Slim Node Si7021 sensor example

[rsachoc]

Ok so that may be the problem then! Let me solder it the right way and see if that helps otherwise I'm going to create a bare bones slim mode as suggested

edit to confirm the positive leg of the capacitor goes to the positive marked plus sign hole on the board?

[rsachoc]

OK so I changed the polarity of the 4.7uf capacitor and I'm still receiving the same error. So I built a barebones one without sensor and without NRF. I am still getting the same error when uploading the sketch via the FTDI adaptor. I tried uploading a sketch to a Sensebender I have and it worked fine, so that rules out the FTDI adaptor.

Some pics in case someone can spot something obvious.

http://i.imgur.com/1SV0qO2.jpg

http://i.imgur.com/mUp87hB.jpg

http://i.imgur.com/oCqcDpo.jpg

So I can only think that it must be related to the ATMega bootloader? In the how to burn a bootloader thread, I received the following when trying to burn the bootloader, so I assumed it uploaded correctly?

C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/bin/avrdude -CC:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -cstk500v1 -PCOM5 -b19200 -e -Ulock:w:0x3F:m -Uefuse:w:0x05:m -Uhfuse:w:0xDE:m -Ulfuse:w:0xFF:m 

avrdude: Version 6.0.1, compiled on Apr 15 2015 at 19:59:58
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2009 Joerg Wunsch

         System wide configuration file is "C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/etc/avrdude.conf"

         Using Port                    : COM5
         Using Programmer              : stk500v1
         Overriding Baud Rate          : 19200
         AVR Part                      : ATmega328P
         Chip Erase delay              : 9000 us
         PAGEL                         : PD7
         BS2                           : PC2
         RESET disposition             : dedicated
         RETRY pulse                   : SCK
         serial program mode           : yes
         parallel program mode         : yes
         Timeout                       : 200
         StabDelay                     : 100
         CmdexeDelay                   : 25
         SyncLoops                     : 32
         ByteDelay                     : 0
         PollIndex                     : 3
         PollValue                     : 0x53
         Memory Detail                 :

                                  Block Poll               Page                       Polled
           Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW  MaxW   ReadBack
           ----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
           eeprom        65    20     4    0 no       1024    4      0  3600  3600 0xff 0xff
           flash         65     6   128    0 yes     32768  128    256  4500  4500 0xff 0xff
           lfuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           hfuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           efuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           lock           0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           calibration    0     0     0    0 no          1    0      0     0     0 0x00 0x00
           signature      0     0     0    0 no          3    0      0     0     0 0x00 0x00

         Programmer Type : STK500
         Description     : Atmel STK500 Version 1.x firmware
         Hardware Version: 2
         Firmware Version: 1.18
         Topcard         : Unknown
         Vtarget         : 0.0 V
         Varef           : 0.0 V
         Oscillator      : Off
         SCK period      : 0.1 us

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.02s

avrdude: Device signature = 0x1e950f
avrdude: erasing chip
avrdude: reading input file "0x3F"
avrdude: writing lock (1 bytes):

Writing | ################################################## | 100% 0.01s

avrdude: 1 bytes of lock written
avrdude: verifying lock memory against 0x3F:
avrdude: load data lock data from input file 0x3F:
avrdude: input file 0x3F contains 1 bytes
avrdude: reading on-chip lock data:

C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/bin/avrdude -CC:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -cstk500v1 -PCOM5 -b19200 -Uflash:w:C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\arduino\avr/bootloaders/optiboot/optiboot_atmega328.hex:i -Ulock:w:0x0F:m 
Reading | ################################################## | 100% 0.01s

avrdude: verifying ...
avrdude: 1 bytes of lock verified
avrdude: reading input file "0x05"
avrdude: writing efuse (1 bytes):

Writing | ################################################## | 100% 0.01s

avrdude: 1 bytes of efuse written
avrdude: verifying efuse memory against 0x05:
avrdude: load data efuse data from input file 0x05:
avrdude: input file 0x05 contains 1 bytes
avrdude: reading on-chip efuse data:

