PMS5003 Checksum Errors

Hello, I am using this code and receiving checksum errors. Does anyone know why? Thanks.

// On Leonardo/Micro or others with hardware serial, use those!
// uncomment this line:
// #define pmsSerial Serial1

#include <PMS.h>

// For UNO and others without hardware serial, we must use software serial…
// pin #2 is IN from sensor (TX pin on sensor), leave pin #3 disconnected
// comment these two lines if using hardware serial
#include <SoftwareSerial.h>
SoftwareSerial pmsSerial(2, 3);

void setup() {
// our debugging output
Serial.begin(9600);

// sensor baud rate is 9600
pmsSerial.begin(9600);
}

struct pms5003data {
uint16_t framelen;
uint16_t pm10_standard, pm25_standard, pm100_standard;
uint16_t pm10_env, pm25_env, pm100_env;
uint16_t particles_03um, particles_05um, particles_10um, particles_25um, particles_50um, particles_100um;
uint16_t unused;
uint16_t checksum;
};

struct pms5003data data;

void loop() {
if (readPMSdata(&pmsSerial)) {
// reading data was successful!
Serial.println();
Serial.println("---------------------------------------");
Serial.println(“Concentration Units (standard)”);
Serial.print(“PM 1.0: “); Serial.print(data.pm10_standard);
Serial.print(”\t\tPM 2.5: “); Serial.print(data.pm25_standard);
Serial.print(”\t\tPM 10: “); Serial.println(data.pm100_standard);
Serial.println(”---------------------------------------”);
Serial.println(“Concentration Units (environmental)”);
Serial.print(“PM 1.0: “); Serial.print(data.pm10_env);
Serial.print(”\t\tPM 2.5: “); Serial.print(data.pm25_env);
Serial.print(”\t\tPM 10: “); Serial.println(data.pm100_env);
Serial.println(”---------------------------------------”);
Serial.print(“Particles > 0.3um / 0.1L air:”); Serial.println(data.particles_03um);
Serial.print(“Particles > 0.5um / 0.1L air:”); Serial.println(data.particles_05um);
Serial.print(“Particles > 1.0um / 0.1L air:”); Serial.println(data.particles_10um);
Serial.print(“Particles > 2.5um / 0.1L air:”); Serial.println(data.particles_25um);
Serial.print(“Particles > 5.0um / 0.1L air:”); Serial.println(data.particles_50um);
Serial.print(“Particles > 10.0 um / 0.1L air:”); Serial.println(data.particles_100um);
Serial.println("---------------------------------------");
}
}

boolean readPMSdata(Stream *s) {
if (! s->available()) {
return false;
}

// Read a byte at a time until we get to the special ‘0x42’ start-byte
if (s->peek() != 0x42) {
s->read();
return false;
}

// Now read all 32 bytes
if (s->available() < 32) {
return false;
}

uint8_t buffer[32];
uint16_t sum = 0;
s->readBytes(buffer, 32);

// get checksum ready
for (uint8_t i=0; i<30; i++) {
sum += buffer*;*

  • }*
    _ /* debugging_
  • for (uint8_t i=2; i<32; i++) {*
    _ Serial.print(“0x”); Serial.print(buffer*, HEX); Serial.print(", ");_
    _
    }_
    _
    Serial.println();*_
    _ */_

* // The data comes in endian’d, this solves it so it works on all platforms*
* uint16_t buffer_u16[15];
for (uint8_t i=0; i<15; i++) {
buffer_u16 _= buffer[2 + i2 + 1];
buffer_u16 += (buffer[2 + i*2] << 8);
* }
// put it into a nice struct :slight_smile:
memcpy((void *)&data, (void *)buffer_u16, 30);
if (sum != data.checksum) {
Serial.println(“Checksum failure”);
return false;
}
// success!
return true;
}*_

this looks like its only summing the address of the buffer, not each element (e.g. buffer
```

  • // get checksum ready
    for (uint8_t i=0; i<30; i++) {
      sum += buffer;
    }*
    ```
    is the checksum the sum of each byte or each 16-bit word?