# Potentiometers

Potentiometers are essentially potential dividers with one significant difference. You can variate the voltage that is being outputted. The resistance, and consequently the voltage, can be changed by adjusting the position of the knob. For reference, here’s the link to the post on potential dividers:  ‘https://thelectronicsblog.wordpress.com/2015/11/11/potential-dividers’

Above is a diagram of what a potentiometer physically looks like. Rotating the knob directly changes the position of the wiper. The position that the wiper is in dictates the voltage outputted from the wiper wire.

To explain this more easily, imagine that the two resistors from the potential divider diagram have been squished together, and the insulated coating has been removed.

Assume that R1 and R2 in the diagram on the left are each 5k. They have been squished together on the diagram on the right. This forms a 10k piece of resistive material . But because the position of the Vout wire is approximately half way down, it is the same as having a 5k resistors on each side.

Now assume that the Vout wire is instead now 3/4 of the way down the resistive material. This is equivalent to having a 7.5k resistor as R1, and a 2.5k resistor as R2.

Now that the premise behind potentiometers has been explained, here’s the original physical diagram shown side by side with what the internal wiring of a potentiometer would actually look like:

Hopefully you now understand how a potentiometer works. However, if you have any questions, please don’t hesitate to ask.

# Resistor colour codes

#### 4 Band resistor colour coding

On a resistor which has four bands of color, the first and second bands represent a two digit number. This can be found by looking at which number value the colours represent. In the Figure below, the first band is brown and the second is black. This gives use 10 as our two digit number. Next, you look at the third colour, which represents the multiplier. You take this value and multiply it by the two digit number. In this case, it would be 10 x 100Ω. This would give us a resistor value of 1kΩ.

# Resistors in series and parallel

Resistors in a series alignment

Calculating resistance in series is the easier of the two. You simply add them together to find the total resistance.

Resistors in a parallel alignment

When calculating resistance in parallel, it’s a little more complicated. But so long as you follow the formula, it should be okay. In addition to this, you can double check your results, because it should always be lower than the value smallest resistor.

# Potential dividers

A potential divider reduces the voltage in a circuit. If R1 and R2 are equal, the voltage at Vout will be half of that at Vin.

Here is a condensed equation to calculate the voltage at Vout:

This can also be calculated by finding the current that flows through the potential divider. To do this you find the total volt drop and divide it by the total resistance (because the voltage drops to 0, the total volt drop is equal to Vin).

After the current has been found, Vout can be calculated my multiplying R2 by the current(i) (you use R2, because this calculation finds the volt drop across the resistor, so Vin – volt drop across R1 = volt drop across R2 = Vout).