Compatibility with JSN-SR04T-2.0 sensor

[bilbolodz]

Actually it's not a library issue but: I'm trying to run these sensor into serial mode but without any success. Any comments/remarks are welcome.

[stoduk]

I don't know this sensor but the link I found below suggests this only supports ping/echo mode (like the basic HC-SR04).

Are you sure it supports serial mode?

http://artofcircuits.com/product/jsn-sr04t-2-0-water-proof-ultrasonic-module-distance-measuring-sensor

[bilbolodz]

According these PDF: https://www.google.pl/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiu1eSxsNTWAhUCaFAKHdkkDmIQFggqMAA&url=https%3A%2F%2Fwww.jahankitshop.com%2Fgetattach.aspx%3Fid%3D4635%26Type%3DProduct&usg=AOvVaw0v_VKu_EYJoKstjsEl-ct8 it has serial mode. I've v2.0 version.

[stoduk]

It looks like it can operate in three modes (ping/echo, constant serial, serial on request). It lacks the temperature compensation of the US-100 so you'll lose some accuracy there, but serial mode should make it far more accurate/precise by avoiding the latency issues.

However, the manufacturers of this have gone with a slightly more complex protocol - which I can imagine would be helpful in the continuous mode but is less obviously required in the on-demand mode.

It wouldn't be rocket science to add support for this, but without a JSN-SR04T it would be impossible to test. Feel free to make the changes and send a pull request though - it shouldn't be much more than adding a new Init parameter to show which protocol is being used (US-100, JSN-SR04T, etc.) and then the receive handling needs to decide whether it wants 2 or 4 bytes and we should check the start byte/checksum as they are there.

[bilbolodz]

I know it but so far I'm not able to put it "into serial mode", that I've asked about any experience with these module. Tonight I will connect logic analyzer and I will try to check "raw TTL signals". I will keep you updated for any progress.

[bilbolodz]

Working code (standalone code not library mode) for "Mode 2" (R27 47k resistor):

#include <SoftwareSerial.h>

#define receiveTimeout 90 //Dane wysylane są co 100ms

SoftwareSerial mySerial(2, 3); // RX, TX

static boolean dataReady = false;
static boolean dataTimeout = true;
static byte ndx = 0;
unsigned int distance;

byte buforek[4];

unsigned long lastReceiveChar;

void readDistance();

void setup() {
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  Serial.println("Start!");

  // set the data rate for the SoftwareSerial port
  mySerial.begin(9600);

}

void loop() { // run over and over
  readDistance();
  if (dataReady) {
    Serial.print("Distance: ");
    Serial.println(distance);
  }
}

void readDistance() {
  if (lastReceiveChar + receiveTimeout < millis ())
  {
    dataTimeout = true;
  }

  if (mySerial.available() > 0 )
  {
    if (dataTimeout == true) {
      ndx = 0;
      dataTimeout = false;
    }

    buforek[ndx] = (byte) mySerial.read();
    lastReceiveChar = millis();
    ndx++;

    if (ndx == 4) {
      ndx = 0;

      if (buforek[0] == 0xff && ((buforek[0] + buforek[1] + buforek[2]) & 0x00ff) == buforek[3])
      {
        distance = buforek[1] * 256 + buforek[2];
        dataReady = true;
      }
    }
  }
}

[stoduk]

I'll close this for now - your code will be there if anyone wants it, but until someone has time to make a full fix and the equipment to test it we can't fix it.