Nuts and Volts - April 2014

connection, so the circuit is broken and the LED does not light up. When you press the button, the LED will light up.

; Is the LED on or off?

; Press the button and see if the LED comes on and stays on while the button is pressed.

Take a moment to think about how the pins on the breadboard are connected by the pushbutton when it is open (unpressed) and closed (pressed). Figures 8 and 9 show these two states

Turn the LED off with a pushbutton – analog.

Let’s rebuild the circuit so that the LED is normally on, and goes off only if the button is pushed. Note from the schematic in Figure 10 that the current will flow from 5V through the resistor and the LED to ground, but in Figure 11 the current will flow from 5V through the switch to ground. The reason it flows through the switch and not the LED is that the switch has near zero resistance, while the LED has a relatively higher resistance. Current (like water) flows down the path of least resistance.

Check off when complete:

; Make sure the power is off before building the circuit.

; Build the circuit as shown in Figure 10.

; Apply power to the circuit.

; Is the LED on or off when the button is not pushed?

; Push the button to verify that the LED turns off while the button remains pushed as shown in Figure 11.

; Briefly explain why the LED is on when the button is not pressed, and why it turns off when the button is pressed.

Lab 2: Reading a Pushbutton — Digital.

When an Arduino pin is set to the input mode, it may be used to determine if the pin is exposed to a higher or lower voltage. In the design shown in Figure 12, pin 12 is connected to a 10 KW resistor that is connected to ground. The pin is also connected to a pushbutton that is connected to five volts.

When the button is not pushed, the pin is exposed to zero volts and the Arduino software will read this as a LOW. If the button is pushed, then the pin is connected to both the 10 KW resistor to ground and to the five volt supply.