I have two LM35 sensors, a 2x16 LCD screen with backlight, and a speaker.
The speaker is to sound an alarm when a predetermined temperature has been reached. When this alarm activates (PWM Pin 9), I have noticed that the voltage being read can fluctuate.
The same happens when I power the backlight on the LCD module.
Is the problem because I am powering the LCD module and the LM35 from the 5v and GND ports on the board?
Is there a way to filter out these spikes?
I have had a similar problem, with an external ARef. Connect 100nF + 10mikroF to ARef pin.
I have tried that, along with putting a couple of 100nF and 10uF on the Vo and GND of the LM35.
Noise is still present though. :-/
If a decoupling with capacitors does not help, try to think about "groud loops". Connect grounds of all items (Arduino, alarm, lcd) in one common point on the power supply. The same for their Vcc.
I think I might have found the fault: I was running all of this off the USB port, as soon as I used an external power supply there was not noise.