[Guide] Analog to Digital converters explained


Staff member
Home automation systems that are a step beyond your basic "X-10" light control usually consist of a mechanism for controlling and monitoring digital input and output modules. These systems may include an Ocelot with SECU16(I) and/or RLY8-XA expansion units, Caddx Security Systems, Elk M1 Gold Systems, JDS Stargate and others. Their basic functionality of simple, digital inputs and outputs serves most automation and security purposes.

What happens when you want to expand your automation system to include custom measurements such as temperature, water softener salt level indicator, distance measurement, weight measurements, etc...? You could use a "canned" system to measure temperature for instance but what if you want something more versatile? Well one answer would be to have a monitoring system that incorporated a way to measure "analog" inputs via an analog to digital converter. This way you could now directly measure these items with your automation system.

This Guide will describe basic analog to digital converter principles. Its intent is to introduce this topic and also describe how one would go about the necessary calculations needed for general home automation purposes. I would like to thank Guy Lavoie for kindly reviewing this Guide as his efforts made this a greatly improved article.

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Just another comment on a method to determine the equation, given multiple pairs of 'x' and 'y' coordinates.  You can always use Excel to determine the equation, especially if the results are 'non-linear' (i.e. do not produce a near straight line when graphed).
To do this, click on the data series in the chart itself, then select 'Add Trendline' in the 'Chart' menu.  Select what type of fit you want to try (I suggest polynomial if non-linear) and the order (try two, then go up if the results do not fit well).
You will then see another chart line with the equation taken into consideration.  If this is a close enough match for you click on the data series line again, then select 'Format Trend Line' then the 'Options' tab.  Select 'Show Equation' which will then show you the resulting equation you want to use on the chart.
You can experiment with different type of trend fits as well as number of polynomial expansion numbers to get the best one that matches your data series.