Raspberry Pi Gadget Building

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We offer remote lessons on basic Raspberry Pi gadget building. Suppose you have a Raspberry Pi device, some other sensors and parts to connect to it, and need help to get started. This is where remote Raspberry Pi tutoring may help.

Raspbery Pi 3 model B with an SD card
Raspberry Pi 3

Example Raspberry Pi Lesson

In this example lesson we show how to connect a cellular module to a Pi and make it connect wirelessly over cellular network. This rig could later be used as a foundation for IOT gadgets.

Required Parts

We will use the following parts for this project:

Required parts for Raspberry Pi project
Required parts for Raspberry Pi example project

Starting with Raspberry Pi

We'll first try to get Raspberry Pi up and running. This should verify that that we have a working board and that the OS is properly installed. We do it by doing the following:

Raspberry Pi desktop after booting up
Raspberry Pi desktop after starting up

Connecting a Cellular Module to Raspberry Pi

Now let's connect our cellular module to Raspberry Pi. Our example setup occurs in Vancouver, British Columbia, Canada on Shaw Mobile network. For this to work we need have the following.

Name: Internet
APN: wsp.shaw.ca
Proxy: Not Set
Username: Not Set
Password: Not Set
Server: Not Set
MMSC: Not Set
MMS Proxy: Not Set
MMS Port: Not Set
MCC: 302
MNC: 490
Authentication type: Not Set

Name: MMS
APN: mms.shaw.ca
Proxy: Not Set
Username: Not Set
Password: Not Set
Server: Not Set
MMSC: http://mms.shaw.ca (iPhone Only)
MMS Proxy: 74.115.197.70
MMS Port: 8080
MCC: 302
MNC: 490
Authentication type: Not Set
APN Type: mms

Power Supply Considerations

Some resources on the Internet mention that you might need a 2A power supply for Pi and this hat to work together nicely. In this lesson we used a more powerful supply with connected USB breakout. Our power supply can display currently consumed current as displayed on the picture below.

Power supply with USB breakout for Raspberry Pi project
Power supply with USB breakout for Raspberry Pi project

In our experiments we never saw consumed current to go over 1A. However, the Pi itself still occasionally showed us a low voltage warning when 4G hat was connected via a single USB cable (no connection over GPIO pins). PS displayed a solid 5 volt output all the time. Why this happens and how to fix this is beyond the scope of this lesson.

Below is a picture of our rig with 2A USB power supply, which works just as good.

Raspberry Pi with 4G hat and 2A USB power supply
Raspberry Pi with 4G hat and 2A USB power supply

Connect the Antenna!

Make sure to connect the antenna to your 4G hat! Otherwise you may not be able to connect to your network. It is as simple as that. Save yourself hours of troubleshooting by connecting the antenna properly in the first place.

4G hat with connected antenna
4G hat with connected antenna

Inserting SIM Card into 4G Hat

For our cellular connectivity to work we have to insert a SIM card into a slot on the back of the cellular module. Here is how it looks with inserted SIM card:

4G hat with inserted SIM card
SIM7600A-H 4G hat for Raspberry Pi with inserted SIM card

Connecting Things Together

Now it's time to connect everything together. We need 2 USB to Micro USB cables. One goes from Raspberry Pi to our power supply breakout (black one on the pictures below). Another goes from a Raspberry Pi USB port to 4G hat (white one). Note that we don't use GPIO pins.

Raspberry Pi connected to 4G hat via a single USB cable
Raspberry Pi connected to 4G hat via a single USB cable
A bigger picture of Raspberry Pi connected to 4G hat
A bigger picture of Raspberry Pi connected to 4G hat

Turning 4G Hat On

There is a power on button on 4G hat identified as PWRKEY. Press, hold it for approximately 1 second, then release to turn the hat on. The NET LED comes on. If all is good it should become flashing after approximately 10 seconds.

Some documentation for the cellular module is here. Among other things, it says that if you want to let the module power on automatically after booting, you can connect PWR pin to GND and connect P7 pin to GND as illustrated by the following picture.

4G hat manufacturer picture for automatic turn on
4G hat manufacturer picture for automatic turn on
Raspberry Pi 4G hat wired for automatic turn on
4G hat wired for automatic turn on

Waveshare documentation also has the following on the NET LED status:

Always on: seacrhing network, call connect.
200 ms on, 200 ms off: data transmit, 4G registered.
800 ms on, 800 ms off: 2G/3G registered network.
Off: power off, sleep.

Which means we can determine if we are connected to 4G (faster) network rather than 2G/3G (slow) by how fast the LED is blinking, if at all.

4G Hat Setup

We used what is excellently covered in this resource to set up our hat. Detailed steps are below.

