Voltage Divider

[hotpointer]

Hi All.. and thanks in advance

I have written a programme for the Arduino thats uses a 10k resistor and a 10k ntc voltage divider.

on the breadboard using the arduino, a lcd screen shows the temp . this works fine

on a purpose made Pcb using a atemega 328 etc  the temp on the lcdscreen fluctuates  and is unusable

i dont really know what i am doing but i have put a 10Uf capacitor across the 10k resistor and this stops the Flucation.

my questions our

is this the correct thing to do ?
is there a better way if not?
why did it do this ?
and why didn't it do it when using the arduino and breadboard

thanks again
rgds John

[IanB]

I think I would have put the capacitor across the NTC, but no matter.

I guess your fluctuation is from external noise that is getting into the MCU through the A/D converter. Adding the capacitor bypasses or filters the noise out of the way. Since temperature changes slowly a low pass filter is needed on the temperature sensor to block high frequency noise. The capacitor is doing this.

There are two ways to reduce unwanted noise in a system. One is to stop the noise getting in to begin with. The second is to filter out the noise that makes it through.

To stop the noise getting in you need to know and identify what the possible sources are and use good design to eliminate them.

To filter the noise you can use various filter arrangements, but an RC filter is the simplest.

[hotpointer]

thank you

[Vgkid]

Why an ntc used in a voltage divider?

[Nerull]

A voltage divider is the standard way to use a thermistor. It outputs a temperature correlated voltage which can easily be read with an ADC.

[Vgkid]

That is what i was thinking you were hoing to use it for. A rather innaccurate rtd, unless calibrated.

[Nerull]

Thermistors have a much smaller temperature range but can be more accurate than class B RTDs when used properly. Also a hell of a lot cheaper and simpler to use.