Reading | ################################################## | 100% 0.01s

avrdude: verifying ...
avrdude: 1 bytes of efuse verified
avrdude: reading input file "0xDE"
avrdude: writing hfuse (1 bytes):

Writing | ################################################## | 100% 0.01s

avrdude: 1 bytes of hfuse written
avrdude: verifying hfuse memory against 0xDE:
avrdude: load data hfuse data from input file 0xDE:
avrdude: input file 0xDE contains 1 bytes
avrdude: reading on-chip hfuse data:

Reading | ################################################## | 100% 0.01s

avrdude: verifying ...
avrdude: 1 bytes of hfuse verified
avrdude: reading input file "0xFF"
avrdude: writing lfuse (1 bytes):

Writing | ################################################## | 100% 0.01s

avrdude: 1 bytes of lfuse written
avrdude: verifying lfuse memory against 0xFF:
avrdude: load data lfuse data from input file 0xFF:
avrdude: input file 0xFF contains 1 bytes
avrdude: reading on-chip lfuse data:

Reading | ################################################## | 100% 0.01s

avrdude: verifying ...
avrdude: 1 bytes of lfuse verified

avrdude done.  Thank you.


avrdude: Version 6.0.1, compiled on Apr 15 2015 at 19:59:58
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2009 Joerg Wunsch

         System wide configuration file is "C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\tools\avr/etc/avrdude.conf"

         Using Port                    : COM5
         Using Programmer              : stk500v1
         Overriding Baud Rate          : 19200
         AVR Part                      : ATmega328P
         Chip Erase delay              : 9000 us
         PAGEL                         : PD7
         BS2                           : PC2
         RESET disposition             : dedicated
         RETRY pulse                   : SCK
         serial program mode           : yes
         parallel program mode         : yes
         Timeout                       : 200
         StabDelay                     : 100
         CmdexeDelay                   : 25
         SyncLoops                     : 32
         ByteDelay                     : 0
         PollIndex                     : 3
         PollValue                     : 0x53
         Memory Detail                 :

                                  Block Poll               Page                       Polled
           Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW  MaxW   ReadBack
           ----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
           eeprom        65    20     4    0 no       1024    4      0  3600  3600 0xff 0xff
           flash         65     6   128    0 yes     32768  128    256  4500  4500 0xff 0xff
           lfuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           hfuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           efuse          0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           lock           0     0     0    0 no          1    0      0  4500  4500 0x00 0x00
           calibration    0     0     0    0 no          1    0      0     0     0 0x00 0x00
           signature      0     0     0    0 no          3    0      0     0     0 0x00 0x00

         Programmer Type : STK500
         Description     : Atmel STK500 Version 1.x firmware
         Hardware Version: 2
         Firmware Version: 1.18
         Topcard         : Unknown
         Vtarget         : 0.0 V
         Varef           : 0.0 V
         Oscillator      : Off
         SCK period      : 0.1 us

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.02s

avrdude: Device signature = 0x1e950f
avrdude: NOTE: "flash" memory has been specified, an erase cycle will be performed
         To disable this feature, specify the -D option.
avrdude: erasing chip
avrdude: reading input file "C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\arduino\avr/bootloaders/optiboot/optiboot_atmega328.hex"
avrdude: writing flash (32768 bytes):

Writing | ################################################## | 100% 0.00s

avrdude: 32768 bytes of flash written
avrdude: verifying flash memory against C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\arduino\avr/bootloaders/optiboot/optiboot_atmega328.hex:
avrdude: load data flash data from input file C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\arduino\avr/bootloaders/optiboot/optiboot_atmega328.hex:
avrdude: input file C:\Users\James\Desktop\RPi Openhab\arduino-1.6.7-windows\hardware\arduino\avr/bootloaders/optiboot/optiboot_atmega328.hex contains 32768 bytes
avrdude: reading on-chip flash data:

Reading | ################################################## | 100% -0.00s

avrdude: verifying ...
avrdude: 32768 bytes of flash verified
avrdude: reading input file "0x0F"
avrdude: writing lock (1 bytes):

Writing | ################################################## | 100% 0.02s

avrdude: 1 bytes of lock written
avrdude: verifying lock memory against 0x0F:
avrdude: load data lock data from input file 0x0F:
avrdude: input file 0x0F contains 1 bytes
avrdude: reading on-chip lock data:

Reading | ################################################## | 100% 0.01s

avrdude: verifying ...
avrdude: 1 bytes of lock verified

avrdude done.  Thank you.

