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Author Topic: Signal controlled LED board  (Read 1667 times)
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Pravi
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« on: July 10, 2012, 12:34:10 12:34 »

Hi,

I have seen a Digital Red LED Light Module board from DFRobot. The confusion is, how can we design a board where a signal from one pin can power up a LED without using a transistor? The board has three pins, 1. Input, 2. Power and 3. GND. If it is only two pins, then one pin can be to Vcc (or Gnd) and the other can be connected to a signal pin in microcontroller (which can be set to HIGH or LOW). But how really does this board from DFRobot work with three pins? If anybody has a schematic, kindly share. I have a similar doubt for another board which is a "Digital Push Button" which again activates with three pins.

I guess it might be simple, but to the knowledge of electronics I have, it sounds difficult. I need this to implement to one of my projects and sounds really difficult.

Link for LED board is : http://www.dfrobot.com/index.php?route=product/product&filter_name=led%20board&page=2&product_id=490
Link for Push button is: http://www.dfrobot.com/index.php?route=product/product&filter_name=button%20switch&product_id=73

Thanks,
Pravi
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pirvcb
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« Reply #1 on: July 10, 2012, 01:21:18 13:21 »

Nothing seems so obscure...
Actually, micros give out sufficient current to drive a led (pics up to 100 ma, dunno exactly about AVR, the arduino case). I guess, the three pins issue is for standard connection to arduino board or so. Also, i've seen a 470 ohm resistor placed on the led board that can be used to drive direct the led limiting the current using the 5V out of micro's pin. Also seems some jump place to make other configurations (true or NOT logic) i suppose.
But not active components in picture....
Same for push buttons board: i suppose the main use is for connection standard to other arduino's boards and setting for true or false command.
OR WAS JUST A JOKE?
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Pravi
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« Reply #2 on: July 10, 2012, 03:46:02 15:46 »

Quote
micros give out sufficient current to drive a led (pics up to 100 ma, dunno exactly about AVR, the arduino case)
Well, even AVR gives sufficient current to drive LED's.

Quote
Also seems some jump place to make other configurations (true or NOT logic) i suppose.
These are used to place other components. The interesting thing about *this* particular board is that the same board can be used for multiple sensors : Tilt sensor, Magnet detector, LED board, Push button, IR sensor, ..... and many more. Hence the different jump places.

Quote
i suppose the main use is for connection standard to other arduino's boards and setting for true or false command.
This is the very reason I am interested in. The board (custom developed) I have also has three pins (Sig, Vcc and Gnd) which makes plug and play easy.

Can someone justify three pins or give a schematic of these two boards please? if the issue is to just drive LED from a microcontroller, then I know how to. The issue is how have they designed the board to use three pins instead of just two. (without a transistor)

Quote
OR WAS JUST A JOKE
   It truly isn't Wink
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« Reply #3 on: July 10, 2012, 04:04:19 16:04 »

Quote
(1) control terminal (2) power supply (3) ground
that board has 4 smd jumper, and two of them has been solder short. so I can say that it is a configurable board.

maybe the customer need output a high level to light the led. in another case,want output a low level to light the led.

it is a good way for the seller and customer.

In general, the board will configure to high level input to light led. but if you do not able to identify it , ask the seller first.

almost mcu can source or sink a 20mA led on a pin.
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May be I expressed the wrong meaning, sorry for my bad english. Please correct it for me if you can.
Pravi
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« Reply #4 on: July 10, 2012, 04:09:18 16:09 »

Quote
that board has 4 smd jumper, and two of them has been solder short. so I can say that it is a configurable board.
Wow, that's really a good catch (and design of course). Never identified that.

Quote
maybe the customer need output a high level to light the led. in another case,want output a low level to light the led
True. But how does it work with three pins? In any case, (with SMD jumpers) if user decides to light with MCU low, then the other pin must be high. But what is the third pin for?

Is there someone who has got this board, or atleast can give a schematic of how it works with three pins?
« Last Edit: July 10, 2012, 04:13:24 16:13 by Pravi » Logged

pickit2
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« Reply #5 on: July 10, 2012, 04:33:56 16:33 »

reason for 3 pins? why not ask at www.dfrobot.com
Code:
///Arduino Sample Code
///www.DFRobot.com
///Last modified on 16th September 2010

int ledPin = 13;                // choose the pin for the LED
int inputPin = 3;               // Connect sensor to input pin 3


void setup() {
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare pushbutton as input
}

void loop(){
  val = digitalRead(inputPin);  // read input value
  if (val == HIGH) {            // check if the input is HIGH
    digitalWrite(ledPin, LOW);  // turn LED OFF
  } else {
    digitalWrite(ledPin, HIGH); // turn LED ON
  }
}

http://www.dfrobot.com/wiki/index.php?title=Digital_White_LED_Light_Module_(SKU:_DFR0021)
« Last Edit: July 10, 2012, 04:39:23 16:39 by pickit2 » Logged

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Pravi
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« Reply #6 on: July 11, 2012, 06:11:47 18:11 »

Quote
reason for 3 pins? why not ask at www.dfrobot.com
Lol... If they had shared the schematic or the reasoning for three pins, I would have simply not asked here. But sadly they haven't and hence approached here as I have received most help here. Normally most hardware over there is opensource, but this one doesn't seem to be.
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