RoboCon

# GPIO

The GPIO (General Purpose Input Output) allows you to turn on LEDs, react to button presses, or do just about anything.

Our BrainBox has 4 GPIO pins that you can control. Before you do anything with a pin, you must first set its mode.

There are 4 modes:

Mode Python Description
Digital Output robot.OUTPUT Allows you to write a high or low signal
Digital Input robot.INPUT Allows you to read a high or low signal
Analog Input robot.INPUT_ANALOG Allows you to read a voltage, like a voltmeter
Pullup Input robot.INPUT_PULLUP Like input, but uses a weak pullup resistor

TIP

The GPIO are numbered 0-3

# Python

To write a digital signal on pin 0:

R.gpio[0].mode = robot.OUTPUT
R.gpio[0].digital = True

To read a digital signal on pin 1:

R.gpio[1].mode = robot.INPUT
print(R.gpio[1].digital)

To read an analog signal on pin 2:

R.gpio[2].mode = robot.INPUT_ANALOG
print(R.gpio[2].analog)

To read a pullup signal on pin 3

R.gpio[3].mode = robot.INPUT_PULLUP
print(R.gpio[3].digital) # Note that this output will be inverted - True when the connnection is open, and False when closed.

TIP

All modes can be used on all pins. Note that you only need to set this mode once in your code, not every time you read an input or send an output.

Here's a more complete example:

import robot
import time

R = robot.Robot()

R.gpio[0].mode = robot.INPUT
R.gpio[1].mode = robot.INPUT_ANALOG
R.gpio[2].mode = robot.OUTPUT
R.gpio[3].mode = robot.INPUT_PULLUP

outputState = False

while True:
    # Read the values of 0 and 1
    print(R.gpio[0].digital)
    print(R.gpio[1].analog)

    # Switch output state and send it to 2
    outputState = !outputState
    R.gpio[2].digital = outputState

    # Read the value of 3
    print(R.gpio[3].digital)

    # Pause for 2 seconds
    time.sleep(2)

# Blockly

The GPIO blocks can be found in the GPIO section, and function similarly to the python.

# Pull-ups

The BrainBox possesses the ability to enable a built-in pull-up resistor on any input pin. This takes a small amount of explanation.

Normally, input pins are not connected to anything - known as “floating”. In this state, they might read high or low, or different values depending on their environment (due to anything from cosmic rays to the wiring in the building). This is obviously not good for consistent control.

Many pieces of off-the-shelf electronics that have some form of standard I/O output will connect this pin to 5V (high) and 0V (low) when required, so this is not a problem. However, for simple electronics, a microswitch for example, you would normally be required to connect a resistor between the input pin and 5V (a pull-up resistor), or between the input pin and 0V (a pull-down resistor) to keep the input in a known state until the switch overrides it by connecting directly to the opposite state.

However, the built-in pull-up resistor alleviates this need. It essentially wires in a resistor connected to 5V, meaning that when this option is enabled, an input pin will “default” to being high. This means you can simply connect a switch between the input pin and a ground pin without any need of resistors - when the switch is open, the pin will read high; when closed, it will read low.

An example weak pull up

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