of the motor touching the + pole of the battery.  Could you please explain the wire/line thing to me?

If i got this straight you mean that because of the tiny wire and the bad connections, the wire's resistance increased when the 1A was drawn and therefore more voltage was used by the wire. So basically with 1A of current, the resistance of the wire became comparable with the resistance of the motor and therefore i had created a voltage divider circuit. Am i correct on this? Please shine some light on this as well smiley-razz
84  Using Arduino / Motors, Mechanics, and Power / Re: Power,Voltage,Current & Resistance of a motor on: April 02, 2012, 12:45:12 pm
Thank you very very very much smiley
Regarding the battery thing...
I measured the voltage at the terminals of the motor not the battery (dunno if this makes any difference). I think the battery is good since its able to start a 2liter diesel engine easily. Could the reading have changed (dropped from 12V to 8V) as a result of the back EMF induced?

Again thanks for the help...(Is there a way to vote for the best answers btw?)
85  Using Arduino / Motors, Mechanics, and Power / Power,Voltage,Current & Resistance of a motor on: April 02, 2012, 09:41:53 am
So i connected a 12v motor on a pretty big car battery the other day (12 volt,70Ah). When the motor was rotating with its shaft free (no load) the voltage across its terminals would be 12V and the current drawn 200mA. When i squeezed the shaft with my fingers (a significant amount of load applied) to the point where the motor was ready to stop, the voltage would be 8V and the current drawn would be 1A.

My Questions:
****************************
>Could you please explain this to me in terms of both the power law (Power = Voltage x Current) and Ohm's law (Voltage = Current x Resistance)?

>Is there such a thing as lower resistance for motors? (if the equation V=IxR is applied, in the first case [no load] the resistance is 60 ohms which then drops to 8 ohms in the second case [full load])

>Why did the voltage drop from 12volts to 8 volts? (i was using a pretty huge source of stable DC energy)

>Am i right on this? : "The only two factors determining the current drawn by something is the voltage supplied to that something and the resistance of that something. If the voltage is steady (or drops), the resistance has to also drop in order for the current drawn to increase "

Any "light" to my question is well appreciated. Thank you in advance smiley
86  Using Arduino / Sensors / Re: Current on any pin (anaologue or digital) on: March 03, 2012, 01:50:11 am
So what you guys are basically telling me is that i don't need a current limiting resistor on any pin (whether analogue or digital) defined as input as long as i am using the arduino's 5v supply

If i am going to use any external 5v or higher voltage supply then a resistor would need to be put in series with the input pin in order not to fry the chip right?

If i was going to do something like that would this schematic work? Would i need the 300 ohm protecting resistor? (sorry for my crappy drawing skills i did it on a mouse pad)
87  Using Arduino / Sensors / Re: Current on any pin (anaologue or digital) on: March 02, 2012, 05:26:34 pm
"because it is the pin that *draws* the current from the 5V; the 5V does not force any amount of current"

Isn't the amount of current drawn by a particular something controlled through the resistance of that something? I mean the Ohms law V=I*R
Taking into consideration that the voltage is a constant 5V supply, the only thing that can define current is the resistance right?
If the input pin has a high resistance then very little current will flow or be drawn by and vise versa isn't it?

Again thanks a lot man :>
88  Using Arduino / Sensors / Current on any pin (anaologue or digital) on: March 02, 2012, 04:08:41 pm
Guys, i would like to ask whether i should connect any current limiting resistors on pins defined as inputs, for example on an analogue or a digital pin in order not to fry the chip? In the schematics, when a potentiometer is connected on an analogue pin , acting as a voltage divider, there are no resistors protecting the analogue pin from excessive current. If the potentiometer is throttled all the way up and the input voltage is 5v then there is no resistance protecting the pin from over-current. Why is that so? Why would we use a resistor when setting a pin as an output (eg a digital pin powering an led would be connected to a 250ohm resistor) but not when using the same pin as an input? If i would need to use any resistors what values would be suitable? And lastly would it make a difference if i used a 30 k potentiometer instead of a 5k or a 10k one?

Any answers are appreciated smiley
Thank you
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