Web Enabled Temperature and Humidity Using Spark Core

I posted a while ago about the kick starter I backed the Spark Core. I finally got around to making it useful.  Stick with me this is a long post.

The Problem:

Over the last few months one of my filament spools kersploded

20140607_104703Turns out that humidity causes PLA to become brittle and break apart like this especially when its on a small diameter spool.  I always new that PLA was susceptible to humidity but I generally ignored it so I guess I deserve this.  Now based on a suggestion on how better to store my PLA. https://groups.google.com/d/topic/makerbot/Rdx2ZnJeQzs/discussion

long story short I am now using this http://www.westmarine.com/buy/iris-usa-inc–62-8-qt-water-tight-storage-box-clear–14018642

20140706_114102I also put two of these in the box http://amzn.com/B000H0XFCS 

20140706_114125And to monitor the humidity levels one of these http://amzn.com/B0013BKDO8 20140706_114113

Not bad.  The box started out at a startling 45% humidity and quickly dropped to 20-22%.  Since I was monitoring the levels manually I though why not make a wireless sensor to monitor the levels auto-magically.

The Solution

This brings me back to my spark core I mentioned earlier. I went bought one of these https://www.sparkfun.com/products/10167dht22

For the sensing part and quickly and easily plopped it on a breadboard. 20140706_113030I connected this to a 10 ah battery I have to make it wireless. 20140706_113015Then uploaded some code.

// This #include statement was automatically added by the Spark IDE.
#include "idDHT22/idDHT22.h"
#include ;

// declaration for DHT11 handler
int idDHT22pin = D4; //Digital pin for comunications
void dht22_wrapper(); // must be declared before the lib initialization

// DHT instantiate
idDHT22 DHT22(idDHT22pin, dht22_wrapper);

char message[50];
double Humidity =0;
double degF = 0;
double degC = 0;
double DewPoint = 0;
double DewPointSlow = 0;
int result;
int led = 0;
void setup()

	pinMode(led, OUTPUT);
	Spark.variable("message", &message, STRING);
	Spark.variable("Humidity", &Humidity, DOUBLE);
	Spark.variable("degF", &degF, DOUBLE);
	Spark.variable("degC", &degC, DOUBLE);
	Spark.variable("DewPoint", &DewPoint, DOUBLE);
	Spark.variable("DewPointSlow", &DewPointSlow, DOUBLE);
// This wrapper is in charge of calling
// mus be defined like this for the lib work
void dht22_wrapper() {
void loop()

	digitalWrite(led, HIGH);   // turn the LED on (HIGH is the voltage level)

	while (DHT22.acquiring());
	result = DHT22.getStatus();
	switch (result)
			//Serial.println("Error\n\r\tChecksum error");
			//Serial.println("Error\n\r\tISR Time out error");
			//Serial.println("Error\n\r\tResponse time out error");
			//Serial.println("Error\n\r\tData time out error");
			//Serial.println("Error\n\r\tDelta time to small");
			//Serial.println("Error\n\r\tNot started");
			//Serial.println("Unknown error");
    Humidity = DHT22.getHumidity();
    degF = DHT22.getFahrenheit();
    degC = DHT22.getCelsius();
    DewPoint = DHT22.getDewPoint();
    DewPointSlow = DHT22.getDewPointSlow();
    sprintf(message, "{\"Humidity\":%f,\"degF\":%f,\"degC\":%f,\"DewPoint\":%f,\"DewPointSlow\":%f}", Humidity, degF,degC,DewPoint,DewPointSlow);
     digitalWrite(led, LOW);    // turn the LED off by making the voltage LOW

Ok great now to get the data.  This is where the Spark Core is cool. The Spark.variable makes that var available via the web api.

Very cool.  Now to the logging part.

Initially I tried using google docs per this post https://community.spark.io/t/example-logging-and-graphing-data-from-your-spark-core-using-google/2929 but I was having problems.  I will continue to make this work as I like the idea of making the data available anywhere.

In the mean time I setup my pc to log the data using powershell

#put you id and access token in the url string
$url = "https://api.spark.io/v1/devices/xxxx Core ID xxxxxx/message?access_token=xxxx Access Token xxxxx"


    # First we create the request.
    $HTTP_Request = [System.Net.WebRequest]::Create($url)

    # We then get a response from the site.
    $HTTP_Response = $HTTP_Request.GetResponse()

    # We then get the HTTP code as an integer.
    $HTTP_Status = [int]$HTTP_Response.StatusCode

    If ($HTTP_Status -eq 200) { 
        Write-Host "Site is OK!" 
    Else {
        Write-Host "The Site may be down, please check!"

