IoT NTC Thermistor Temps Using thethings.iO

Wireless NTC Thermistor probes

In this project, we show you how to connect some NTC thermistors to the mcMod120 to create a wireless, ultra-low power, coin-cell powered temperature sensor and then display the incoming real-time information into thethings.iO IoT cloud application!

Potential use-cases?

The mcMod120 already features a TMP102 temperature sensor, but what about when you need to measure liquids, extreme temperatures, specific locations, etc?

• Cold-chain management, Food service, trucking, etc

• Agriculture: livestock trough temps, water storage, commercial greenhouses

• Measure aquariums, ponds, birdbaths, puddles (Imagine, an IoT puddle!), etc

• connect your lasagna to the internet! Literally, you could! :)

• Etc!

How the platform works:

The mcThings platform includes 2 main components: mcModules and mcGateways. A powered and connected mcGateway creates the mcAir network (up to 200m range under optimal conditions) and bridges the information between the mcModules (within range) to and from the Internet. Using the IDE (mcStudio) and mcScript (ultra-low power programming language - a subset of VB.NET) allows you to wirelessly connect, debug and program modules with your customized scripts.

Note - You also require an mcDongle to complete firmware updates on the modules/devices and gateways! We recommend looking at the mcModule120 Dev kit which includes everything you need to get going!!

Attaching the thermistors

We soldered two different NTC thermistors directly to the mcMod120. For the first sensor, we added the resistor to act as the voltage divider and for the second sensor, we used the built-in voltage divider on the module.

PINS used:

Resistor: PIN 0 & PIN 6

Thermistor #1: PIN 0 (to resistor) & GND

Thermistor #2: PIN 7 & GND

*Note - If you are hesitant to solder right away or want to connect other sensors before soldering, mcThings offers the mcDev board that allows you to use breakout pins among other features.

Enclosure

We picked up a little case from a local electronic store and used a step bit to move the connected sensors through the case and then closed it up.

Programming the mcModule120

Using thethings.iO recent walk-through on how to connect mcThings devices to their IoT application (more on this below), we modified the code from Github to send the information from the thermistors to the dashboard.

MAIN Program: Notice that we define the Pins to ensure that we are measuring properly (based on where they were soldered, modifiable based on where you connect the sensor on your module).

Define PinMode Pin0 As AnalogInput Alias USP10972_VOLTAGE 
Define PinMode Pin6 As DigitalOutput Alias USP10972_DIVIDER_ENABLE 
Define PinMode Pin7 As AnalogInputPullUp Alias CWF1B104F3950_VOLTAGE 
Class ThermistorTheThings 
   Shared token As String  
   Shared thethings As thethingsiO 
   'Constants for Thermistor 1 
   Const CWF1B104F3950_BETA As Integer = 3950 
   Const CWF1B104F3950_R25 As Integer = 100000 '100kOhm 
   Const CWF1B104F3950_DIVIDER_R1 As Integer = 100000 '100kOhm 
   'Constants for Thermistor 2 
   Const USP10972_BETA As Integer = 3892 
   Const USP10972_R25 As Integer = 10000 '10kOhm 
   Const USP10972_DIVIDER_R1 As Integer = 10000 '10kOhm 
   Shared CWF1B104F3950 As NTCTermistor 
   Shared USP10972 As NTCTermistor 
   Shared Event Boot() 
       'disable USP10972 voltage divider 
       USP10972_DIVIDER_ENABLE = False 
       'Create new NTC Thermistors with beta and R25 vaules 
       CWF1B104F3950 = New NTCTermistor(CWF1B104F3950_BETA, CWF1B104F3950_R25) 
       USP10972 = New NTCTermistor(USP10972_BETA, USP10972_R25) 
       'Assign token for thethings.io payload 
       token = "YOURTOKENHERE" 
       thethings = New thethingsiO(token) 
   End Event 
   Shared Event measureTemperature() RaiseEvent Every 30 Seconds 
       'Turn on Resistor Divider to enable reading of USP10972 NTC probe 
       USP10972_DIVIDER_ENABLE = True 
       'Turn on OPAMP to enable reading of CWF1B104F3950 NTC probe 
       Device.EnableOpamp() 
       'sleep for 10ms for voltage dividers to stabilize 
       Thread.Sleep(10000) 
       'Get thermistor resistance from resistor dividers 
       Dim thermistorResistance As Float = CWF1B104F3950_DIVIDER_R1 * (1 / ((Device.BatteryVoltage().ToFloat/ CWF1B104F3950_VOLTAGE.ToFloat) - 1)) 
       Dim thermistor2Resistance As Float = USP10972_DIVIDER_R1 * (1 / ((Device.BatteryVoltage().ToFloat/ USP10972_VOLTAGE.ToFloat) - 1)) 
       'turn off voltage divider to conserve power 
       USP10972_DIVIDER_ENABLE = False 
       'turn off opamp to conserve power 
       Device.DisableOpamp() 
       'measure and convert batter voltage to float 
       Dim battShort As Short = Device.BatteryVoltage() 
       Dim battFloat As Float = battShort / 1000 
       'Convert data to string to add to JSON data 
       Dim battString As String = battFloat.ToString() 
       Dim tempTMP102string As String = Temperature.GetTemp().ToString 
       Dim tempstring As String = CWF1B104F3950.TemperatureCFromResistance(thermistorResistance).ToString 
       Dim temp2string As String = USP10972.TemperatureCFromResistance(thermistor2Resistance).ToString 
       'create thethings.io payload and publish 
       Dim tempJson As Json = New Json 
       thethings.addValues("battery", battString) 
       thethings.publish() 
       thethings.addValues("temperature", tempstring) 
       thethings.publish() 
       thethings.addValues("temperature2", temp2string) 
       thethings.publish() 
       thethings.addValues("TMP102temperature", tempTMP102string) 
       thethings.publish() 
   End Event 
End Class

