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Digital outputs

Pigeon computers are equipped with 8 open drain digital outputs. Two of them (O6 and O7) can function as PWM outputs. Table 1 outlines the assignment of outputs to the GPIO. Each output is activated when its corresponding GPIO is set HIGH. The ENABLE signal is active-low. When ENABLE is set HIGH, all digital outputs are disabled.

Figure 1 shows recommended wiring for an LED (a) and relays (b, c) with open-drain outputs. Built-in diodes protect output transistors from transient voltage spikes (b). For long relay wiring, an external diode (c) is recommended.

digital-outputs

Fig. 1. Example digital outputs connections

Table 1. Digital outputs - GPIO

SIGNAL GPIO
ENABLE GPIO34
O1 GPIO35
O2 GPIO36
O3 GPIO37
O4 GPIO38
O5 GPIO39
O6 GPIO40
O7 GPIO41
O8 GPIO42

Table 2. Digital outputs parameters

PARAMETER VALUE
Quantity of outputs 8
Maximum current 500 mA
Maximum voltage 28 V DC

Software

Bash

Change state of output O1:

$ echo "34" > /sys/class/gpio/export  #export GPIOs to userspace 
$ echo "35" > /sys/class/gpio/export

#Set GPIOs as an output 
$ echo "out" > /sys/class/gpio/gpio34/direction 
$ echo "out" > /sys/class/gpio/gpio35/direction

#ENABLE active 
$ echo "0" > /sys/class/gpio/gpio34/value

#Turn on O1 
$ echo "1" > /sys/class/gpio/gpio35/value

#Turn off O1 
$ echo "0" > /sys/class/gpio/gpio35/value

#unexports GPIOs 
$ echo "34" > /sys/class/gpio/unexport 
$ echo "35" > /sys/class/gpio/unexport

The WiringPi library is pre-installed and provides tools for GPIO management. Below are some examples:

#Set GPIOs as an output 
$ gpio mode 34 out 
$ gpio mode 35 out

#ENABLE active 
$ gpio write 34 0

#Turn on O1 
$ gpio write 35 1

#Turn off O1 
$ gpio write 35 0

#Set O6 mode to PWM 
$ gpio mode 40 pwm

#Set PWM value for O6 to 500 (range: 0-1023)
$ gpio pwm 40 500

Python

To change the state of output O1, you can use the following commands:

$ python

>>> import RPi.GPIO as GPIO 
>>> GPIO.setmode(GPIO.BCM) 
>>> GPIO.setup(34, GPIO.OUT) 
>>> GPIO.setup(35, GPIO.OUT) 
>>> GPIO.output(34, False) # Activate outputs (ENABLE active-low)
>>> GPIO.output(35, True) #Turn on O1 
>>> GPIO.output(35, False) #Turn off O1