## Exercise: Voltage Divider

#### Objective

Measure voltages and compute current flow in a resistive voltage divider.

Many sensor circuits we use will be built around an arrangement of series
resistances called a *voltage divider*. This is a fundamental
construction will will appear again and again.

Two resistors in series form a single current pathway, so a voltage
applied across the pair will cause the same current to flow through each
of them. However, the voltage drop across each resistor resulting from
that current is proportional to the resistance (V = i *
R), so the voltage at the intermediate node depends on the relative
resistances. In the simplest case, if both resistances are the same, the
voltage in the middle will be the average of the voltage at each end.

We will use the voltage divider structure to allow a variable resistance
(e.g. sensor or switch) to control the voltage at the intermediate point.
This is useful for us because the analog-to-digital converter on the
Arduino senses applied voltage.

#### Steps and observations

- Measure the exact resistance of each resistor.
- Carefully measure the voltage Vin applied across the series pair of
resistors.
- Compute the expected voltage V1 across the grounded
resistor: V1 = Vin * (R1 / (R1+R2)), where R2
is the 'upper' resistor connected to the positive supply and R1 is the
'lower' resistor connected to ground.
- Vary the input voltage and repeat; you should be able to convince
yourself that the intermediate voltage scales proportionately.
- Open the circuit and measure the actual current through the divider.
Compare against the predicted value i = Vin / (R1+R2).

#### Comments

Also see Wikipedia.

#### Other Files

- voltage-divider.fzz