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1  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
2  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.

??
3  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
4  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
5  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
6  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.
7  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
8  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
9  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.
10  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
11  Using Arduino / General Electronics / Re: help needed on this schematic ( well pump monitor ) - no arduino .... for now on: May 09, 2014, 03:40:43 pm
thanks, I'll have a close look at it
12  Using Arduino / General Electronics / Re: help needed on this schematic ( well pump monitor ) - no arduino .... for now on: May 09, 2014, 02:06:37 pm
thanks for the answer.
replacing the low-water shutoff circuit shouldn't be that difficult. As far as I can see, if there is current through RE and EB, than there is water in the well, if not, the pump must be stopped. All I need to know is the minimum value, under which I must shut off the pump.
The pump is turned on when the pressure switch is ON ( if no lack of water, indeed).
But I'll do that in several weeks, when I have time.

For now, I'm trying to figure out what causes this weird behaviour, which component is the culprit, and change it.
What makes it difficult is that it is a "random" breakdown, not reproducible .

Buying a whole replacement system would be too expensive for the house owner ( I'm only an occupant smiley-wink ) .
And now, I'm frustrated, I need to understand smiley-wink

PS : Actually, I'm not "inexperienced", I studied and worked in electronics ... okay..... long time ago smiley-wink , and I've been working on PLC for several years. But sure, I need to practice and remember .....  smiley-mr-green

edit : typo correction
13  Using Arduino / General Electronics / Re: help needed on this schematic ( well pump monitor ) - no arduino .... for now on: May 09, 2014, 11:22:20 am
arf.... nobody has an idea of which component might be faulty ?
maybe the transfo : when it works, I hear no noise, but when it doesn't work, there is a "bzzzzz" (50Hz, I guess) which seems to come from the transfo.
14  Using Arduino / General Electronics / Re: Does Arduino start automatically on: May 08, 2014, 02:04:57 pm
yes
15  Using Arduino / General Electronics / Re: help needed on this schematic ( well pump monitor ) - no arduino .... for now on: May 08, 2014, 01:24:22 am
BTW, there is no thermal relay , the '95' connexion goes to A2 of the contactor .
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