Signal controlled LED board

[Pravi]

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

[pirvcb]

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?

[Pravi]

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.

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.

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)

OR WAS JUST A JOKE

   It truly isn't

[DreamCat]

(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.

[Pravi]

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.

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?

[pickit2]

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)

[Pravi]

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.