[SOLVED] AnalogRead problem

I have a voltage divider connected to PA4 pin of STM32F103RE

Voltages on PA4 oscillate from 2.0 to 2.6 volts, but the analogRead on PA4 going way off.

Here is the code
void setup() {
pinMode(PA4, INPUT_ANALOG);
Serial.begin(9600);
}

void loop() {
int analogValue = analogRead(PA4);
Serial.println(analogValue);
}

What are the resistor’s values ?

[Pito – Thu Oct 26, 2017 8:36 am] –
What are the resistor’s values ?

12 VCC(+-2) – 10k + 1.5K – GND

If Vin is between 10 and 14 volts, Vout should be between 1.3 and 1.8V approx.

http://www.calculatoredge.com/electroni … divide.htm

How do you get 2.0 to 2.6V ? I’m not sure I understand your circuit.

[ahull – Thu Oct 26, 2017 9:49 am] –
If Vin is between 10 and 14 volts, Vout should be between 1.3 and 1.8V approx.

http://www.calculatoredge.com/electroni … divide.htm

How do you get 2.0 to 2.6V ? I’m not sure I understand your circuit.

Could be, I saw the waves in oscilloscope, nothings goes above 3v and was around 2v. The voltage divider seems not the problem, but the analog values changing are. Voltage doesn’t go 0 at voltage divider while analogRead returns it.

12 VCC(+-2) – 10k + 1.5K – GND
Divider’s input voltage:

Input Voltage.JPG (67.52 KiB) Viewed 522 times

Double-check the GND wiring, it seems your GND is floating (some breadboards do not have a continual GND rail handy).

the wiring is good, hardware seems all good. I think the problem is in reading analog.

try with just an AA battery to PA4 and ground ?
then maybe AA+ to 1k/2k to gnd, pa4 to junction of the R’s
that should demonstrate or eliminate an analogue read problem, barring a bad crimp in the wires
stephen

.. also try the analog read on some different pins (perhaps PA0, PA1 or PB0) to see if the problem is perhaps just a dodgy solder joint on the pin in question.

Sorry guys, it was fault in schematics, so is in hardware.

AC battery