Slim Node Si7021 sensor example

  • @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

  • 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

  • Hardware Contributor

    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.

  • @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?

  • Hardware Contributor

    @rsachoc The "very little clue" is a good reason to play around and learn some. ๐Ÿ˜ƒ
    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.

  • 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.

  • Hardware Contributor

    @rollercontainer Thanks! You're absolutely right. I feel rather stupid not thinking of this. ๐Ÿ˜ž

    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.

  • 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.

  • Some pictures anyway!

    alt text

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    alt text

    alt text

  • Hardware Contributor

    @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:

  • @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?

  • Hardware Contributor

    @rsachoc It's probably it. And yes, it's rigth there. Make sure all of the three small pads interconnect.

  • @m26872 thanks! No time tonight, but a job for testing tomorrow.

  • You could also use the 328 pullups! I had an unwilling Chinese light sensor (MAX44099) that drew a lot of power either with the VCC on or off. Since it's battery powered that is undesireable.

    I used digitalWrite(SDA, LOW); digitalWrite(SCL, LOW); to tie the bus to ground. When the sensor wakes up, it writes HIGH to those pins and the bus is back online. Used a 500ms wait after this to let the sensors stabilise.

    That sensor is now on a 6ยตA sleep current and a average 128ยตA over 2 hours measured with a 2 minute sleep cycle.

  • Tried it this evening, still no luck, let me see what I can get up to over the weekend.

  • Hardware Contributor

    @DavidZH True, internal pull-ups (20k?) should probably be enough for the normal i2c use (short wires, low speed, etc). But I wonder if pull-ups are consuming any significant power during passive state like sleeping sensor. Of course it's a good solution in case there're issues preventing the bus from beeing silent. Or worse, pulled down continuously.
    What was your current before the change?
    I think 500ms awake is a lot.

  • Hardware Contributor

    @rsachoc Crap. Maybe it's something else then.๐Ÿ˜ž

  • I switch them off with a LOW write before the sensor goes to sleep and you're absolutely right about the wait time being very long. In this case I didn't mind because the sensor is powered by a solar panel.
    I can't really remember what the exact value but it was an order of magnitude... I also used the voltage divider way to measure voltage because the Moteino has a regulator on board, so that upped the sleep current a little (10M resistor to keep the current low).

    I went searching because the current went UP when I switched the power to the sensor off before sleep. is a very useful source, but I can't remember where I dug this hack up.
    I will be making other battery sensors for inside with a HTU21d and I will post more on those in a 'My Project' mega gallery including measurements. (And dig around in the HTU datasheet for the start up time....)

  • According to the datasheet the absolute maximum time to get ready is 80ms.

  • Thanx! Saves me a trip! ๐Ÿ˜

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