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#Post#: 2182--------------------------------------------------
NTC Thermistor Demo
By: AndrewPratt Date: December 11, 2017, 1:32 pm
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I am having a problem trying to get the Hackster thermistor demo
working that is outlined here
(
(HTM) https://www.hackster.io/mc-Things/iot-ntc-thermistor-temps-using-thethings-io-7f6934)
I ordered the same USP10972 thermistor and believe i have the
wiring correct but the values I'm getting out fluctuate a lot
and are never anywhere near valid. I also get a lot of not a
number errors so there's obviously something wrong! The hackster
description calls for a 100 ohm resistor but the one used in the
image is a 10k...I've tried both but neither solves the issue.
Ultimately I want to get it working on the 120 and then port it
to the 205 so that I can read water temp's outside under the
ice.
Here's the code I'm using to push the data to Losant. I also
have the onboard temp and battery being pushed as well but I've
remove that from the code below to keep it on topic.
Class Thermistor
Const USP10972_BETA As Integer = 3892
Const USP10972_R25 As Integer = 10000 '10kOhm
Const USP10972_DIVIDER_R1 As Integer = 10000 '10kOhm
Shared USP10972 As NTCTermistor
Shared Event Boot()
USP10972_DIVIDER_ENABLE = False
USP10972 = New NTCTermistor(USP10972_BETA, USP10972_R25)
End Event
Shared Event measureTemperature() RaiseEvent Every 10
Seconds
Dim LosantTopic As String = "losant/deviceID/state"
Dim losantPayload As Json = New Json
USP10972_DIVIDER_ENABLE = True
Device.EnableOpamp()
Thread.Sleep(10000)
Dim thermistorResistance As Float = USP10972_DIVIDER_R1
* (1 / ((Device.BatteryVoltage().ToFloat/
USP10972_VOLTAGE.ToFloat) - 1))
USP10972_DIVIDER_ENABLE = False
Device.DisableOpamp()
Dim tempPstring As String =
USP10972.TemperatureCFromResistance(thermistorResistance).ToStri
ng
Dim tempPJson As Json = New Json
tempPJson.Add("probeTemp", tempPstring)
losantPayload.Add("data", tempPJson)
Lplan.Publish(LosantTopic, losantPayload.ToListOfByte)
End Event
End Class
#Post#: 2183--------------------------------------------------
Re: NTC Thermistor Demo
By: mc-Josh Date: December 11, 2017, 2:50 pm
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Andrew,
What are USP10972_VOLTAGE and USP10972_DIVIDER_ENABLE defined
as? USP10972_DIVIDER_ENABLE is the pin that turns on the
voltage to the voltage divider and USP10972_VOLTAGE is the
voltage read from the divider. This voltage is then used to
calculate the resistance of the thermistor which corresponds to
a temperature. Can you show us how you have connected the 10k
resistor and thermistor to the mod120?
Thanks,
Josh
#Post#: 2184--------------------------------------------------
Re: NTC Thermistor Demo
By: AndrewPratt Date: December 11, 2017, 3:54 pm
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sorry I thought I'd included those. The wiring is the same as
the demo only I had wire leads added to the mc120 so that we
could prototype other things more easily.
Define PinMode Pin0 As AnalogInput Alias USP10972_VOLTAGE
Define PinMode Pin6 As DigitalOutput Alias
USP10972_DIVIDER_ENABLE
#Post#: 2185--------------------------------------------------
Re: NTC Thermistor Demo
By: mc-Josh Date: December 11, 2017, 4:14 pm
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Andrew,
It looks like you have the correct connections but that they may
be intermittent since they are not soldered. Can you solder the
connections to the thermistor and the resistor? Also, can you
measure the voltage being provided to the resistor divider and
the voltage at the sensor and ensure that the corresponding
voltage is correct for the temperature? We have made quite a few
of these and haven't had any issues.
Thanks,
Josh
#Post#: 2186--------------------------------------------------
Re: NTC Thermistor Demo
By: AndrewPratt Date: December 11, 2017, 4:23 pm
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So when I measure the 0 and 6 pin's and measure the voltage as I
dip the probe in hot and cold water it does change as you'd
expect it would.
This is the tempprobe code that I added to the project...
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
#Post#: 2187--------------------------------------------------
Re: NTC Thermistor Demo
By: AndrewPratt Date: December 12, 2017, 11:09 am
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Update. I decided that since I only had 1 temp probe attached to
the 120 I didn't need to use the resistor and pin's 0 & 6 so I
swapped it over to the ground and pin7 approach with the
internal pullup and it now works perfectly. This is the new
code.
