Category Archives: NodeMCU

Dealing with DYP-ME007Y TX spurious readings

The serial-output of the DYP-ME007Y ultrasonic range detector is pretty good when you are measuring the distance to a static object with little or no other obstacles creating ‘noise’.

However, the odd spurious reading does crop in from time to time. For example:

201cm
201cm
201cm
128cm
201cm
201cm
201cm
201cm
201cm
201cm

This is actual data, and the spurious 128cm makes no sense and needs to be ignored (rather than just taking an average). Fortunately, @JMMS-Karunarathne and @MikeMeinz wrote some code to correct for this here: https://www.codeproject.com/tips/813946/a-method-to-ignore-anomalies-in-an-ultrasonic-dist

The code takes a group of samples and counts how many of each there are. It then picks the measurement with the highest count (the ‘mode’). In the above example, there are 9 counts of 201cm – which would be returned as the measurement.

So far, so good..

However, there is a problem where all the data is rubbish. Look at this actual data:

275cm
273cm
273cm
275cm
0cm
483cm
0cm
0cm
125cm
235cm
274cm
274cm
274cm
690cm
816cm
274cm
274cm
273cm
0cm
483cm
0cm
274cm
274cm
90cm
184cm
292cm
273cm
539cm
648cm
316cm

This was produced by out-of-range measurements – the object was less than 28cm from the sensor. The measurement which occurred the most was 274cm and so the algorithm would return this seemingly meaningful result.

An improvement to the ‘mode’ routine would be to apply a ‘confidence’ to the measurement. In my code, I take 30 readings, and require a minimum of 20 of the same to accept it as a good measurement. I try this five times over, after which the routine gives up and returns a zero indicating out-of-range. This seems to work well.

Except some of the time. This looks like good data:

82cm
82cm
82cm
82cm
83cm
82cm
82cm
83cm
83cm
83cm
83cm
83cm
83cm
83cm
83cm
82cm
83cm
83cm
83cm
82cm
82cm
83cm
82cm
83cm
82cm
80cm
83cm
83cm
82cm
82cm
confidence was 16
Returning 0cm

Here 83cm was only measured 16 times. This was an absolutely static measurement on the bench, however the returned value was either 82 or 83cm (ignoring the 1x 80cm!).

The way to deal with this is to look at the readings +1 or -1 from the mode. If either the count of the mode, added to the count of the mode+1, or mode-1 adds up to at least the threshold, then the result is good.

 

DYP-ME007Y TX (Serial output) Ultrasonic Sensor interfacing with Arduino / NodeMCU

There are two main versions of the DYP-ME007Y ultrasonic module (see here to tell the difference) – this article is about interfacing and taking readings from the serial output version.

At the labs, we have been working on interfacing one of these with the NodeMCU – an Arduino-type device with built-in Wifi. This is in order to create a water tank level sensor. The automotive ultrasonic sensor lends itself to this application in that there is no need to add waterproofing – it is already there.

To interface with it we need to convert the 3.3V digital in/outs from the NodeMCU to the 5V required by the DYP-ME007Y. If you were using a 5V Arduino, you wouln’d have to do this. For us, we use a bi-directional logic level converter which is available from eBay. We bought from Electro TV Parts because they stock them in the UK and so shipping is fast.

We are only using two of the four channels on the converter. These are for the two sides of the serial connection between the NodeMCU and the DYP-ME007Y – RX and TX. The converter also needs 5V, 3.3V and GND, which are all available on a pins of the NodeMCU board.

On the NodeMCU, we then need to choose two digital pins for the serial connection, and connect these to the LV (low voltage) side of the converter. The HV side connects to the DYP-ME007Y RX and TX pins. It also needs 5V and GND.

For the serial connection, the pin assigned as TX on the NodeMCU connects (via the converter) to the RX pin on the DYP-ME007Y, and RX on the NodeMCU to TX on the DYP-ME007Y, also via the converter. That’s just how serial works!

Now on to the coding.

We use SoftwareSerial to assign the two digital pins as the TX and RX on the NodeMCU, then we are ready to read the results from the DYP-ME007Y.

#include <SoftwareSerial.h>

// pin assignments. TX on the arduino connects to RX on the sensor, RX to TX.
#define TX_PIN D3
#define RX_PIN D4

SoftwareSerial DYPSensor = SoftwareSerial(RX_PIN, TX_PIN);
const int MAX_TRY_SERIAL = 50; // how many cycles of 10ms to wait for before giving up on the sensor (up to 255)

Here you can see I am using pre-defined constants (D3/D4) for the NodeMCU in the Arduino dev environment. We also define how many times we will try to read the serial before giving up. This allows trapping of the situation were there is nothing coming from the DYP-ME007Y – like if it was not connected.

