Each bit is received in: 1/16mhz = 62,5 nanoseconds
Very unlikely as the code (e.g. serial.print(val, DEC)) takes far more time to execute. 57600 baud means 5760 chars per second can be send, so the time between the above samples is at best in the order of 1/5760 sec ~~ 174 microseconds. Further the digitalRead also takes some time ....
based upon my assumption that the three -sometimes 4- zeros form one logical LOW => one real bit is in the order of 3.25 x 1/5760 == 0.00053 second. So the signal could be a 2Khz signal (which is quite a reasonable number). Below code to sample at this frequency (not compiled or tested)
void setup()
{
Serial.begin(115200); // as fast as possible
pinMode(40, INPUT);
}
unsigned long last = 0;
void loop()
{
unsigned long t = micros();
if (t - last >= 500)
{
last = t + t - last - 500; // the t- last - 500 is to prevent drifting ...
int sensorValue = digitalRead(40);
Serial.print(sensorValue, DEC);
}
}
Can you test this code and look if the pulses make more sense?