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1  Using Arduino / General Electronics / Re: MC34063 buck with large variable input? help on: August 13, 2014, 12:00:46 pm
Would ACT4088 chip be a good option?
http://www.mouser.com/ds/2/631/ACT4088_Datasheet-345917.pdf
 I really like the price and minimal components on this chip.

I know this chip has a wide input range based on the datasheet, but I still can't determine if this means you choose the external components based on a fixed input within the allowed range, or can the input be variable to the completed circuit for flexibility to the end user?

I need an input range of about 7v-24v DC, to provide 5v output, ranging from 100ma to 500ma, but 1000ma would be nice to have if possible.

any suggestions would be great.
thanks
Mike


as far as I can see, the output voltage only depends on Rfb1 and Rfb2 - 

but, the efficiency decreases as the input voltage increases, and is not good at low load current values ,  you should have a look to the typical performances curves, to see if it suits your needs .
2  Using Arduino / General Electronics / Re: what's this phenomenon called? on: August 13, 2014, 05:28:42 am
Quote
symmetrical power supply
Even if the voltages are not the same? Like +12V & -9V.

no, just for same voltages
3  Using Arduino / General Electronics / Re: what's this phenomenon called? on: August 12, 2014, 06:35:54 pm
Placing batteries in series no problem.. add the voltages.


But when you use ground between the 2 voltages we get a voltage shift, anyone know the name of this?

symmetrical power supply  (that's how it is called in french)

lool, Awol  smiley-lol
4  Using Arduino / General Electronics / Re: use 50+ LEDs and arduino on: August 10, 2014, 10:40:08 am


if i use this kind of schematic and control 10 transistors using arduino to power up 50 leds, Does this would be normal ? I'm also interested in whether 12 volt 2A power supply is enough for arduino plus LEDs?

it won't work :

1- the Leds you'll buy are pre-wired with a series resistor, for a 12V power supply - Thus you can't put 10 of them in series with a 12V power supply

2- with a npn transistor, you must put the load (here, the led and included resistor) between +Vcc and Collector, and emitter to 0v . Don't forget to put a resistor between the arduino output and the base !!
Search this forum (or google) with the words "arduino, transistor, switch" and you'll find a lot of examples .
3 - you should check the included resistor value, it will tell you how much current each led needs .

5  Using Arduino / General Electronics / Re: The terms "common emitter" and "emitter follower" on: August 02, 2014, 01:29:08 am

It's not intuitively clear to me where the terms come from... can someone elucidate please? What do they mean?

the common collector configuration is also called "emitter follower" , just because the output 'follows' the input (unity voltage gain)
6  Using Arduino / General Electronics / Re: Voltage divider on: July 17, 2014, 10:01:19 am
I strongly suggest that you don't try and divide 9V down to exactly 5V. Your battery probably charges to something higher than 9V, and if the battery dies, the charger will almost certainly drive it to a few volts over 9V.

But if you've exactly divided 9V down to 5V, that puts more than 5V, ie, more than Vcc on an analog pin. That is not a good thing to do. It will have the high resistance in series with it, but it is still not a wise idea.

.......

what about a 5V zener diode  // with R2 ?  it will protect the input
7  Using Arduino / General Electronics / Re: Power-up the arduino uno with external 5v dc through the 5v pin. on: July 06, 2014, 04:05:09 pm
Arduino uno produce 1 ampere current from the transistors.if we want more than that,
The best way to supllier the 5vdc from external sources.

??
8  Using Arduino / General Electronics / Re: Question about the transistor TIP122 on: June 29, 2014, 02:17:31 am
Hi  Jeff27,

I (or others here) could answer your questions one by one ( Ic = collector current.... Hfe = current gain etc... ) , but I think you'd better have a look here :

http://www.electronics-tutorials.ws/transistor/tran_1.html

and then here (more about darlington transistors)

http://www.electronics-tutorials.ws/transistor/darlington-transistor.html

you'll get answers to all your questions, and more smiley
9  Using Arduino / General Electronics / Re: Arduino and BD710 Transistor... on: May 23, 2014, 03:01:11 pm
hi paul, that so far worked as expected.  the led flashes for ~10 msec.

