I'm trying to control the speed of a DC current motor with PWM.

I use an arduino UNO to send PWM signal to a mosfet Velleman vma411 to change the average tension of a my motor which is wired to stabilized power supply (about 10V). In order to get the rotational frequency of my motor, I have a hall effect sensor next to the rotational axis. Each half turn the sensor changes value (either 0 or 5V). To detect the changes I use attachInterrupt() to detect the changes.

When the arduino is not sending any PWM signal, the frequency measured is perfectly fine (I verified it using an oscilloscope). BUT when I send PWM signal to my motor, the frequency makes no more sense (about 1 value out of 3 is 10 times higher than the expected one).

To solve this issue I tried three different things :

• putting a capacitor (between 100 microF and 2200 microF) between the arduino and the mosfet sig port,
• using a average value of the last 10 measured frequencies,
• adding a numerical filter,
• using one ground pin for the mosfet and a different one for the sensor port,

Nevertheless any of those ideas really worked for me.

I suppose this may be due to some electrical reflection issues? Maybe should I change my mosfet or use a L298N?

Thanks in advance

My code which goal is to measure accurately the rotational frequency while sending a PWM signal to the mosfet:

/*
alimentation du capteur : 4V
mesure précise jusqu'à au moins 10V
*/
//ports
int rotation_port = 3;
int mosfet_sig_port = 11;
int debug_port = 10;
//mesures :
volatile long t_new;
volatile long t_old;
volatile long res;
volatile float frequence;
volatile float old_frequence;
// asser
float rapport_cyclique = 127; //entre 0 et 255
void setup() {
 pinMode(rotation_port, INPUT_PULLUP); // pour interrupt
 attachInterrupt(digitalPinToInterrupt(rotation_port), capteur_hall_changement, FALLING);
 pinMode(debug_port, OUTPUT);
 pinMode(mosfet_sig_port, OUTPUT);
 Serial.begin(115200);
 old_frequence = 100;
}
void capteur_hall_changement() {
 t_new = micros();
 res = 1.0 / (t_new - t_old) * 1000000;
 if (res/old_frequence <= 1.5) {
 frequence = res;
 old_frequence=frequence;
 }
 t_old = t_new;
 Serial.println(frequence);
}
void loop() {
 // Envoi du signal PWM sur la sortie numérique mosfet_sig_port
 analogWrite(mosfet_sig_port, int(rapport_cyclique));
}