[m26872]

@rsachoc Looks like you're missing the R1 resistor?

[rsachoc]

@m26872 well that is probably it! I didn't even realise I needed that, oops! Sorry :disappointed: ! Let me try and get one (I think I have some already) and get soldering

[rsachoc]

It lives! Well the one node I created does at least! I'll troubleshoot it, but the problem was the R1 resistor, which I (noobishly) forgot about! But very pleased, and thanks to m26872 especially and everyone else who helped.

I've updated the lessons learn post too!

[rsachoc]

I just received my non-3.3v Si7021, and have now updated the lessons learnt post, as this board is tiny and I managed to mess up the soldering completely. Ordered the 3.3 ready version now, another month wait...

[siod]

@carlierd said:

@ar91 Please find the code I used in 3 different nodes. The good thing with the playground lib is that there is error message if dialog with DHT22 failed.

/**
 * 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.
 *
 */

/**************************************************************************************/
/* Temperature, humidity and luminosity measurements.                                 */
/*                                                                                    */
/* Version     : 1.1.6                                                                */
/* Date        : 10/01/2016                                                           */
/* Modified by : David Carlier                                                        */
/**************************************************************************************/
/*                                ---------------                                     */
/*                            RST |             |  A5                                 */
/*                            RX  |             |  A4                                 */
/*                            TX  |   ARDUINO   |  A3                                 */
/*     RFM69 (DIO0) --------- D2  |     UNO     |  A2                                 */
/*            DHT22 --------- D3  |             |  A1                                 */
/*            Power --------- D4  | ATMEGA 328p |  A0 --------- Light dep. resistor   */
/*              +3v --------- VCC |             | GND --------- GND                   */
/*              GND --------- GND |  8MHz int.  | REF                                 */
/*                            OSC |             | VCC --------- +3v                   */
/*                            OSC |             | D13 --------- RFM69 (SCK)           */
/*                            D5  |             | D12 --------- RFM69 (MISO)          */
/*                            D6  |             | D11 --------- RFM69 (MOSI)          */
/*                            D7  |             | D10 --------- RFM69 (NSS)           */
/*                            D8  |             |  D9                                 */
/*                                ---------------                                     */
/*                                                                                    */
/* Power = Vcc for LDR.                                                               */
/* +3v = 2*AA                                                                         */
/*                                                                                    */
/**************************************************************************************/

#include <SPI.h>
#include <MySensor.h>
#include <dht.h>
#include <MyTransportRFM69.h>
#include <MySigningAtsha204Soft.h>

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1
#define CHILD_ID_LIGHT 2
#define CHILD_ID_VOLTAGE 3
#define LIGHT_SENSOR_ANALOG_PIN 0
#define HUMIDITY_SENSOR_DIGITAL_PIN 3
#define POWER_PIN 4
//unsigned long SLEEP_TIME = 850000; // Sleep time between reads (in milliseconds) (close to 15')
unsigned long SLEEP_TIME = 275000; // Sleep time between reads (in milliseconds) (close to 5')

//Construct MySensors library
MySigningAtsha204Soft signer;
MyHwATMega328 hw;
MyTransportRFM69 transport;
MySensor gw(transport, hw, signer);
dht DHT;
MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
MyMessage msgLum(CHILD_ID_LIGHT, V_LEVEL);
MyMessage msgVolt(CHILD_ID_VOLTAGE, V_VOLTAGE);

