# An Electronics Overview

In order to properly connect sensors to the Arduino board, we'll need to know a bit about electronics.

• In our electrical circuits, we will need to consider variables of voltage (V) and current (I). It might be helpful to think of a water hose as an analogous system. Voltage is like water pressure and current is like the velocity of the water passing through the hose.

• The following Introduction to Electronics should be helpful for those without any background in electronics.

• All of our circuits will include one or more resistors, which in our water-hose analogy are like sponges inserted inside the hose to slow the water flow.

• Ohm's Law relates the voltage (V) across a resistor (R) and the current (I) flowing through it as V = I R.

• In general, our voltage source will be 5 Volts.

• We'll want to limit the current in our circuits to minimize power consumption. For example, in a typical switch circuit we'll add a 10 K ohm resistor so that the current when the switch is closed is I = V / R or 0.0005 amps (0.5 milliamps).

• For the circuit of Fig. 1, the voltage measured at the pin with the switch open is 0 because no connection is made to the +5V source. When the switch is closed, there is a direct connection and a binary input pin would register a high'' value.

• The circuit above can be easily modified to measure a variable resistance, as shown in Fig. 2. The resulting variable voltage would have to be measured with an analog input pin.

• We'll see that a large number of sensors can be connected using the configurations shown above.

• It is often helpful to have a multimeter and/or an oscilloscope available to evaluate electrical circuits.