Hello! Good day!!
Please, I need help T_T
It's about my temperature sensor (Lm35). When I'm using USB to power up my arduino, the reading of the temperature appears to be stable, and normal. From 32, 31, 32, 32... so on. (in Celcius)
But the problem arises when I use an external 9v power supply adapter. The temp reading fluctuates from 32, 19, 11, 36, 45, 25...etc. (in Celcius)
Please I need immediate attention! I really appreciate if you have any solutions for this.
Send help! THANKS!!!
for 3 years i bought twice on aliexpress LM35 and both time it was something else remarked as LM35.
you probably got the same.
are you in Afrika?
Post an annotated schematic of your circuit, show all connections including power and ground. Please note any wire(s) that are over 10" in length.
If your sketch doesn't have analogReference(INTERNAL); in setup(), then that could be your main problem. Many example sketches on the net for the LM35 and TMP36 are crap.
Leo..
The LM35 and TMP36 have minimal current sink capability which can cause problems with the input impedance of the Arduino.
Philippines, sir. Anyways, got any thoughts about my problem?
Well things work fine when under USB power but things go wrong when using your external 9.0 volt power supply. I am assuming a 9.0 volt power supply capable of whatever your current needs are. Best guess less any further info is your external 9.0 volt supply has excessive noise on it. Less a scope you can't really look for any mains ripple but since things work using USB power and get flakey using your external supply my best guess is a poor external supply.
Ron
Don't forget that bypass cap (range 0.01 - 0.1uF)
Reading this may help
1 Try this Smoothing | Arduino
2 Applying what has been learned in the readings of the NTC sensors of the controller
Hi, @zawsze
Can you please post link to specs/data of the 9V plug pack.
Can we please have a circuit diagram?
An image of a hand drawn schematic will be fine, include ALL power supplies, component names and pin labels.
Have you a DMM?
If so measure the 5V pin on the controller with the 9V adapter.
What model Arduino are you using.
Thanks.. Tom.. 
What's that? Isn't the output of an LM35 strictly a DC level?
Yep, 0 to 1000mV @ 100°C, sounds like a cheapy, unregulated wallwart with lots of ripple..
Try powering the Arduino through the USB socket, with a 5volt cellphone charger.
Leo..
HI,
Keep all three leads to the LM35 as short as possible and direct to the UNO.
Don't let the leads share any current flow with other peripherals.
An image(s) of you project would help with understanding component placement.
Thanks.. Tom..
I see you use a 12volt relay module. Post a link..
When powering the relay module on JD-VCC and GND, with the jumper removed, you should not have a ground connection to the Arduino. Only connect relay VCC to Arduino 5volt, and the inputs to the Arduino output pins.
You must have that line I told you about in post#5 in your code.
Code without it will be unstable.
And don't forget diodes (DC) or snubber circuits (AC) on the relay loads.
Leo..
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