# NTC Sensor Acquisition Schematics explanation?

Thread Starter

#### Onaizit

Joined Aug 5, 2020
3
Hi all, I came across this acquisition schematics but I can't understand how it works. For NTC sensors I have always seen voltage dividers or Wheatstone bridge.
Note: The I4 input of the micro is an adc input
I would be very thankful if someone could explain me how is this supposed to work?
Thanks you

#### ericgibbs

Joined Jan 29, 2010
10,470
hi O,
Welcome to AAC.
R1 and the NTC are a simple voltage divider, non-linear response.
E
BTW: R2 and C2 are a simple filter

Thread Starter

#### Onaizit

Joined Aug 5, 2020
3
hi O,
Welcome to AAC.
R1 and the NTC are a simple voltage divider, non-linear response.
E
BTW: R2 and C2 are a simple filter
Thank's you very much for the fast and precise reply! I have another little doubt what's the purpose of C1?
Thanks you

#### ericgibbs

Joined Jan 29, 2010
10,470
hi O,
If the 5V supply was electrical 'noisy' C1 would be used to filter out any noise.
Are you planning to use the circuit with a MCU > ADC.?
E

Thread Starter

#### Onaizit

Joined Aug 5, 2020
3
hi O,
If the 5V supply was electrical 'noisy' C1 would be used to filter out any noise.
Are you planning to use the circuit with a MCU > ADC.?
E
The circuit is already implemented and yes is the acquisition for an MCU > ADC.
I just started studying how to read electrical schematics so I took a schematic of a board and I started from the acquisition part that seemed the simpler.
I am not new to mathematics around electronics but I never designed circuits so I struggle a lot to read them and understand them properly.
Thanks you for your answers it were really appreciated

#### ericgibbs

Joined Jan 29, 2010
10,470
hi,
OK,
When you start programming ADC function, you will see that the value of R2 can slightly effect the ADC 'd value, because R2 is in series with the internal impedances of the MCU and it will effect the charge time of the ADC's internal capacitor.
Often C2 is added so that the charge on C2 helps maintain the ADC pin voltage during the internal ADC sampling period, so limiting the voltage drop across R2.

When you are ready, post your circuit and a clip of the ADC program and we can advise that you have the optimum setup.

Do you have the part number of the Thermistor you plan to use.?
E

#### MrChips

Joined Oct 2, 2009
21,651
Here is another perspective.

Remove C1 and C2. Allow noise to be sampled.
Replace R2 with a zero-ohm connection.

Your noise is most likely line frequency noise.
By choosing your ADC sampling frequency carefully you can reduce the effect of line frequency noise. By allowing random noise into your samples and performing signal averaging you may be able to add extra bits to your ADC resolution.