/**************************************************************************************/
/* Initialization                                                                     */
/**************************************************************************************/
void setup()
  {
  //Get time (for setup duration)
  #ifdef DEBUG
    unsigned long startTime = millis();
  #endif

  //Start MySensors
  gw.begin();

  //Send the Sketch Version Information to the Gateway
  gw.sendSketchInfo("GHAS sensor", "1.1.5");

  //Register all sensors to gw (they will be created as child devices)
  gw.present(CHILD_ID_HUM, S_HUM);
  gw.present(CHILD_ID_TEMP, S_TEMP);
  gw.present(CHILD_ID_LIGHT, S_LIGHT_LEVEL);
  gw.present(CHILD_ID_VOLTAGE, S_MULTIMETER);

  //Delay for DHT22
  delay(1500);

  //Print setup debug
  #ifdef DEBUG
    int duration = millis() - startTime;
    Serial.print("[Setup duration: "); Serial.print(duration, DEC); Serial.println(" ms]");
  #endif
  }

/**************************************************************************************/
/* Main loop                                                                          */
/**************************************************************************************/
void loop()
  {
  //Get time (for a complete loop)
  #ifdef DEBUG
    unsigned long startTime = millis();
  #endif

  //Power on
  powerOnPeripherals();

  //Get DHT22 data
  int dht22Result = DHT.read22(HUMIDITY_SENSOR_DIGITAL_PIN);
  switch (dht22Result)
    {
    case DHTLIB_OK:  
                //Serial.println("OK,\t");
                break;
    case DHTLIB_ERROR_CHECKSUM:
                #ifdef DEBUG
                  Serial.println("Checksum error,\t");
                #endif
                break;
    case DHTLIB_ERROR_TIMEOUT:
                #ifdef DEBUG
                  Serial.println("Time out error,\t");
                #endif
                break;
    case DHTLIB_ERROR_CONNECT:
                #ifdef DEBUG
                  Serial.println("Connect error,\t");
                #endif
                break;
    case DHTLIB_ERROR_ACK_L:
                #ifdef DEBUG
                  Serial.println("Ack Low error,\t");
                #endif
                break;
    case DHTLIB_ERROR_ACK_H:
                #ifdef DEBUG
                  Serial.println("Ack High error,\t");
                #endif
                break;
    default:
                #ifdef DEBUG
                  Serial.println("Unknown error,\t");
                #endif
                break;
    }

  //Get temperature and humidity
  float temperature = 0;
  float humidity = 0;
  if (dht22Result == DHTLIB_OK)
    {
    temperature = DHT.temperature;
    humidity = DHT.humidity;
    }

  //Get power before luminosity to use real voltage
  float realVoltage = getVoltage() / 100.0;
  int batteryPcnt = realVoltage * 100 / 3.0;
  if (batteryPcnt > 100) {batteryPcnt = 100;}
  int lux = computeIlluminance(realVoltage);

  //Power off
  powerOffPeripherals();

  //Send data to gateway
  gw.send(msgHum.set(humidity, 1));
  gw.send(msgTemp.set(temperature, 1));
  gw.send(msgLum.set(lux));
  gw.send(msgVolt.set(realVoltage, 2));
  gw.sendBatteryLevel(batteryPcnt);

  //Print debug
  #ifdef DEBUG
    Serial.print(temperature, 1);
    Serial.print(" degC");
    Serial.print("   ");
    Serial.print(humidity, 1);
    Serial.print(" %");
    Serial.print("   ");
    Serial.print(lux);
    Serial.print(" lx");
    Serial.print("   ");
    Serial.print(realVoltage);
    Serial.print(" v");
    int duration = millis() - startTime;
    Serial.print("   ");
    Serial.print("["); Serial.print(duration, DEC); Serial.println(" ms]");
    Serial.flush();
  #endif

