CHAPTER 14 ■ VARIABLE RESISTORS
You can adjust all potentiometers down to zero ohms (no resistance). The value printed on the
potentiometer indicates its maximum value. For example, you can adjust a 500 W potentiometer from
0 W up to 500 W. You can adjust a 10 kW potentiometer from 0 W to 10 kW.
There are a wide variety of potentiometer sizes and packages available. However, like switches, only a
small subset of potentiometers fit into a solderless breadboard. The other potentiometer sizes tend to have
oddly spaced or thick leads.
Trimpot
Trimpot is short for trimmer potentiometer. Sometimes they’re called trimmers. They’re lightweight, take up
very little space, and most fit into solderless breadboards (see Figure 14-2).
Figure 14-2. A breadboard-compatible single-turn trimpot
Unlike full-size potentiometers, trimpots don’t have finger-friendly control knobs. Instead, they’re
adjusted with a small screwdriver. This can be a pain when you want to make an adjustment; however, it
does reduce the likelihood of accidental changes. Trimpots are often used for values that won’t be adjusted
very often and are usually set by a service technician as opposed to a consumer.
Trimpot dials are more delicate than full-size potentiometers. Trimpots wear out after as little as a
hundred turns, as opposed to tens of thousands of turns for a full-size potentiometer. This shouldn’t be an
issue since trimpots are adjusted less often.
Recall Sandwich’s sensor balancing dial. The robot needs to be in place on a track to determine if the
left pair of sensors sees the same values as the right pair of sensors. However, the dial rarely needs tweaking
after the initial adjustment is made to compensate for manufacturing variations or soldering inconsistencies.
For those reasons, Sandwich has a tiny hole for a screwdriver to access a trimpot (see Figure 14-3) instead of
a full-size, externally mounted potentiometer.