Digital Input and Output using the GPIO pins

GPIO pin numbering

The pins on the Raspberry Pi are number according to Broadcom’s GPIO numbering:

Library

To access the gpio pins import the library gpio:

import gpio

Function Reference

Open

Open()
Open(chipname)

Open gpio access to the chip specified by the optional parameter chipname. If chipname is not provided, the standart gpiochip of the Raspberry Pi will be opened.

• chipname
  • String
  • GPIO chip name
  • Optional parameter. Default value is gpiochip0

SetInput

SetInput(PinNumber)

Sets GPIO pin PinNumber as an input. The internal pullup-resistor will be set automaticly. Before using a GPIO pin, you should use either SetInput or SetOutput.

• PinNumber
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering

SetOutput

SetOutput(PinNumber)

Sets GPIO pin PinNumber as an output. Before using a GPIO pin, you should use either SetInput or SetOutput.

• PinNumber
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering

Write

Write(Pin, Level)

If Pin is configured as output, the voltage level level can be set to ground (low) or +3.3V (high).

• Pin
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering
• Level
  • Integer: 0 or 1

Example:

Write(4, 0)   ' Sets pin 4 to low (ground)
Write(4, 1)   ' Sets pin 4 to high (+3.3V)

Read

Status = Read(Pin)

If Pin is configured as input, the voltage level can be read. If the specified pin is at ground (low), Status will be 1. If the pin is at +3.3V (high) Status will be 0.

• Pin
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering
• Status
  • Integer: 0 or 1
  • 0 -> 3.3V
  • 1 -> Ground

Example:

Status = Read(4)   ' Reads the voltage level of pin 4

Trigger

Trigger(Pin)
Trigger(Pin, Duration)
Trigger(Pin, Duration, Level)

If pin Pin is configured as output, a trigger pulse at this pin will be emitted with a Duration in microseconds and a voltage level Level of low or high.

• Pin
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering
• Duration
  • Integer: 1 … 100
  • Duration in microseconds
• Level
  • Integer: 0 or 1
  • Voltage level of trigger

Example:

Trigger(4, 50, 1)  ' A 50 µs Trigger pulse at pin 4 with +3.3V (high)

Wait for Trigger

Status = WaitForTrigger(Pin)
Status = WaitForTrigger(Pin, Timeout)

Wait for a raising edge event at the specified pin Pin. Timeout is in seconds. Maximum timeout is 255s. Timeout an optional parameter.

• Pin
  • Integer: 0 … 53
  • Pin number according to Broadcom GPIO numbering
• Timeout
  • Integer: 1 … 255
  • Timout in seconds
  • Optional parameter: Default value is 1.
• Status

  • Integer: -1, 0, 1

    Value	Status
    -1	error
    0	time out
    1	rising edge detected

Example:

Status = WaitForTrigger(4, 1)  ' Pin 4; timeout 1s

Close

Close()

When closing a SmallBASIC program, gpio access will be automatically closed. If you want to manually close gpio access, use this function.

Example Code

1. LED

In the following image you can see how to wire a LED.

Depending on the type of LED you need a certain resistor. When using the LED without a resistor, you will destroy the LED and maybe even parts of your Raspberry Pi.

When you buy a LED, look for two important values in the specification: Forward Voltage and Forward Current. The third important value is the Supply Voltage. In case of a Raspberry Pi it is 3.3V. Online you can find many LED resistor calculators. But if you want to see your LED blinking without studying to much and you don’t expect maximum brightness, then go for 220 Ohms or even 1000 Ohms.

Connect the resistor to pin 4 and the LED to ground.

import gpio

gpio.Open()
gpio.SetOutput(4)

for ii = 1 to 10
  v = !v
  gpio.Write(4, v)
  delay(100)
next

2. Button

In the following image you see the wiring of a push button. When you press the button, the circuit will be closed, otherwise the circuit is open. The button is connected to pin 4 and ground. An internal pullup resistor will be enabled automatically.

import gpio

v = 0

gpio.Open()
gpio.SetInput(4)

while(1)
  print gpio.Read(4)
  delay(500)
wend

3. Trigger

import gpio

v = 0

gpio.Open()
gpio.SetOutput(4)

for ii = 1 to 10
  gpio.Trigger(4)
  delay(200)
next

4. Wait for Trigger

import gpio

v = 0

gpio.Open()
gpio.SetInput(4)

result = gpio.WaitTrigger(4, 5)

select case result
  case  0: print "Time out"
  case  1: print "Rising edge detected"
  case -1: print "Error"
end select