Hi All,
I have making a gadget for my home. I connected two leds and a temperature sensor over a ethernet board. When a turn on one led the power going down ( about -0,02 w) and the sensor readiing changes, about +1ºC, if i turn on two leds the power going down about -0,04 w and the sensor reading go up about +2ºC.
It is normal? How i can correct this behaviour?
Best regards
How is the Arduino powered ?
What exactly are you measuring when you say
the power going down ( about -0,02 w)
Sorry my poor english,
I connected my arduino board at power suppy of 4.8v and monitored the circuit with a multimeter. When the leds is off arduino provide 3,3v with leds off, when one led is on provide 3,0v, when two leds on provide 2,98v.... the temperature sensor going up about 3-4 ºC the leds is OFF or ON
This is independent of the power supply source, with USB connection success too.
4.8 volts is really too low to ensure proper operation of the Arduino.
See http://arduino.cc/en/Main/arduinoBoardUno
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable.
Augh... 
thank you for your note!
I allways thought that Arduino required 5V, like USB connections. I will test with 9v.
Trebol-a:
Augh...
I allways thought that Arduino required 5V, like USB connections. I will test with 9v.
The Arduino does require 5V, but when it gets it from USB, it goes straight to the VCC pin on the Atmel chip. When you power it externally, through the power plug, it goes to a regulator circuit, which needs a couple of volts over the regulated voltage to operate properly.
Ok, thank you for your comments!
I have changed the power supply to 12v, but the problem remains. =(
Now Arduino offer about 4.92v , when 1 leds is HIGH the circuit offer 4.8v, there are about 3 degrees in TMP36 sensor !! If I use two leds the temperatura variations are 6ºC!!
Any suggestions are wellcome!!
Any suggestions are wellcome!!
I think it's time you posted a schematic. From the symptoms, I'd guess you don't have any current limiting resistors with the LEDs, causing excessive current to be drawn, resulting in the voltage drop.
PaulS:
I think it's time you posted a schematic.
Yes, I will make my scheme but this variations allways happens in any simple scheme, look a simple leds connected to pin digital #13
I hope that the schematic that you draw is clearer than the video. I can't see a current limiting resistor in line with that LED, so I'm assuming that there isn't one, which makes the readings consistent. An LED without a current limiting resistor is a short circuit.