We're accustomed to touch screens, which are a part of nearly all mobile devices. Touch screens have been in use for a long time. By the mid-1980s, they were fairly standard on digital control systems (DCS), such as those used for refineries and coal power-generating stations.

Small applications have few inputs to change, so the need for a touch screen and its added complications is much less. Thus, thumb switches are widely used because of their simplicity and ruggedness.

What if your thumb switch controls appear not to work? Fortunately, these are easy to troubleshoot.

The first step in this process is to identify whether you have an octal (base 8), binary coded decimal (also called BCD, and it’s base 10), or hexadecimal (base 16) system. If you have thumb switches and don't understand these numbering systems, you need to do a little homework.

Your next step is to determine the position of the switch contact for each switch (e.g., up is open). You don't need to test what every combination of switch positions will render, nor do you have enough time to do so. In our next issue, we'll look at how to efficiently test a thumbwheel unit.