  //Sleep
  gw.sleep(SLEEP_TIME);
  }

/**************************************************************************************/
/* Allows to compute illuminance (in LUX) from LIGHT_SENSOR_ANALOG_PIN.               */
/**************************************************************************************/
int computeIlluminance(float realVoltage)
  {
  //Get luminosity
  int luminosity = analogRead(LIGHT_SENSOR_ANALOG_PIN);
  //Calculating the voltage in the input of the ADC
  double voltage = realVoltage * ((double)luminosity / 1024.0);
  //Calculating the resistance of the photoresistor in the voltage divider
  double resistance = (10.0 * realVoltage) / voltage - 10.0;
  //Calculating the intensity of light in lux and return it
  int illuminance = 255.84 * pow(resistance, -10/9);
  return illuminance;
  }

/**************************************************************************************/
/* Allows to get the real Vcc (return value * 100).                                   */
/**************************************************************************************/
int getVoltage()
  {
  const long InternalReferenceVoltage = 1056L;
  ADMUX = (0<<REFS1) | (1<<REFS0) | (0<<ADLAR) | (1<<MUX3) | (1<<MUX2) | (1<<MUX1) | (0<<MUX0);
  delay(50);  // Let mux settle a little to get a more stable A/D conversion
  //Start a conversion  
  ADCSRA |= _BV( ADSC );
  //Wait for it to complete
  while (((ADCSRA & (1<<ADSC)) != 0));
  //Scale the value
  int result = (((InternalReferenceVoltage * 1023L) / ADC) + 5L) / 10L;
  return result;
  }

/**************************************************************************************/
/* Allows to power ON peripherals.                                                    */
/**************************************************************************************/
void powerOnPeripherals()
  {
  //Power-up
  pinMode (POWER_PIN, OUTPUT);
  digitalWrite (POWER_PIN, HIGH);
  delay(1);
  }

/**************************************************************************************/
/* Allows to power OFF peripherals.                                                   */
/**************************************************************************************/
void powerOffPeripherals()
  {
  //Power off
  digitalWrite (HUMIDITY_SENSOR_DIGITAL_PIN, LOW);
  digitalWrite (POWER_PIN, LOW);
  pinMode (HUMIDITY_SENSOR_DIGITAL_PIN, INPUT);
  pinMode (POWER_PIN, INPUT);
  }

Hope it helps !

David.

So the DHT22 works at 1MHz with 2 AAs and your code you´ve posted? No physical differnces?

[rsachoc]

So I think I've finally got everything up and running! This is what I'm getting at the serial monitor in the IDE:

Serial started
Voltage: 3359 mV
send: 132-132-0-0 s=255,c=3,t=15,pt=2,l=2,sg=0,st=ok:0
send: 132-132-0-0 s=255,c=0,t=17,pt=0,l=5,sg=0,st=ok:1.5.4
send: 132-132-0-0 s=255,c=3,t=6,pt=1,l=1,sg=0,st=ok:0
read: 0-0-132 s=255,c=3,t=15,pt=0,l=2,sg=0:

sensor started, id=132, parent=0, distance=1
send: 132-132-0-0 s=255,c=3,t=11,pt=0,l=15,sg=0,st=ok:EgTmpHumBat5min
send: 132-132-0-0 s=255,c=3,t=12,pt=0,l=10,sg=0,st=ok:1.0 151106
send: 132-132-0-0 s=0,c=0,t=6,pt=0,l=0,sg=0,st=ok:
send: 132-132-0-0 s=1,c=0,t=7,pt=0,l=0,sg=0,st=ok:
Node and 2 children presented.

What I'm trying to figure out is where the temp and humidity reading are so I can get them into MQTT/OpenHab. Looking at the output, I can't see which one is the temp, humidity or battery level?

[m26872]

@rsachoc Is that all you get? Please also set sleep_time to 15000 for debug, if you haven't already done it.

[rsachoc]

@m26872 thanks, I've set that, no change even after more than 15seconds and debug set.

