Introduction

This "Project Guide" is written to show some of the capabilites of NavQ. In conjunction with a Teensy LC and a strip of WS2812B LEDs, you can add a forward-facing battery indicator light to your drone.

Prerequisites

Software

The software needed to run this project on your NavQ is as follows:

1. ROS Noetic

2. MAVROS

You can install this software using the guides here:

Hardware

The hardware needed is the same as the hardware from the I2C guide here:

Code

At the moment, we're just going to paste the code here, and a more detailed guide will be written later.

Teensy code

This code should be uploaded to the Teensy using the Arduino IDE.

NavQ code

The ROS node should be placed in the home folder ('/home/navq/')

The service file should be located in /etc/systemd/system/.

The Launch script should be located in /usr/local/bin/.

Making the ROS node run on boot

Once all of the necessary files are placed in their respective directories, you need to make the systemd service run at boot. To do this, run in the terminal:

Controlling PWM on NavQ

The PWM chips are tied to the onboard LED on NavQ. There are three PWM chips: pwmchip0, pwmchip1, and pwmchip2. Each of these "chips" have one PWM line attached to them: pwm0. To use these PWM lines, you will need to use the sysfs interface.

Using the sysfs interface to control the onboard LED

Step 1

Log into the root user on NavQ by running this command:

Step 2

Navigate to /sys/class/pwm and run the following commands:

Step 3

Now that our PWM lines are exported for each chip, we can change the duty cycle of the PWM lines and enable them. The default frequency is 2730667 Hz. For a 50% duty cycle, we will use half of this number: 1365333. Apply this duty cycle to each chip by running the following commands:

Step 4

We will now enable each line. The colors for each chip are as follows:

pwmchip0: RED

pwmchip1: GREEN

pwmchip2: BLUE

To enable the colors, run the following commands:

Running these commands in succession should enable the LEDs in a RED, GREEN, BLUE pattern until you reach a white LED.

Controlling the onboard LEDs programmatically

There are many communications interfaces supported on NavQ through the JST-GH connectors on the HoverGames Interposer Board. The page links below are guides for each one

SPI userspace driver

In the October Demo image, we have enabled SPI in the kernel to allow HoverGames participants to communicate with SPI devices. The October Demo image will be released soon.

Introduction

If you're thinking about using the CAN protocol on your drone, this guide will walk you through using our UCANS32K146 to create a CAN interface.

Since there isn't a native CAN bus on the NavQ, we can use a protocol called SLCAN to communicate CAN messages across a UART connection. We have built a binary for the UCANS32K146 that acts as an SLCAN transfer layer. This means that we can add a CAN bus to NavQ by just connecting the UCANS32K146 to the UART3 port.

Setting up SLCAN on NavQ

To enable SLCAN on NavQ, run these commands:

Now you can use SocketCAN or python-can to send and recieve CAN messages over the slcan0 interface. As an example, here is how to send a CAN message from the command line:

Flashing your UCANS32K146 with the SLCAN conversion binary

Follow the guide at the link below to flash the SLCAN binary to your UCAN board:

I2C Example

The NavQ includes an I2C port in one of the JST-GH connectors. You may use this port to communicate to other devices in your drone system. In this example, we will go over the process of connecting a Teensy LC to the NavQ over I2C to control some WS2812 LEDs.

TODO

1. Add guide for using C/Python SMBus libraries for controlling I2C

2. Add more pictures/visuals

3. Explain teensy code

Prerequisites

Hardware

1. Teensy LC

2. NeoPixel LED Strip (Ex. )

3. JST-GH connectors and pre-terminated wires

Software

1. Teensy side

   1. Arduino IDE

   2. TeensyDuino

Preparing the JST-GH connector

To create the I2C connector, you'll need to order some JST-GH hardware. Here is a link to a digikey page where you can purchase connectors:

And here is a page where you can purchase the jumpers:

In the hardware overview (link here: ), you can see the pinout for the I2C connector. Here is another screenshot of it:

The 5VP pin is on the left-most side of the connector, and GND is on the right-most side. I2C2_SDA is pin 4, and I2C2_SCL is pin 5. The JST-GH connector is positioned with the retention clip facing away from you when you are determining the left/right sides.

