Getting Started with MicroPython and the SparkFun Inventor's Kit for micro:bit

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Contributors: LightningHawk
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Experiment 5: Reading an SPDT Switch

Introduction

In this experiment you will use your first digital input: a switch. The SPDT (Single-Pole, Double-Throw) switch is a simple way to select between two options, especially when paired with an “if” state. You will use that switch to select which of the two LEDs will blink.

Parts Needed

You will need the following parts:

  • 1x Breadboard
  • 1x micro:bit
  • 1x micro:bit Breakout with Headers
  • 2x LEDs (1 Red, 1 Yellow)
  • 2x 100Ω Resistors
  • 8x Jumper Wires
  • 1x SPDT Switch

Didn’t Get the SIK for micro:bit?

If you are conducting this experiment and didn’t get the Inventor’s Kit, we suggest using these parts:

Breadboard - Self-Adhesive (White)

PRT-12002
$4.95
36
micro:bit Board

DEV-14208
$14.95
5
SparkFun micro:bit Breakout (with Headers)

BOB-13989
$5.49
1
Jumper Wires - Connected 6" (M/M, 20 pack)

PRT-12795
$1.95
2
Mini Power Switch - SPDT

COM-00102
$1.50

COM-13761
Retired
LED - Basic Red 5mm

COM-09590
$0.35

Suggested Reading

Before continuing with this tutorial, we recommend you be somewhat familiar with the concepts in these tutorials:

Introducing the Single-Pole, Double-Throw (SPDT) Switch

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The Single-Pole, Double-Throw (SPDT) switch has a common pin in the middle and then two other pins that, depending on the location of the switch, are either connected to the common (center) pin or not. To read the switch in a similar way to a button, you connected the common pin to a digital General Purpose Input/Output (GPIO) pin on your micro:bit and the other pins to 3.3V and ground. It doesn’t matter which pin is which. When you move the switch, the common pin will either be HIGH (connected to 3.3V) or LOW (connected to ground).

Hardware Hookup

Ready to start hooking everything up? Check out the wiring diagram and hookup table below to see how everything is connected.

Pay special attention to the component’s markings indicating how to place it on the breadboard. Polarized components can only be connected to a circuit in one direction.

Wiring Diagram for the Experiment

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Having a hard time seeing the circuit? Click on the wiring diagram for a closer look.

Note: The full-sized breadboard power rails have a break down the middle. If you end up using the lower half of the power rail you will need to jump between the upper end and lower end.

Run Your Script

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Code to Note

pin0.read_digital()

Just as the write_digital() statement turns a pin on (1) or off (0), the read_digital() statement determines the state of a pin, which is either HIGH (1) or LOW (0). By building a circuit that connects 3.3V or ground to a pin, we can detect if a switch is thrown or a button is pressed.

What You Should See

Depending on the state of the switch, a different LED will blink. If you move the switch to connect the signal pin to 3.3V (HIGH) then the LED connected to pin P15 will blink. If you flip the switch and ground the signal pin, then the LED on pin P16 will start blinking, and LED 1 will turn off.

Troubleshooting

Light Not Turning On

The wires for the switch are right next to each other. Make sure that signal is in the center with voltage and ground on the outside pins. If you connect ground and voltage, your board will short out and shut down.

Make sure your power LED is on. If it is off, pull the signal wire and see if that changes anything. If you short circuit your micro:bit board, it will turn itself off to protect the circuitry.

Underwhelmed

No worries; these circuits are all super stripped-down to make playing with the components easy, but once you throw them together, the sky is the limit.