7) potentiometer and preset

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Mand Labs presents

Potentiometer

• Variable Resistor with 3 terminals

• Side Terminals: 1 and 3

• Middle Terminal: 2

• Rotate the knob and resistance changes

• Smaller version of Rheostat

Potentiometer

Variable & Fixed Resistance• A resistor has only two ends

• Variable Resistance: Use terminal 2 and any side terminal (1 or 3)

• Fixed Resistance: Use side terminals (1 and 3)

• Rotate the knob and resistance changes

• Examples: Fan Regulator, Volume Control

Schematic Symbol

Inside Potentiometer

Inside Potentiometer

• Resistance between 1 and 3 = Resistance between 1 and 2 + Resistance between 2 and 3

• R13 = R12 + R23

• R13 = Fixed Value = Imprinted on the component

• Rotate towards terminal 1: R12 decreases and R23 increases; total sum of R12 and R23 remains constant

• Rotate towards terminal 3: R12 increases and R23 decreases; total sum of R12 and R23 remains constant

Preset• Same as potentiometer

• More Portable

• Slot on the preset

• Insert screw driver inside slot to change resistance

• Variable Resistance: (1,2) or (2,3)

• Fixed Resistance: (1,3)

Schematic Symbol

Recommendation: In booklet, we have used symbol of a potentiometer to denote a preset. You can safely use a preset in place of potentiometer.

Preset as Voltage Divider

• Provide Vcc to terminal 1

• Provide ground to terminal 3

• Take output from terminal 2

• Output at terminal 2: Variable Voltage

• Rotate preset and measure voltage at pin 2

Preset as Voltage Divider

Preset as Voltage Divider

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