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====== Temperature Sensor ======

There are many uses for devices that sense temperature. Refrigerators,
heaters, air conditioners, automobiles, etc.. all make use of devices that
sense temperature.

There are several different kinds of temperatures sensors. There are
PT100, NTC, and PTC thermistors, and other chip-type sensors such as the
DS1620.

We will take a look at the NTC thermistor and interface it with the Cubloc.
The NTC thermistor is a temperature-sensitive resistor. Depending on the
temperature, the value of resistance will change. By reading the value of
this resistance, we can determine the temperature.

A common NTC thermistor resembles a diode. With this thermistor, we can
sense temperatures between -30 and 250 degrees Celsius.

{{ :cubloc:temperature_sensor:ntcsensor.png?nolink |}}

You can acquire an R-T (Resistance – Temperature) conversion table from
the maker of the thermistor. The following is a diode-type 10Kohm NTC
thermistor R-T conversion chart and table.

{{ :cubloc:temperature_sensor:temptable.png?nolink |}}

For connecting the sensor to the Cubloc, please refer to the following circuit
diagram. To protect against voltage surges, a zener diode is recommended,
especially if the thermistor is attached to a long probe wire.

{{ :cubloc:temperature_sensor:ntcsch.png?nolink |}}

As you can see in the circuit diagram, we will be using an ADC (Analog-toDigital)
converter to read the voltage across the sensor. The A/D converter
will convert the voltage into a value between 0 and 1024.

The most important part of this application note is the following table which
converts the temperature and voltage to an A/D value between 0 and 1024.
(Only some of the temperatures are shown.)

{{ :cubloc:temperature_sensor:temptable2.png?nolink |}}

<code xbasic>
'
' NTC THERMISTOR READ TABLE
' 10K DIODE TYPE
'
Const Device = cb280

Const Integer TH_TABLE = (992,990,989,987,985,983,981,979,977,975,
973,970,968,965,963,960,957,954,951,948,
945,942,938,935,931,927,923,919,915,911,
907,902,898,893,888,883,878,873,868,862,
857,851,845,839,833,827,821,815,808,802,
795,788,781,774,767,760,753,746,738,731,
723,716,708,700,692,684,677,669,661,652,
644,636,628,620,612,604,596,587,579,571,
563,555,547,538,530,522,514,506,498,491,
483,475,467,460,452,445,437,430,422,415)
Dim a As Integer,b As Integer

Do
    b = Tadin(0)
    If b > 990 Or b < 400 Then
        Debug "Out of Range" 'Check short or open th.
    End If
    
    For a=0 To 100
        If b > TH_TABLE(a) Then Exit For
    Next
    
    Debug Dec a,cr
    
    Delay 500
Loop
</code>


By using the TADIn command for AD conversion, the Cubloc will
automatically calculate the average of 10 A/D conversion reads for more
precise results. The sample program shown here will be able to sense
between 0 and 100 degrees. A minor modification to the code would allow
a larger temperature range.

The formula for acquiring the A/D conversion value from the R-T table is as
follows:

{{ :cubloc:temperature_sensor:tempfomula.png?nolink |}}

THR is the resistance value. 1000 is for a 1K Ohm resistor and 5 is for 5
volts. The 10 bit A/D converter of the Cubloc will return a value between 0
and 1024. Therefore, to get the A/D value, you must multiply the result, V,
by 204.8. A chart can be made by plotting this formula in a spreadsheet.