[SOLVED] s17021 vs HTU21

[4994james]

I have had plenty of success with s17021 sensors and the mysensors library in the past however I have recently purchased some more boards for what I thought was a reasonable deal from Amazon. This is exactly what I have.

The issue I have is that none of them work. When it gets to Begin() it just stops. It doesn't return at all so doesn't issue a "sensor not detected" which is what I would expect if not connected. I hooked up my logic analyser trace and can see the initial command but nothing comes back.
I can see the basic chip is different to the ones to the boards I have used previously so assume there is some software incompatibility. However I have looked at the data sheet and it is a I2C component and seems to have identical addresses and commands as the si7021. Have I just got a load of defective items or should I be using different software?

[mfalkvidd]

Maybe try an i2c scanner to see if the datasheet has got the address wrong? https://playground.arduino.cc/Main/I2cScanner/

[Yveaux]

@4994james How do you connect the board? Do you have the I2C pull-up resistors mounted?

[4994james]

@mfalkvidd Hi. Thank you. Most useful. Just tried and it reports:

I2C Scanner
Scanning...
I2C device found at address 0x40 !
done

So seems to be the same as si7021 and correct. Will respond to @Yveaux with more details as still not working with si7021 library.

[4994james]

@Yveaux
Many thanks for your response.
I think the board has onboard pull up resistors, But to eliminate doubt I added 2 1k pull ups to sda and scl. This is the debug output when i use a sparkfun si7021 board (also with same pull ups - though not needed for this board for sure):

setup!10446 MCO:BGN:INIT OK,TSP=1
Temp 18.83C	Hum 50.94

and this is a screenshot of the trace on sda and scl:

E3 is temp command.

followed by

Temp reading and another (not shown) set of commands and humidity reading.

However with the HTU21D the sketch hangs here:

setup!10397 MCO:BGN:INIT OK,TSP=1

i get the same first command trace as you would expect (same library) but no response from the board.

[Yveaux]

@4994james as you own the tools to monitor the i2c traffic, what is going on with the htu on the bus during initialization?

[4994james]

@Yveaux
This is what I see on trigger. this is identical when HTU21 and Si7021 boards are connected.

[4994james]

@4994james
Hi. I have been reading https://forum.mysensors.org/topic/476/htu21d-humidity-temperature-sensor/8 and have now got this working using the adafruit htu21d library. Not sure what the difference is but there obviously is something. I also confirm that the board works without external pull up resistors. Thanks for you help.

This is my new (working) code:

/**
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 *******************************
 *
 * REVISION HISTORY
 * Version 1.0: Andrew Sutcliffe
 *  
 * DESCRIPTION
 * This sketch provides an example of how to implement a humidity/temperature
 * sensor using a HTU21DF Sensor.
 *  
 * For more information, please visit:
 * http://www.mysensors.org/build/humidity
 * 
 * Connect Vin to 3-5VDC
 * Connect GND to ground
 * Connect SCL to I2C clock pin (A5 on UNO)
 * Connect SDA to I2C data pin (A4 on UNO)
 * 
 */

// Enable debug prints
#define MY_DEBUG

// Enable and select radio type attached 
//#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69
#define MY_RS485

// Define this to enables DE-pin management on defined pin
#define MY_RS485_DE_PIN 2

// Set RS485 baud rate to use
#define MY_RS485_BAUD_RATE 9600

#include <MySensors.h>  
#include <Wire.h>
#include "Adafruit_HTU21DF.h"

Adafruit_HTU21DF htu = Adafruit_HTU21DF();

// Set this offset if the sensor has a permanent small offset to the real temperatures
#define SENSOR_TEMP_OFFSET 0

// Sleep time between sensor updates (in milliseconds)

static const uint64_t UPDATE_INTERVAL = 60000;

// Force sending an update of the temperature after n sensor reads, so a controller showing the
// timestamp of the last update doesn't show something like 3 hours in the unlikely case, that
// the value didn't change since;
// i.e. the sensor would force sending an update every UPDATE_INTERVAL*FORCE_UPDATE_N_READS [ms]
static const uint8_t FORCE_UPDATE_N_READS = 10;

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1

#define MY_NODE_ID 104

float lastTemp;
float lastHum;
uint8_t nNoUpdatesTemp;
uint8_t nNoUpdatesHum;
bool metric = true;

MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);

void presentation()  
{ 
  // Send the sketch version information to the gateway
  sendSketchInfo("HTU21DF-TemperatureAndHumidity", "1.0");

  // Register all sensors to gw (they will be created as child devices)
  present(CHILD_ID_HUM, S_HUM);
  present(CHILD_ID_TEMP, S_TEMP);
}

void setup()
{
  Serial.begin(115200);
  Serial.println("HTU21D-F test");

  if (!htu.begin()) {
    Serial.println("Couldn't find sensor!");
    while (1);
    }
}

void loop(){
  // Get temperature from HTU21DF library
  float temperature = (htu.readTemperature());
 if (temperature != lastTemp || nNoUpdatesTemp == FORCE_UPDATE_N_READS) {
    // Only send temperature if it changed since the last measurement or if we didn't send an update for n times
    lastTemp = temperature;
    
    // Reset no updates counter
    nNoUpdatesTemp = 0;
    temperature += SENSOR_TEMP_OFFSET;
    send(msgTemp.set(temperature, 1));

    #ifdef MY_DEBUG
    Serial.print("T: ");
    Serial.println(temperature);
    #endif
  } 
  else {
    // Increase no update counter if the temperature stayed the same
    nNoUpdatesTemp++;
  }

  // Get humidity from HTU21DF library
  float humidity = (htu.readHumidity());
  if (humidity != lastHum || nNoUpdatesHum == FORCE_UPDATE_N_READS) {
    // Only send humidity if it changed since the last measurement or if we didn't send an update for n times
    lastHum = humidity;
    // Reset no updates counter
    nNoUpdatesHum = 0;
    send(msgHum.set(humidity, 1));

    #ifdef MY_DEBUG
    Serial.print("H: ");
    Serial.println(humidity);
    #endif
}
  else {
    // Increase no update counter if the humidity stayed the same
    nNoUpdatesHum++;
  }

  // Sleep for a while to save energy
  sleep(UPDATE_INTERVAL); 
}

[Yveaux]

@4994james great to hear you solved it, and thanks for reporting back!