In January 2012 we introduced the Thermistor hash command, which makes the use of spreadsheets largely unnecessary. SPLat/PC can now do all the hard work for you.

This section will introduce you to the various parts of the spreadsheet, in a brief overview.

When you first look at the thrmstr8.xls spreadsheet it may appear rather cluttered and a bit daunting. Don’t worry. If you have little of no experience with spreadsheets think of it a a form where you fill in a few squares and a whole heap of calculations are done automatically for you. To change the number in a square (cell) simple click on it and type. Do not change cells you are not specifically told to change.

You will see a number of coloured panels, some buttons, some graphs and a lot of numbers. Here are some of the main parts of the spreadsheet:

System Parameters.

These are, in the main, the numbers you need to supply. They are arranged into 4 sub-groups, which are:

• The temperature range you need to cover
• The specification of the thermistor you are using
• The parameters of the SPLat board you are using
• Two values, a voltage Vfeed and a resistance Rfeed, that need to be optimized.

All of the above are to some degree under your control.

Polynomial coefficients

These numbers are the ultimate outcome of the process. They will get coded into your SPLat program to perform the conversion from raw readings to degrees Celsius. Don’t worry about the underlying math … just have faith.

Graphs

The two graphs show the performance of the measurement system. One is the curve of raw analog input counts versus temperature. This graph is used to make Excel calculate the all-important polynomial coefficients for us. The other graph shows the resulting measurement resolution versus temperature.

Buttons

There are two buttons, [FindBestVfeed] and [FindBestRFeed]. These trigger some ‘under the hood’ macro code that helps you find optimum settings. The [Q] button will be introduced later.

Calculated data columns

There a quite a number of columns of calculated data. You may inspect these but you must never type into them.

The remaining bits will be explained when required.

The next sections go through the step by step procedure required to design and program a temperature measurement using thermistors and a SPLat.