analogRead over a certain time

Question

I would like to read an analog value using analogRead, save this value and compare it to an analogRead value 5 ms later. How would this code look? Because giving a variable the value of analogRead(A0); would mean it is constantly changing, making it impossible to compare two values.

thanks in advance

Answer 1

The simplest and crudest method:

int val1 = analogRead(A0);
delay(5);
int val2 = analogRead(A0);

if (val2 > val1) {
    // It went up (for example).
}

Answer 2

You just need to copy the value into another before you overwrite it with analogRead(A0) and then compare those two variables.

int prev_value = 0;
int value = 0;
unsigned long prev_read_time = 0;

void setup() {
    prev_read_time = millis();
    value = analogRead(A0);
}

void loop() {
    if (millis() - prev_read_time > 5) {
        prev_read_time = millis();
        prev_value = value;
        value = analogRead(A0);
        if (prev_value != value) {
            // value changed
        }
    }
}