|Home | Site Map | Components | 555 | Symbols | Study | Books | Construct | Solder | Projects | FAQ | Links | Privacy|
Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a potentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require further adjustment.
Variable resistors are often called potentiometers. They are specified by their maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is 6mm.
The resistance and type of track are marked on the body:
Some variable resistors are designed to be mounted directly on the circuit board, but
most are for mounting through a hole drilled in the case containing the circuit with
stranded wire connecting their terminals to the circuit board.
Linear (LIN) and Logarithmic (LOG) tracks
Logarithmic (LOG) track means that the resistance changes slowly at one end of the track and
rapidly at the other end, so halfway along the track is not half the total resistance!
This arrangement is used for volume (loudness) controls because the human ear has a logarithmic
response to loudness so fine control (slow change) is required at low volumes and coarser
control (rapid change) at high volumes. It is important to connect the ends of the track the
correct way round, if you find that turning the spindle increases the volume rapidly followed
by little further change you should swap the connections to the ends of the track.
Rheostats are often used to vary current, for example to control the brightness of a lamp or the rate at which a capacitor charges.
If the rheostat is mounted on a printed circuit board you may find that all three
terminals are connected! However, one of them will be linked to the wiper terminal.
This improves the mechanical strength of the mounting but it serves no function
This arrangement is normally used to vary voltage, for example to set the switching
point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit.
If the terminals at the ends of the track are connected across the power supply then the
wiper terminal will provide a voltage which can be varied from zero up to the maximum of
Presets are much cheaper than standard variable resistors so they are sometimes used in projects where a standard variable resistor would normally be used.
Multiturn presets are used where very precise adjustments must be made. The screw
must be turned many times (10+) to move the slider from one end of the track to the other,
giving very fine control.
Rapid Electronics have kindly allowed me to use their images on this page. Rapid stock a wide range of components, tools and materials for electronics. I am happy to recommend them as a supplier for individuals and education. In my experience their standard delivery really is rapid!
© John Hewes 2014, electronicsclub.info (based in the UK)
No part of this website may be reproduced in any way commercially without my prior permission.
This website does not collect any personal information unless you contact me by email. If you send me an email your name, email address, and any other personal information you supply will be used only to respond to your message. Your personal information will never be given to any third party without your permission.
This website displays affiliate advertisements. If you click on these advertisements the advertiser will know you came from this site and I may be rewarded if you become their customer. No personal information is passed to advertisers.
This website uses StatCounter cookies to estimate the number of unique visitors. No personal information is stored in the cookies. If you would like further information or wish to refuse these cookies please visit the StatCounter website.
To learn how to delete and control cookies from your browser please visit AboutCookies.org.