LIBRARIES

There are two libraries for this project, for the NTC sensors and the TMP102 (yes, we also measured the ambient temperature using the built-in temperature sensor)

thethings.io library

Class thethingsiO 
   Private topic As String = "" 
   Private payload As String = "" 
   Private firstValue As Boolean 
   Public Sub New(thingToken As String) 
       topic = thingToken 
   End Sub 
   Public Function addValues(key As String, value As String) As Integer 
       If Not firstValue Then 
           payload += "," 
       End If 
       payload += "{\x22key\x22: \x22" + key + "\x22, \x22value\x22:\x22" + value.ToString() + "\x22}" 
       firstValue = False 
       Return 1 
   End Function 
   Public Function publish() As Integer 
       Dim pay As ListOfByte = New ListOfByte 
       pay.Add("{\x22values\x22:[") 
       pay.Add(payload) 
       pay.Add("]}") 
       'mcThings modification 
       Dim paystring As String = pay.ToString() 
       Lplan.Publish("v2/things/" + topic, pay) 
       pay.Clear() 
       payload = "" 
       Thread.Sleep(10000) 
       Thread.ClearHardwareEvent() 
       firstValue = True 
       Return 1 
   End Function 
   Public Function setTopic(top As String) As Integer 
       topic = top  
       Return 1 
   End Function 
   Public Function getTopic() As String 
       Return topic 
   End Function 
End Class 

NTC Thermistor library

 Class NTCTermistor 
   Private beta As Integer 
   Private R25 As Integer 
   Public Sub New(betaIn As Integer, R25In As Integer) 
       'set Beta value 
       beta = betaIn 
       'Set R25 resistance value 
       R25 = R25In 
   End Sub 
   Public Function TemperatureFromResistance(resistance As Float) As Float 
       'returns temperature in Kelvin from resistance of thermistor using Beta parameter equation 
       Dim temp1 As Float = -1 * beta.ToFloat() / 298.15 
       Dim temp2 As Float = resistance / (R25.ToFloat() * temp1.Exp()) 
       Return (beta / temp2.Log()) 
   End Function 
   Public Function TemperatureFFromResistance(resistance As Float) As Float 
       'returns temperature in Fahrenheit from resistance of thermistor 
       Return (TemperatureFromResistance(resistance) * (9 / 5)) - 459.67 
   End Function 
   Public Function TemperatureCFromResistance(resistance As Float) As Float 
       'returns temperature in Celcuis from resistance of thermistor 
       Return TemperatureFromResistance(resistance) - 273.15 
   End Function 
End Class 

TMP102 library (built-in library, available within the IDE)

' 
' See the datasheet at http://www.ti.com/lit/ds/symlink/tmp102.pdf 
' 
Class Temperature 
   // Function returns the temperature in degree celcius or  
   // Float.NaN if something is wrong 
   Shared Function GetTemp() As Float 
       // Define the properties of the I2C peripheral and device address 
       Dim sensor As I2c 
       sensor = I2c.Create(250000, Pin.SCL, Pin.SDA, 0x48) 
       // Power up the sensor and give it some time to settle 
       Device.EnableTempSensor() 
       Thread.Sleep(40000) // See page 13 of the datasheet 
       // Read the sensor (only 2 bytes to read 
       Dim res As ListOfByte = sensor.Read(2) 
       // See Tmp102 documentation how to interpret the data (page 8) 
       Dim temp As Float = Float.NaN  
       If res <> Nothing Then 
           // Shift the partial part to the right nibble 
           Dim part As Float = res(1) >> 4 
           // Temperature partial is 1/16*n where n is between 0 and 15             
           part = part / 16 
           // Sign extend the byte to an integer 
           temp = res(0).SignExtend() + part 
       End If 
       // power off 
       Device.DisableTempSensor() 
       Return temp 
   End Function 
   Shared Function GetDieTemp() As Float 
       // Just get the temperature and return 
       Return Device.TempDie  
   End Function 
   Shared Function ToFarenheit(celcius As Float) As Float 
       Return (celcius * 9) / 5 + 32 
   End Function 
   Shared Function ToCelcius(farenheit As Float) As Float 
       Return (farenheit - 32) * 5 / 9 
   End Function 
End Class 

Viewing the information on thethings.iO!

Check out the recently posted walk-through by Carles Garriga on connecting to thethings.io dashboard! There is also a YouTube video (posted at the end of this project) for a visual walk-through!

thethings.io provides an easy to use and clean dashboard to easily visualize your data, set alerts and much more

Measuring boiling water

As seen in the cover picture of this project, we used one of the thermistors to measure the rise in temperature when we used our electric water boiler. The below is the graph (time lapse gif) from the real-time data going into the dashboard!

YouTube visual walk-through

Join our hub!

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Thanks for reading!