Define PinMode Pin7 As AnalogInputPullUp Alias USP10972_VOLTAGE
Class ThermistorTheThings
Const USP10972_BETA As Integer = 3892
Const USP10972_R25 As Integer = 10000 '10kOhm
Const USP10972_DIVIDER_R1 As Integer = 100000 '100kOhm
Shared USP10972 As NTCTermistor
Shared Event Boot()
USP10972 = New NTCTermistor(USP10972_BETA, USP10972_R25)
End Event
Shared Event measureTemperature() RaiseEvent Every 10
Seconds
Device.EnableOpamp()
Thread.Sleep(10000)
Dim thermistorResistance As Float = USP10972_DIVIDER_R1
* (1 / ((Device.BatteryVoltage().ToFloat/
USP10972_VOLTAGE.ToFloat) - 1))
Device.DisableOpamp()
Dim battShort As Short = Device.BatteryVoltage()
Dim battFloat As Float = battShort / 1000
Dim battString As String = battFloat.ToString()
Dim tempTMP102string As String =
Temperature.GetTemp().ToString
Dim tempPstring As String =
USP10972.TemperatureCFromResistance(thermistorResistance).ToStri
ng
Dim LosantTopic As String = "losant/myDeviceID/state"
Dim losantPayload As Json = New Json
Dim mcJson As Json = New Json
mcJson.Add("probeTemp", tempPstring)
mcJson.Add("temperature", tempTMP102string)
mcJson.Add("batteryVoltage", battString)
losantPayload.Add("data", mcJson)
Lplan.Publish(LosantTopic, losantPayload.ToListOfByte)
End Event
End Class
#Post#: 2188--------------------------------------------------
Re: NTC Thermistor Demo
By: AndrewPratt Date: December 12, 2017, 11:14 am
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Now that I have it working on the mc120 how do you suggest I
port it to the 205 given that the 205 doesn't seem to support
the AnalogInputPullUp?
#Post#: 2189--------------------------------------------------
Re: NTC Thermistor Demo
By: mc-Josh Date: December 12, 2017, 2:05 pm
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Andrew,
You don't need the AnalogInputPullUp if you are providing the
pullup yourself. The CWF1B104F3950 thermistor does not need an
external pullup since it uses the 100k pullup on the mod120. The
USP10972 uses the 10k pullup that you added to the circuit.
Josh
#Post#: 2190--------------------------------------------------
Re: NTC Thermistor Demo
By: AndrewPratt Date: December 12, 2017, 2:45 pm
---------------------------------------------------------
Thanks Josh I now have it working on the Demo 205 as well using
the following.
Define PinMode Pin0 As AnalogInput Alias USP10972_VOLTAGE
Define PinMode Pin6 As DigitalOutput Alias
USP10972_DIVIDER_ENABLE
Class ThermistorTheThings
Const USP10972_BETA As Integer = 3892
Const USP10972_R25 As Integer = 10000 '10kOhm
Const USP10972_DIVIDER_R1 As Integer = 10000 '10kOhm
Shared USP10972 As NTCTermistor
Shared Event Boot()
USP10972_DIVIDER_ENABLE = False
USP10972 = New NTCTermistor(USP10972_BETA, USP10972_R25)
End Event
Shared Event measureTemperature() RaiseEvent Every 1 Hours
USP10972_DIVIDER_ENABLE = True
Device.EnableOpamp()
Thread.Sleep(10000)
Dim thermistorResistance As Float = USP10972_DIVIDER_R1
* (1 / ((Device.BatteryVoltage().ToFloat/
USP10972_VOLTAGE.ToFloat) - 1))
USP10972_DIVIDER_ENABLE = False
Device.DisableOpamp()
Dim battShort As Short = Device.BatteryVoltage()
Dim battFloat As Float = battShort / 1000
Dim battString As String = battFloat.ToString()
Dim tempTMP102string As String =
Temperature.GetTemp().ToString
Dim tempPstring As String =
USP10972.TemperatureCFromResistance(thermistorResistance).ToStri
ng
Dim LosantTopic As String = "losant/myDeviceID/state"
Dim losantPayload As Json = New Json
Dim mcJson As Json = New Json
mcJson.Add("probeTemp", tempPstring)
mcJson.Add("temperature", tempTMP102string)
mcJson.Add("batteryVoltage", battString)
losantPayload.Add("data", mcJson)
Lplan.Publish(LosantTopic, losantPayload.ToListOfByte)
End Event
End Class
#Post#: 2192--------------------------------------------------
Re: NTC Thermistor Demo
By: mc-Josh Date: December 13, 2017, 9:51 am
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That is great, what was the root of the problem?
Thanks,
Josh
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