Trimpot

 
Trimpot

What is a trimpot? A trimpot or trimmer potentiometer is a small potentiometer which is used for adjustment, tuning and calibration in circuits. When they are used as a variable resistance (wired as a rheostat) they are called preset resistors. Trimpots or presets are normally mounted on printed circuit boards and adjusted by using a screwdriver. The material they use as a resistive track is varying, but the most common is either carbon composition or cermet. Trimpots are designed for occasional adjustment and can often achieve a high resolution when using multi-turn setting screws. When trimmer potentiometers are used as a replacement for normal potentiometers, care should be taken as their designed lifespan is often only 200 cycles. Trimpot definition Trimmer potentiometers and preset resistors are small variable resistors which are used in circuits for tuning and (re)calibration. Types of trimpots Several different versions of trimpots are available, using different mounting methods (through hole, smd) and adjusting orientations (top, side) as well as single and multi-turn variations. Single turn Single turn trimmers/presets are very common and used where a resolution of one turn is sufficient. They are the most cost effective variable resistors available. Multi turn For higher adjustment resolutions, multi-turn trimpots are used. The amount of turns varies between roughly 5-25, but 5, 12 or 25 turns are quite common. They are often constructed using a worm-gear (rotary track) or leadscrew (linear track) mechanism to achieve the high resolution. Because of their more complex construction and manufacturing, they are more costly than single turn preset resistors. The lead screw packages can have a higher power rating because of their increased surface area. Trimpot symbols The following IEC symbols are used for trimpots and preset resistors. Although this are the official symbols for occasionally adjusted resistors, the standard symbols for [… read more]

Variable resistor

 
Variable resistor

What is a variable resistor? A variable resistor is a resistor of which the electric resistance value can be adjusted. A variable resistor is in essence an electro-mechanical transducer and normally works by sliding a contact (wiper) over a resistive element. When a variable resistor is used as a potential divider by using 3 terminals it is called a potentiometer. When only two terminals are used, it functions as a variable resistance and is called a rheostat. Electronically controlled variable resistors exist, which can be controlled electronically instead of by mechanical action. These resistors are called digital potentiometers. Variable resistor definition A resistor of which the ohmic resistance value can be adjusted. Either mechanically (potentiometer, rheostat) or electronically (digital potentiometer). Types of variable resistors Potentiometer The potentiometer is the most common variable resistor. It functions as a potential divider and is used to generate a voltage signal depending on the position of the potentiometer. This signal can be used for a very wide variety of applications including: Amplifier gain control(audio volume), measurement of distance or angles, tuning of circuits and much more. When variable resistors are used to tune or calibrate a circuit or application, trimmer potentiometers or trimpots are used, this are mostly small potentiometers mounted on the circuit board, which can be adjusted using a screwdriver. Rheostat Rheostats are very similar in construction to potentiometers, but are not used as a potential divider, but as a variable resistance. They use only 2 terminals instead of the 3 terminals potentiometers use. One connection is made at one end of the resistive element, the other at the wiper of the variable resistor. In the past rheostats were  used as power control devices in series with the load, such as a light bulb. Nowadays rheostats are not used as power control anymore [… read more]