Updating Raspberry Pi

We first update our Raspberry Pi with the following commands:

sudo apt update -y
sudo apt dist-upgrade -y
sudo rpi-update

Reboot after all updates are applied.

sudo reboot

Enabling Serial Port Hardware

We have to enable serial port hardware for the Pi to communicate with our cellular module. Start raspi-config as so:

sudo raspi-config

Then select Interface Options followed by P6 Serial Port. Make sure that serial port hardware is enabled. Reboot if required.

Enabling UART on Raspberry Pi
Enabling UART on Raspberry Pi

I made a mistake of not enabling it in my initial experiments. I was able to establish connections as described below. However Internet connectivity was quickly being lost (within minutes). Serial port communication is required to keep it up. Do not repeat my mistake, enable serial port hardware.

Installing libqmi-utils and udhcpc

We will need libqmi-utils to communicate with a cellular module and udhcpc to acquire an IP address for Raspberry Pi from mobile network. We can install these packages using the following command:

sudo apt install libqmi-utils udhcpc

Using qmicli Commands to Communicate with 4G Hat

We can now run qmicli commands to talk with our 4G hat.

pi@raspberrypi:~ $ sudo qmicli -d /dev/cdc-wdm0 --nas-get-home-network
[/dev/cdc-wdm0] Successfully got home network:
    Home network:
        MCC: '302'
        MNC: '490'
        Description: 'Freedom'

The response above indicates a successful detection of a home network. We see that MCC and MNC values match with what Shaw Mobile provided us with.

There are many qmicli commands available. You can run this to see them all:

qmicli --help-all

Configuring the Module to use raw_ip Protocol

We can start using raw_ip protocol with the module by issuing the following commands:

sudo ip link set wwan0 down
echo 'Y' | sudo tee /sys/class/net/wwan0/qmi/raw_ip
sudo ip link set wwan0 up

Connecting to Cellular Network

We will now use the APN provided by ISP to connect to cellular network as so:

sudo qmicli -p -d /dev/cdc-wdm0 --device-open-net='net-raw-ip|net-no-qos-header' --wds-start-network="apn='wsp.shaw.ca',ip-type=4" --client-no-release-cid

If all goes well, the result could be something like below:

pi@raspberrypi:~ $ sudo qmicli -p -d /dev/cdc-wdm0 --device-open-net='net-raw-ip|net-no-qos-header' --wds-start-network="apn='wsp.shaw.ca',ip-type=4" --client-no-release-cid
[/dev/cdc-wdm0] Network started
    Packet data handle: '3785466208'
[/dev/cdc-wdm0] Client ID not released:
    Service: 'wds'
        CID: '20'

Obtaining IP Address for Raspberry Pi

We can use udhcpc to lease an IP address for our Raspberry Pi as so:

sudo udhcpc -i wwan0

A successful lease may look like the following:

pi@raspberrypi:~ $ sudo udhcpc -i wwan0
udhcpc: started, v1.30.1
No resolv.conf for interface wwan0.udhcpc
udhcpc: sending discover
udhcpc: sending select for 10.187.89.70
udhcpc: lease of 10.187.89.70 obtained, lease time 7200
Too few arguments.
Too few arguments.

We have now connected our Raspberry Pi to the Inernet using cellular network. We can ping outside hosts, browse the Internet, check emails, etc.

Automating Things at Boot

We can use the following shell script to automate bringing up cellular network after Raspberry Pi boot:

#!/bin/bash

echo 'starting...'
ip link set wwan0 down
echo 'Y' | tee /sys/class/net/wwan0/qmi/raw_ip
ip link set wwan0 up
echo 'trying to start network...'
qmicli -p -d /dev/cdc-wdm0 --device-open-net='net-raw-ip|net-no-qos-header' --wds-start-network="apn='wsp.shaw.ca',ip-type=4" --client-no-release-cid
echo 'sleeping 10 seconds'
sleep 10
echo 'about to call udhcpc'
udhcpc -i wwan0 -f -n -q
echo 'after a call to udhcpc'
ip a s wwan0
echo 'ending...'

And executing it 2 minutes after boot with the following crontab entry. This command assumes our is /home/pi/start_network.sh:

@reboot sleep 120 && sudo /home/pi/start_network.sh > /home/pi/start_network.log

Long term (overnight) experiments with this rig show us that cellular Internet connectivity occasionally disappears. Perhaps due to inactivity on sockets, or because of some other reason. Also, sometimes the qmicli command to start network fails for unknown reasons. We can fix this by rebooting our Pi every hour like so in crontab:

55 * * * * sudo reboot

The above cron entry reboots our Pi at 55 minutes every hour, therefore forcing it to reconnect. This means that if / when things go haywire, we may have a chance to recover connectivity in an hour. Here is how our crontab file looks like with both lines in:

@reboot sleep 120 && sudo /home/pi/start_network.sh > /home/pi/start_network.log
55 * * * * sudo reboot

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