Now in setup, we start up the serial:

void setup() {

 Serial.begin(19200);
 delay(10);

 DYPSensor.begin(9600);

} // end of setup

We are also starting up the serial connection to the computer it is connected to so we can see debug information.

Our loop looks like this:

void loop() {

 int current_reading;
 current_reading = GetDistance();

 Serial.print(current_reading);
 Serial.println("cm");

 delay(50);
}

..which just calls a subroutine to read the sensor and then prints the result to serial.

GetDistance looks like this:

int GetDistance() {
 byte msb, lsb, checksum, checkcalc, tries = 0;
 int distance;

// we want a 255 which is the start of the reading (not msb but saving a byte of variable storage)..
 while (msb != 255) {
 // wait for serial..
 while ( not DYPSensor.available() && tries < MAX_TRY_SERIAL ) {
 delay(10);
 tries++;
 }
 if (tries == MAX_TRY_SERIAL) {
 Serial.println(" TIMED OUT WAITING FOR SERIAL.");
 return -1;
 }
 msb = DYPSensor.read();
 }

// now we collect MSB, LSB, Checksum..
 while ( not DYPSensor.available() ) {
 delay(10);
 }
 msb = DYPSensor.read();

while ( not DYPSensor.available() ) {
 delay(10);
 }
 lsb = DYPSensor.read();

while ( not DYPSensor.available() ) {
 delay(10);
 }
 checksum = DYPSensor.read();

// is the checksum ok?
 checkcalc = 255 + msb + lsb;

if (checksum == checkcalc) {
 distance = msb * 256 + lsb;
 // Round from mm to cm
 distance += 5;
 distance = distance / 10;

return distance;
 } else {
 Serial.println("bad checksum - ignoring reading.");
 return -1;
 }

} // end of GetDistance()

GetDistance() returns a signed integer of the distance in cm, or -1 if it returned bad data, or the serial read timed out.

It works like this:

  1. Keep reading until we receive a 0xFF which is the start byte.
  2. Now read the most significant byte (msb).
  3. Read the least significant byte (lsb).
  4. Read the checksum.
  5. Calculate the checksum and compare to the one sent from the device.
  6. If checksum matches, it’s a good reading and so return it. If not, return -1.

It makes no attempt to decide whether the sensor has actually sent a meaningful result, just that what we received matched what it sent. More of validating the results in a later article.

Here is the code in full:

 

/*
 Reads a DYP-ME007Y TX ultrasonic sensor and writes the distance to serial.
 This is the SERIAL VERSION of the sensor
*/

#include <SoftwareSerial.h>

// pin assignments. TX on the Arduino connects to RX on the sensor, RX to TX.
#define TX_PIN D3
#define RX_PIN D4

SoftwareSerial DYPSensor = SoftwareSerial(RX_PIN, TX_PIN);

const int MAX_TRY_SERIAL = 50; // how many cycles of 10ms to wait for before giving up on the sensor (up to 255)

void setup() {

Serial.begin(19200);
 delay(10);

 DYPSensor.begin (9600);

} // end of setup


//
// Reads bytes from RX port and returns a reading in cm

int GetDistance() {
 byte msb, lsb, checksum, checkcalc, tries = 0;
 int distance;

// we want a 255 which is the start of the reading (not msb but saving a byte of variable storage)..
 while (msb != 255) {
 // wait for serial..
 while ( not DYPSensor.available() && tries < MAX_TRY_SERIAL ) {
 delay(10);
 tries++;
 }
 if (tries == MAX_TRY_SERIAL) {
 Serial.println(" TIMED OUT WAITING FOR SERIAL.");
 return -1;
 }
 msb = DYPSensor.read();
 }

// now we collect MSB, LSB, Checksum..
 while ( not DYPSensor.available() ) {
 delay(10);
 }
 msb = DYPSensor.read();

while ( not DYPSensor.available() ) {
 delay(10);
 }
 lsb = DYPSensor.read();

while ( not DYPSensor.available() ) {
 delay(10);
 }
 checksum = DYPSensor.read();

// is the checksum ok?
 checkcalc = 255 + msb + lsb;

if (checksum == checkcalc) {
 distance = msb * 256 + lsb;
 // Round from mm to cm
 distance += 5;
 distance = distance / 10;

return distance;
 } else {
 Serial.println("bad checksum - ignoring reading.");
 return -1;
 }

} // end of GetDistance()



void loop() {

int current_reading;
 current_reading = GetDistance();

Serial.print(current_reading);
 Serial.println("cm");

delay(50);
}