Potentiometers (or ‘Pots’) can sometimes be a little confusing. People have asked me before what it is and how to wire one up, what do the numbers mean (1,2,3) and what do the letters mean (A,B)? So here we go, this is by no means comprehensive but should provide a very simple, very short introduction to potentiometers. There are many more in depth articles around the net but sometimes one can easily become confused amongst the jargon.
A potentiometer is a ‘variable resistor’ of sorts that allows you to control the amount of resistance. This is obviously ideal for things like gain or volume controls as otherwise you would have to have a switch that switched between many individual resistors, bringing them in and out of the circuit path, in order to achieve increase or decrease in volume (or whatever it is you are controlling). Either that or be satisfied with a fixed volume, but we want flexibility right?
Numbering
On schematics and layouts I see the numbers 1, 2 and 3. What do these denote?
It is actually pretty simple, the numbers are a way of navigating the lugs of the pot.
So here is a picture of what a pot is likely to look like if you are viewing a layout of some kind (PCB, Perf, Vero etc). Bare in mind that this is the backside of the pot with the shaft facing downwards. One of the things that always got me (and still does!) is remembering to read the numbers correctly depending on whether the pot is backside down or backside up.
Tapers (A, B)
So now that the numbering is down what about the letters that appear in the pot’s name? Something like A100k or B150k?
The A and B denote the ‘taper’ of the pot. The graph below explains it better than words can but basically A stands for Audio or Logarithmic taper and B stands for linear taper. A logarithmic taper is often preferred as a volume control because of how our brain interprets volume change. This is not always the case however. The best thing is to use the taper that the schematic requests, but there is no harm in experimenting.
You’ll have to excuse the crudeness of the graph, but it illustrates the text well.
That’s really all there is to know at a basic level. Hopefully now you can recognise how to wire up a potentiometer quite simply.
If you are interested in further reading then you should check out the rather more advanced, more electronics based ‘The Secret Life Of Pots’ by the great R.G. Keen. http://www.geofex.com/Article_Folders/potsecrets/potscret.htm