MaixCAM MaixPy Using GPIO

Introduction

Using GPIOs allows you to control a pin to output a high or low voltage level or to read a signal from it. This is a very common way to read signals or output control signals.

Note: The pins on the MaixCAM are 3.3V tolerant. Do not apply 5V to them.

Prerequisites

Please learn how to use the pinmap module to set pin functions first.

To enable a pin for GPIO functionality, first use pinmap to set the function of the corresponding pin to GPIO.

Choosing the Right GPIO to Use

First, you need to know which pins on your device are available as GPIOs, as shown in the figure:

Device Model	Pinout Diagram	Pin Multiplexing Description
MaixCAM		The silkscreen on the board, e.g., `A19`, is the pin name, and `GPIOA19/PWM7` is the function name
MaixCAM-Pro		The first name, e.g., `A19`, is the pin name, and `GPIOA19/PWM7` is the corresponding function name
MaixCAM2		The first name, e.g., `IO0_A2`, is the pin name, and `GPIO0_A2/SPI1_CS0` is the corresponding function name

Note that pins may have other default uses. It's best to avoid these pins. Please refer to the pinmap documentation for details.

Circuit Considerations

Be aware that the voltage tolerance and load capacity of the pins are limited. You need to be careful when designing circuits to avoid basic mistakes, like asking "why can't the pin directly power a motor?"

Pin Voltage Tolerance: Unless otherwise specified, the pins operate at 3.3v. Do not connect an external 5v voltage.
Pin Input/Output Current: The input/output current of the chip pins is limited. They are generally only used for control signals. For devices with high current requirements, please use a conversion circuit.

Example: To control an LED, a simple circuit is as follows:
The LED is directly powered by a high-level output from the pin. This is the most intuitive way to use it, but you must be very careful. The maximum output and input current of a chip pin (the driving capability) is limited and is usually described in the chip's datasheet.
Here, the current is 3.3v/(LED+resistor resistance) < 0.64mA, so it can be driven directly. However, if your circuit's current is too high, it may fail to drive the device or even cause the chip to malfunction.

The correct approach is to connect an external conversion circuit so the pin only acts as a control signal. This can be done using a transistor, optocoupler, or relay. This document won't go into details; please do your own research.

GPIO Output Mode

As shown in the LED circuit diagram, we only need to provide a high voltage level to the A14 (MaixCAM2 is IO0_A6) pin for the LED to turn on:

from maix import gpio, pinmap, time, sys, err

pin_name = "IO0_A6" if sys.device_id() == "maixcam2" else "A14"
gpio_name = "GPIO0_A6" if sys.device_id() == "maixcam2" else "GPIOA14"

err.check_raise(pinmap.set_pin_function(pin_name, gpio_name), "set pin failed")
led = gpio.GPIO(gpio_name, gpio.Mode.OUT)
led.value(0)

while 1:
    led.toggle()
    time.sleep_ms(500)

First, get the pin and function name based on the board model.
Use pinmap to set the pin's function to GPIO.
err.check_raise is used to check the return value of set_pin_function. If there's an error, it raises an exception to prevent mistakes.
Initialize the GPIO object and set it to output mode.
The output value is toggled every 0.5s, causing the LED to blink.

For more API information, please see the GPIO API documentation.

GPIO Input Mode

from maix import gpio, pinmap, time, err

err.check_raise(pinmap.set_pin_function("A19", "GPIOA19"), "set pin failed")
led = gpio.GPIO("GPIOA19", gpio.Mode.IN)

while 1:
    print(led.value())
    time.sleep_ms(1) # sleep to make cpu free

Using the Illumination LED on MaixCAM-Pro

Both MaixCAM / MaixCAM-Pro and MaixCAM2 have a small LED connected to pins A14 and IO0_A6.
Additionally, the MaixCAM-Pro and MaixCAM2 also have an onboard illumination LED connected to pins B3 and IO0_A25, respectively, which turns on with a high voltage and off with a low voltage:

from maix import gpio, pinmap, time, sys, err

pin_name = "IO1_A25" if sys.device_id() == "maixcam2" else "B3"
gpio_name = "GPIO1_A25" if sys.device_id() == "maixcam2" else "GPIOB3"

err.check_raise(pinmap.set_pin_function(pin_name, gpio_name), "set pin failed")
led = gpio.GPIO(gpio_name, gpio.Mode.OUT)
led.value(0)

while 1:
    led.toggle()
    time.sleep_ms(500)

More Examples

See MaixPy examples.

API Documentation

For more API information, see the GPIO API documentation.

PINMAP

Key