I bought a light sensor (LDR), but he got stained, what it means? It is used? Or is residuum of time?

I must give back? I have to clean up or something?

I bought as new, so I tested one of the LEDs will not turn on.

I bought the (Mercado Livre in BRAZIL).

The product is: http://www.gbkrobotics.com.br/exemplo-produto/p7-sensor-de-luz-com-leds.pdf

I pay R$8 BRL (equivalent aprox. $2 dollars) but, i just wanted to know if he had something I could do, because only shipping was R$ 13 BRL ($4 dollars)

  • I'm starting with Arduino, thx

enter image description here

  • Do you have a picture of the front, or a datasheet/part number? It could be that the LED is in the wrong way around, or that it is simply broken. The stains could be due to moist. Have you bought the item off e-bay? Then you should contact the seller, give him pictures of the stains and defective LED. They're usually very kind and if all else fails, you can open a PayPal dispute (if you really want to get your money back).
    – aaa
    Apr 15, 2016 at 6:29
  • Hey, man! I update the question, please check? Apr 15, 2016 at 12:47
  • 1
    I doesn't look that bad in the photo. Try cleaning it with some alcohol or acetone on a tissue. Otherwise it's probably inconsistent thickness in the blue soldermask that was applied. This wouldn't affect it's function anyways.
    – Gerben
    Apr 15, 2016 at 13:05
  • It's a light sensor. So try covering the sensor (check if the lights go off) and try shining a flash-light on it. That might make all three LED's go on.
    – aaa
    Apr 15, 2016 at 14:56

1 Answer 1


I've read you post a couple of times and I get the impression you would like this board to work, so here are some quick check to try and find the fault.

  • You need a bread board
  • An arduino
  • A 200-300 ohm resistor.
  • Some wires. About 6 hands :)

Connect the board ground to the breadboard. Then connect the to the resistor. Then connect that to the power supply ground.

Take the positive off the power supply and touch it to the LED1 pin and check LED1 lights up. Repeat with 2 and 3.

Switch every thing off

Connect the Positive to the Vcc connection of the board. Connect a wire between Arduino A0 and "Sinal Analog"

Load this sketch

   void setup() {
   void loop() {

When you cover the LDR it should read a lower number when you shine a light on it should read a higher number.

Turn everything off again, and if you have a multi meter test the resistance of the resistor on the board it should be 300 ohms, but I can't remember which way to read the bands and it might be 10K ohms, which would be a problem.

If anything doesn't work then they can all be fixed for a few cents and you don't need to worry about the discolouration.

Hope that helps you.

  • Thank you for your help. The store sent me a new sensor. The LED3 dosn't work )): Apr 19, 2016 at 19:31
  • If you don't need to return the broken one then replacing LED three should be very easy (if you get it the right way round) and then you have two :) Apr 20, 2016 at 12:47

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