I am designing a PCB for a VFD clock I want to build and I have come across something in a schematic for a voltage regulator that I have no idea what it means.


I have circled what I do not understand in red. I'm curious as to what this is supposed to denote. I do not want to fry any chips or blow up VFDs.

  • 4
    \$\begingroup\$ The arrow and the resistor it points to make up the symbol for a potentiometer, also called a variable resistor. \$\endgroup\$
    – bitsmack
    Commented Mar 14, 2017 at 15:57
  • \$\begingroup\$ Oh, ok. Now in regards to that, could I calculate the exact resistance needed and use a wirewound or metal film resistor? Or would you recommend following the schematic and using a potentiometer? \$\endgroup\$ Commented Mar 14, 2017 at 16:30
  • 1
    \$\begingroup\$ It depends on whether the "adjustability" is a required feature. If the tolerances on the rest of the circuit dictate that some adjustment is required you should leave it in, though replacing it with a high precision resistor during final test is certainly a procedure that some folks employ to lock down the values. If the circuitry needs adjusting or calibrating later in it's life, you should definitely leave it in. \$\endgroup\$
    – Trevor_G
    Commented Mar 14, 2017 at 17:06
  • \$\begingroup\$ If you plan on going the "lock-down-Value" way, I suggest you replace the pot in the schematic with a spot for a fixed resistor AND a 3 pin jumper where you can easily connect a "tool" to calibrate it. \$\endgroup\$
    – Trevor_G
    Commented Mar 14, 2017 at 17:09

1 Answer 1


That's called a potentiometer, or "pot" for short.

It is a fixed resistor between the two ends shown top and bottom in your schematic. The third terminal, shown with a arrow in a standard schematic symbol, is a wiper that contacts the resistive strip in a place that depends on how the pot is adjusted.

The net result is a fixed resistor end to end with a variable tap someplace within that resistance.

One use of these things is to make a variable voltage divider. Feed the fixed voltage into one end, ground to the other, and a variable voltage comes out the tap depending on how the pot is set.

This is also the basis for most old volume knobs. One wrinkle with adjusting volume is that humans perceive volume logarithmically. There are special pots called "log taper" where the resistance along the fixed resistor varies logarithmically, not linearly. If a pot isn't specified to have log taper, then you can assume it has linear taper. Log taper pots are harder to find now that volume controls are generally implemented digitially.

In your schematic, the pot is used as a rheostat. That's a 2-terminal variable resistor. That's what you get when you short the wiper to one of the ends, or leave one of the ends open.


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