Push Buttons

Push Buttons

Push Buttons

• Momentary switches that make (or break) electrical contact when pressed
• “Normally open” buttons complete a circuit when pressed (this is what is in the kit)
• “Normally closed” buttons break a circuit when pressed (we won’t use these in class)

Push Button Orientation

• Buttons have four pins and are designed to go across the center of the breadboard

Push Button Connections (Normally Open)

• In the picture, each set of pins “vertically across” from each other are always connected (purple and blue)
• Each set of pins “horizontally next to” each other are not connected until the button is presed

Push Button Connections (Normally Open)

• When button is pressed, all four pins are connected (yellow pins)

Goal

• We want to use the button to send a binary (on/off) signal
• Since this is a digital input, we can use HIGH (3.3v) and LOW (gnd)

First Version

First Version - Problem

• When button is pressed, input pin is connected to gnd (LOW)
• When button is open, is it LOW or HIGH?

Floating Input

• When an digital input is neither exactly LOW (0v) or HIGH (3.3v), we say it is floating
• This means it is somewhere between 0-3.3v
• Should 2.4v be LOW or HIGH?
• Let’s fix this

Second Version

Second Version Problem

• When button is open, we have HIGH (fixed)
• When button is pressed, we connect power (3.3v) to gnd (BAD!)

Final Version

Final Version - With Pull-Up Resistor

• We use a large resistor (10k) to “pull-up” the input to 3.3v when the button is open (HIGH)
• When the button is pressed, the input goes to gnd (LOW), and we no longer have short-circuit from power to ground

IMPORTANT

• ALWAYS USE A PULL-UP RESISTOR WITH BUTTONS
• Otherwise you can damage the Photon 2 permanently

Exercise 1

1. Turn LED on only while button pressed
2. Toggle LED on and off after each time button is pressed
3. Connect 3 LEDs (D3, D4, D5) and turn all on and off at once
4. Then turn lights on and off in a sequence (e.g. (3 states)

Exercise 2

1. Turn on red LED on only while button pressed
2. Toggle red LED on and off after each time button is pressed
3. Generate 1 new random color each time button is pressed
4. Make each button press move LED through a sequence of colors

Credit

• Sparkfun
• SVG
• Images created with Fritzing