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9 years, 2 months ago.
AnalogIn problem (pics included); strange values for temperature sensor (LM35DZ) and STM32F103RB
I'm a beginner in STM32, so please help me with the following issue:
I've made firmware upgrades, stm32 library updates, In picture one first rows readings are from a 1.28V battery the rest are from the LM35 sensor. Battery seemns ok but for LM35 I get 367mV instead of 270mV (measured with a multimeter) I don't know why the value from L35 is not ok from the uC's ADC . The connections are made like pic 3 (I use analog in A2 )
The code:
http://developer.mbed.org/users/alexlungu10/code/ADC4Home/
Text code below:
test
#include "test_env.h"
Serial pc(USBTX, USBRX);
AnalogIn analogValue(A2);
DigitalIn userButton(USER_BUTTON);
DigitalOut led(LED1);
// Calculate the corresponding acquisition measure for a given value in mV
#define MV(x) ((0xFFF*x)/3300)
void notify_completion(bool success) {
led = 0;
pc.baud(9600);
int count = 0;
bool enFlag = true;
while (1) {
count++;
if (userButton == 0) {
enFlag = (enFlag == true) ? false : true;
//pc.close();
}
if (enFlag) {
unsigned short meas = (analogValue.read_u16());
//float fl = analogValue.read() * 3300;
//float final = (float) 3300* (float) meas / 65535 ; // normal 0.0008 or 3.3v-3300mV 0,8058608058608059 3300/4095
pc.printf("%d; 16bit %hu val in mV: %d \n", count,
meas, ((meas * 3300) / 0xFFFF)); //, (int) fl);
}
led = !led;
wait(1.5f);
}
}
1 Answer
9 years, 2 months ago.
I had a similar problem with Nucleo L152 and MCP9700 (similar in operation to the LM35 sensor). Potentiometer voltage measurements were consistent with a multimeter, but with the sensor were wrong (as in your test, voltage read by the A / D was significantly too big). When I connected an oscilloscope it turned out that the input A / D signal was noisy and definitely helped capacitor between GND and input A / D. I gave RC filter 1k and 1uF. The system measures fine.