Wiring the Teensy

You'll need to do some soldering for the first step in this project. In the two pictures below, the NeoPixels are connected to the LED 5V, LED GND, and LED SIG pins. The JST-GH connector to the NavQ connects to the SDA/SCL pins and 5V + GND pads on the back of the Teensy.

One thing to keep in mind is that even though the Teensy LC does not include pullup resistors to 3.3v for the I2C lines, pullups are not required since the NavQ has internal 4.7k pullups on it's own I2C bus (on the SoM).

Pictures

Here are a couples images of this setup:

Teensy code

We have written some simple example code that changes the color of the NeoPixel LEDs when the Teensy recieves I2C data. In the example below, the slave address of the Teensy is 0x29, and the color of the LEDs change from green to white when a 0x1 byte is sent to the Teensy. If any other byte is sent to the Teensy, the color changes back to green.

NavQ commands

Add navq user to i2c group

To use the i2c commands without root, you'll need to add the navq user to the i2c group. To do this, you can run the following command:

Checking connection

Once your Teensy is connected using the I2C JST-GH connector, you need to confirm that the NavQ recognizes the Teensy as an I2C device. To do this, you can run the following command on the NavQ:

You should see a device at address 0x29. If there is no device at address 0x29, you'll need to check your wiring.

Sending data to the Teensy

To send data to the Teensy, you can use the following command:

This will change the LEDs to white. You can swap the 0x1 with a 0x0 or any other byte to switch back to green.

Controlling I2C bus with Python/C

Controlling the I2C bus with console commands is great, but what about when we want to integrate those commands into code? Well, with Python and C, we can control the Teensy over I2C by using some libraries supplied in both the Linux kernel and through pip.

Python

First, you'll need to install the smbus pip package. To do this, just run in your terminal:

Once that is installed, you can run a simple script to select a 1 or 0 to send to the NavQ to change the color of the LEDs.

The expected output of this script is as follows:

By selecting 1 or 0, you can change the color of the LEDs to white or green.

C

To control the I2C bus with C, you can use the following code:

Controlling GPIO through the command line

There are several GPIO pins on the various JST-GH connectors on NavQ. To control these GPIO pins, follow the instructions below.

Exporting GPIO pins

In order to use GPIO pins, we need to export them in Linux first. To do this, we need to know the GPIO number for the pin we want to access. We can compute this number using the following formula:

For example, if we want to access the GPIO1_IO12 pin on the UART4/I2C/GPIO connector, we would find that the GPIO number is:

If you want to find out what pins correspond to what GPIO numbers, we have tables in the Hardware Overview/Pinouts and Connector info section here:

Once you know the GPIO number of the pin you want to access, exporting the pin for use is easy. All you have to do is echo the pin number to /sys/class/gpio/export. For example, if we were to export GPIO1_IO12, we would run the following in our NavQ console:

Changing the pin direction

Next, we will want to change the direction of the GPIO pin for our specific use case. There are two options: in and out. To do this for GPIO1_IO12, you can run the following in your NavQ console:

Reading or Writing the GPIO pin value

To read or write a value to the GPIO pin, we will follow a similar process to changing the pin direction. A pseudo file named value is created at /sys/class/gpio/gpioXXX/value that holds a 1 or a 0. If you echoed out to the GPIO direction file, you can control the pin. To control the GPIO1_IO12 pin, just run the following in your NavQ console:

If you echoed in to the GPIO direction file, you can read the value file and find the current state of the pin. To do this for the GPIO1_IO12 pin, you can run the following in your NavQ console:

Controlling GPIO programmatically (in C)

Prerequisites

1. Create new group called gpio

2. Create new udev rules file

Create a file at /etc/udev/rules.d/99-gpio.rules and add the following to it:

This will allow you to access the GPIO pseudofiles without being root.

Source Code