    $requestStream = $HTTP_Response.GetResponseStream()
    $readStream = new-object System.IO.StreamReader $requestStream
    $wrs = $readStream.ReadToEnd()

    $data = $wrs|ConvertFrom-Json

    $data = ((($data.result.Split(",")).replace("}","")).replace("{","")).split(":")

    $Humidity = $data[1]
    $degF = $data[3]
    $degC = $data[5]
    $DewPoint = $data[7]
    $DewPointSlow = $data[9]

    $object = New-Object –TypeName PSObject
    $object | Add-Member –MemberType NoteProperty –Name date –Value (Get-Date)
    $object | Add-Member –MemberType NoteProperty –Name Humidity –Value $Humidity
    $object | Add-Member –MemberType NoteProperty –Name degF –Value $degF
    $object | Add-Member –MemberType NoteProperty –Name degC –Value $degC
    $object | Add-Member –MemberType NoteProperty –Name DewPoint –Value $DewPoint
    $object | Add-Member –MemberType NoteProperty –Name DewPointSlowC –Value $DewPointSlow

    $object |Export-Csv "C:\TempatureData.csv" -Append

    # Finally, we clean up the http request by closing it.

    Start-Sleep -Seconds 600

This code logs the date and the data into a csv.

date Humidity degF degC DewPoint DewPointSlowC
7/6/2014 11:48 38.700001 73.4 23 8.177205 8.207732
7/6/2014 11:58 38.700001 73.4 23 8.177205 8.207732
7/6/2014 12:08 39.599998 73.76 23.2 8.694606 8.725507
7/6/2014 12:18 39 73.76 23.2 8.469035 8.499937
7/6/2014 12:28 38.599998 74.3 23.5 8.583681 8.615134
7/6/2014 12:38 38.599998 73.76 23.2 8.31695 8.347849
7/6/2014 12:48 37.5 73.76 23.2 7.89145 7.922324
7/6/2014 12:58 31.299999 73.58 23.1 5.177949 5.207903

Now I just need to place this in the box and I can remotely monitor and log the conditions in my filament storage box.20140706_124116

Build of Materials

Item Location Price
Spark Core /u.fl connector https://www.spark.io/ $39
2.4GHz Antenna – Adhesive (U.FL connector) https://www.sparkfun.com/products/11320 $4.95
Humidity and Temperature Sensor – RHT03 https://www.sparkfun.com/products/10167 $9.95
Breadboard – Self-Adhesive (White) https://www.sparkfun.com/products/12002 $4.95
10k ohm resistor
small led (optional)
470 ohm resistor (optional)
Jumper wires

There you have it.  This is just a quick and dirty solution.  I am sure it can be done cheaper and easier.  This was done with the items I already had on hand with the exception of the DHT22.

4 thoughts on “Web Enabled Temperature and Humidity Using Spark Core

    • I have seen my core in a flipped out state (technical term) but I don’t think it was in the disconnected cloud state according to the doc (http://docs.spark.io/) it would be flashing red in some interval. What I have seen is that in my code I flash a led when I am reading from the sensor and I have seen the led constantly lit which should not happen. I have not done any troubleshooting to quantify the problem and it’s only happened 3 times I can remember. I have simply pushed the reset on the core and it started working as it should.

    • Yeah, I’ve seen this as well, it’s pretty frustrating – I’ll come back and it’ll just be flashing green. Did you ever find the cause of this?

      My initial thought was a memory issue, but there are a couple places in the code that perhaps should be fixed (max retry and abort on the while(DHT22.acquiring()), for example, and the fact that delay is blocking and causes it to ignore interrupts, which the core perhaps depends on to maintain connectivity.

      Any thoughts?

      • I have not tackled this issue yet (but it is starting to get on my nerves). I am also leaning towards a memory issue but, you are right. My code is quite terrible with the while(DHT22.acquiring()) potential infinite loop. Kind of funny that I would find this unacceptable programming practice at work but I am using it here. I was thinking about adding some leds and turning them high at various parts of the script to pin point where the issue is occurring (good ol physical debugging).

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