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Variable Resistors: Identifying Potentiometers

written by: Terry Ligard • edited by: Lamar Stonecypher • updated: 1/5/2010

Potentiometers allow one to change their resistance and are invaluable when it comes to building circuit boards. Although there are many types of potentiometers, the one often used in robotics is the trimpot because it can fit into a breadboard.

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    For those beginning to learn about robotics, particularly in the area of building circuits, you may have come across the question of how to change the brightness of a LED, without having to keep switching parts. This is the concept I will be discussing. Quite simply, the solution to this issue is a potentiometer.

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    Potentiometers   Although you may not have heard of the word potentiometer, you may have heard of variable resistors. In fact, potentiometers are variable resistors. Specifically, they function to alter their resistance via a knob or dial. You have probably used one before by adjusting the volume on your stereo or using a light dimmer.

    Potentiometers have a range of resistance, that is, they can be attuned from zero ohms to whatever maximum resistance that is specific to it. For example, a potentiometer of 300 Ω can be adjusted from 0 Ω to its maximum of 300 Ω.

    When it comes to installing a potentiometer onto a solderless breadboard, however, only a specific type of potentiometer can fit. (Many are shaped in a way that they can not fit into the breadboard.)

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    Trimpot   Trimpot is another term for trimmer potentiometer. They are useful in that they are lightweight, small, and usually fit into solderless breadboards.

    On the other hand, it is tedious to change their control dial. Instead of knobs that can be changed with your own fingers, trimpots require a screwdriver, or some similar tool with a flat end. Moreover, trimpots are more fragile than larger potentiometers. They can damage after their dial has been adjusted about 100 times compared to larger potentiometers that can be adjusted thousands of times without damage.

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    Turning the Dial

    Multiturn trimpot   Most potentiometers require only a single turn of their dial to adjust between their minimum and maximum value, or from 0 Ω to whatever maximum ohm. This allows for a simple assessment of whether the dial is at the minimum, half way, or at its maximum.

    There also exists potentiometers that require multiple turns. For instance, a multi-turn potentiometer may require up to 30 turns to cover the entire range in ohms. The advantage of this potentiometer is that it allows for small incremental changes. Also, if vibration to the dial causes a partial turn, the effect may even go unnoticed, as opposed to a single-turn dial.

    A multi-turn trimpot is identified by a metal screw located to the side of the trimpot. A single-turn trimpot usually has a plastic dial. Due to their greater level of sophistication, multi-turn trimpots are more expensive.

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    At one point or another in your robotics career, you will have the need to conveniently change between resistors, such as different LEDs, and the way to do this is to use a potentiometer. There are many kinds of potentiometers, but ones that are often used in solderless breadboards are trimpots. All potentiometers have a mechanism by which their resistance value is changed, whether it is a finger knob or a dial requiring a screwdriver. Moreover, the knob or dial can be adjusted across its range in ohms by a single turn or multiple turns, and this poses several advantages and disadvantages.

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    About the Author

    Terry Ligard is a fourth year mechanical engineering student at the University of Alberta. Terry has several months of experience building electromechanical transporters.