Could it be the way I've connected the si7021? I've got it as follows:

1. A4 to SDA
2. A5 to SCL
3. GND to GND
4. VCC to 3.3v

[rsachoc]

Maybe I need to add that I'm running the 2.0 MQTT controller? Not sure if that makes a difference? GatewayW5100MQTTClient

Just had a look what's going on on the controller side, this is what I see

0;255;3;0;9;Starting gateway (RNNGA-, 2.0.0-beta)
0;255;3;0;9;Radio init successful.
0;255;3;0;9;Init complete, id=0, parent=0, distance=0
0;255;3;0;9;Attempting MQTT connection...
0;255;3;0;9;MQTT connected
0;255;3;0;9;read: 132-132-0 s=255,c=3,t=15,pt=2,l=2,sg=0:0
0;255;3;0;9;send: 0-0-132-132 s=255,c=3,t=15,pt=0,l=2,sg=0,st=ok:

0;255;3;0;9;read: 132-132-0 s=255,c=0,t=17,pt=0,l=5,sg=0:1.5.4
0;255;3;0;9;Sending message on topic: mygateway1-out/132/255/0/0/17
0;255;3;0;9;read: 132-132-0 s=255,c=3,t=6,pt=1,l=1,sg=0:0
0;255;3;0;9;Sending message on topic: mygateway1-out/132/255/3/0/6
0;255;3;0;9;read: 132-132-0 s=255,c=3,t=11,pt=0,l=15,sg=0:EgTmpHumBat5min
0;255;3;0;9;Sending message on topic: mygateway1-out/132/255/3/0/11
0;255;3;0;9;read: 132-132-0 s=255,c=3,t=12,pt=0,l=10,sg=0:1.0 151106
0;255;3;0;9;Sending message on topic: mygateway1-out/132/255/3/0/12
0;255;3;0;9;read: 132-132-0 s=0,c=0,t=6,pt=0,l=0,sg=0:
0;255;3;0;9;Sending message on topic: mygateway1-out/132/0/0/0/6
0;255;3;0;9;read: 132-132-0 s=1,c=0,t=7,pt=0,l=0,sg=0:
0;255;3;0;9;Sending message on topic: mygateway1-out/132/1/0/0/7

[m26872]

@rsachoc
My initial guess would be that you get stuck at this line:

 si7021_env data = humiditySensor.getHumidityAndTemperature();

Did you try your Si7021 on some plain arduino first? Just with some simple example code.

[rsachoc]

@m26872 thanks, yes, I guessed that something might be wrong with the sensor, I checked continuity between the board and the sensor and all seemed fine.

To test on an Arduino, I've honestly very little clue how to do this. Could I utilise the breadboard and Arduino I used to flash the AtMega?

[m26872]

@rsachoc The "very little clue" is a good reason to play around and learn some. :smiley:
You should not use a 5V Uno directly to sensor without voltage regulator and logic level converter. The Si7021 spec is 1.9-3.6V.
If you don't have a Arduino Pro Mini 3.3V, I suppose your best option is the SlimNode you already got. Try it at least at 8MHz (use suitable fuse settings, bootloader and baud rate), of course external crystal if you have.

[rollercontainer]

The most SI7021 coming from ebay are with voltage regulator and level shifter. I searched for a raw version and there are only very few... If you are not sure, post a link or a foto.

[m26872]

@rollercontainer Thanks! You're absolutely right. I feel rather stupid not thinking of this. :(

So @rsachoc, if you're have some GY-21 like boards still not yet modded like described in first post of this thread, then they should work excellent with your Uno.

[rsachoc]

Thanks both, I have the "pre-modded" si7021, so it's the one that should operate at between the 1.9 and 3.3v. I the Arduino I used to burn the Atmega is a knockoff, so it has both 3.3v and 5v. Let me do some research and see if I can test the si7021 using it.

[rsachoc]

Some pictures anyway!

[m26872]

@rsachoc Great with pictures! It looks like you haven't enabled the pull-up resistors by filling the solder jumpers in the middle of the board? Like this: https://cdn.sparkfun.com/assets/3/f/6/5/a/52855764757b7f06478b4567.jpg

[rsachoc]

@m26872 oh! I didn't realise I needed to do that, could that be the problem? Do I just need to fill with solder the bit just below where the DA and "-" is?