Code:

int basePin = 9;
int led = 13;

int s = 1000;
int d = s * 2;

void setup()
{
  pinMode(basePin, OUTPUT);
  pinMode(led, OUTPUT);
}

void loop()
{
  for(int i = 0; i < 2; i++)
  {
  [font=Verdana]  analogWrite(basePin, HIGH);[/font]
    digitalWrite(led, HIGH);
    delay(10);
    [font=Verdana]analogWrite(basePin, LOW);[/font]
    digitalWrite(led, LOW);
    delay(s);
  }
  delay(d);
}

??
see what happens if you replace "HIGH"  and "LOW" with different values in the analogWrite() commands smiley-wink
10  Using Arduino / General Electronics / Re: I accidentally bought non-polar 10uf caps... on: May 18, 2014, 02:13:14 pm
Quote
You'd never run into this but there are very rare cases where polarized is required to get the desired response and vise Vera's where you would think that a polarized would work as it's dc but must use a non polerized ,which is more common
??
maybe it's because english is not my mother tongue, but I can't get what you mean here   smiley-roll

edit : oups, sorry,  forget it, with ".... vice versa...." , it makes sense  smiley
11  Using Arduino / General Electronics / Re: 10k-ohm resistor between switch and ground: why? on: May 17, 2014, 10:49:22 am
Quote
I was wondering why the resistor(circled in red) is placed after the photo resistor, instead of before. If the resistance of the photo resistor were to drop to a very low value (close to 0), would there be a short-circuit because the 5V pin would be directly connected to A0? Or is there like a minimum resistance for a photo resistor?

no, ther would not be a short-circuit here. The wiring is 5v-LDR-resistor-GND , and A0 connected to the LDR<->resistor junction .

if you put the resistor between 5V and LDR, it will work, but you'll get t a reverse information :

wired as it is, if the light is brighter, the LDR resistor is lower, and the value on A0 increases .
If you put the resistor between 5V and the LDR, when the light is brighter, the LDR resistor is lower, and the value on A0 decreases.
12  Using Arduino / General Electronics / Re: Where to place a resistor. on: May 11, 2014, 12:50:46 pm
... to protect the LED

It will protect the LED, that is true.
But the main reason for using the resistor should be to protect your Arduino.
An Arduino pin is limited in the current it can output (absolute max of 40 mA.)
You should stay away as far as possible if you can, and that's the most important reason to use a current limiting resistor.


And you assume he is using an Arduino?

you should have read the OP smiley-wink
Quote
...where pin 5 on the Uno goes...
I don't think he was talking about a Fiat  smiley-mr-green
13  Using Arduino / General Electronics / Re: Questions on projects 02 on: May 10, 2014, 12:18:44 pm
each Led is connected to an arduino output, which provides 5V when HIGH. Without the resistor, the current through the Led and the output would be too high. The Led and/or the output would fry smiley-wink
14  Using Arduino / General Electronics / Re: Questions on projects 02 on: May 10, 2014, 08:20:51 am
Hi,

1) I don't know the arduino project book, but, basically, the 220 Ohm resistor is there to limit the current and thus protect the Led and the arduino output .
The current in the Led will be :  I = (5V - V led) / 220     
Vled depends on the led  (for a Red led, it is  about 1,9V )
If you replace the resistor with a wire, you'll likely fry the Led and maybe the arduino output too

2) If one side of the pushbutton is connected to 5V and the other side  to the input, yes, the input will be HIGH when the button is pressed, but the arduino inputs are high impedance inputs. Their state is undetermined when the are not connected to anything. Then if the button is released, the input is in an undetermined state .
That is why you need a pulldown resistor between the input and 0V , so that the input is LOW when the button is not pressed.
15  Using Arduino / General Electronics / Re: help needed on this schematic ( well pump monitor ) - no arduino .... for now on: May 10, 2014, 03:02:34 am
you're right, I'll do that today
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