I have a Raspberry Pi  which is located in a remote place. The only communication methods can be established  is to use 4G LTE cellular networks with no static IP address provided. Can I reach my Raspberry Pi from my computer or from my smartphone, also assuming both devices don’t have static IP addresses ?  Absolutely. As long as there is a SSH server which has a static IP address that  can be accessed from both sides, I can retrieve or send data from my computer to Raspberry Pi.

Raspberry Pi needs to establish a route using reverse tunnel or known as a remote forwarding. It routes a traffic to local machine which in this case is “my computer” or other destinations. Since my computer doesn’t have a static IP address, the traffic can be routed to SSH server which has a static IP address.

For all connections here, we use private and public keys so we will not be required to enter password everytime we connect to the server.

SSH Reverse Tunnel or Remote Forwarding.

On Raspberry pi we will enter the following:

ssh -v -i /home/pi/serverkey -R 5112:localhost:22 -p 22 myaccount@107.175.72.199

My user id on ssh server is myaccount. For connecting to the server , it has a port 22 for ssh and an IP address 107.175.72.199. Serverkey which is stored in directory /home/pi  is a private key which has to match a ssh server public key.

Here is the important part:

-R 5112:localhost:22

-R means remote forwarding. It will route port 22 on Raspberry pi to destination port 5112 which is located on ssh server.

-i identify file.

-v verbose.

SSH Tunnel or Local Forwarding.

On my computer which has own a ssh server , I can access destination port 5112 that will route the traffic to Raspberry Pi port 22 using following command:

ssh -v -i /home/mycomputer/serverkey -L 5112:localhost:22 -p 22 myaccount@107.175.72.199

I can also connect the Raspberry Pi using my phone with a SSH client installed.

After connection established and able to login to 107.175.72.199 server, the last step is to login to Raspberry SSH terminal:

ssh -i pikey -p 5112 pi@localhost

pikey is  an identity file for a private key that must match Raspberry pi public key.

 

 

 

 

 

 

When we signed unlimited data plans from wireless carriers such as T-Mobile, AT&T etc , it is by no means that we will  get unlimited bandwidth from those plans. We know we can use our cellphones for hotspot tethering but those carriers will slowdown the data speeds and will throttle the bandwidth significantly.

Some of  methods to avoid tethering detection is by changing  TTL (Time To Live) values ,or rooting the phone.

Here I will show another trick to avoid tethering data slowdown by using 4G LTE hat on Raspberry Pi 3B.

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TOOLS:

1. Rapsberry Pi 3B.

2. 4G LTE hat from Sixfab.  Quectel EC25 module using ECM mode is used here.

3. SSH Client (Termium or other SSH program/apps).

4. Web browser client which has proxy settings , for this setup we will use  Firefox web browser.

STEPS:

1.Settings up Raspberry Pi 3B as an Access Point using bridge mode.

https://docs.sixfab.com/page/setting-up-a-raspberry-pi-as-an-lte-hotspot

After following the step above you will have several files which works together to  create a bridge  between wlan0 and usb0. I have modified mine that let users to access eth0 using ethernet cable. Most likely you will have different files compared to mine.

These files are installed on my Raspberry Pi running on Debian Buster.

 

 

2.Internet connection settings.

https://docs.sixfab.com/page/internet-connection-with-quectel-ec25-by-using-ecm-mode

3.After doing all steps above, verify that the bridge networks appear on terminal screen  by typing “ifconfig”. It will looks like something like this:

Your bridge IP address probably look different.

4.Check your internet connection.

If yours is showing timeout or unable to reach  ,you need to check back step 2.

5.Install SSH client on your laptop/desktop or smartphones.  I use Termius as an SSH client on my laptop.

On my laptop I connect my wifi to “tapbridge”. That is ssid name on /etc/hostapd/hostapd.conf. You can create or change with different ssid name  and different password. If you are unable to connect to Rapsberry Pi , verify your first step (step 1), make sure you got the right configurations.

6.Create  a new host on Termius. My host address “192.168.225.55”, in case of yours, type “ipconfig” to see your bridge IP address.

Address: 192.168.225.55

General : “LTE wlan0 “, it is the name I created  to use together with Port Forwarding settings.

SSH on port 22.

credentials:

login: pi ( use yours , or it will be the same for default Raspberry Pi)

password: (your own raspberry Pi password) . Instead of password I use SSH-key so it will connect the Raspberry without entering password every time I need to login.

7.Create a new Forwarding on Termius.

Select the port forwarding type: Dynamic.

Dynamic port forwarding turn Termius into a SOCKS proxy server.

Label: cellular_sock ( create your own)

Local port number: 7777 ( you can choose any unused port number or uncommon port number), we will use this number for web proxy settings.

Bind address: 127.0.0.1

Intermediate host: LTE wlano ( it must match host name settings above).

8.Firefox web browser proxy settings.

Go to “settings” and “Network settings”. choose “Manual proxy configuration”.

SOCKS Host: localhost , Port:7777

choose :SOCKS v5. and press “OK” to save it.

9.Connect to 4G LTE with SOCK -5 configuration.

On Termius , go to “host’ and  click on “LTE wlan0”. this SSH will connect to Raspberry Pi. To get port forwarding running , go to “Port Forwarding” and click on “cellular_sock”. These chain connection will fire the SOCK proxy and you will able to browse Internet without tethering limitation.

Before without proxy  and After proxy data speed testings:

 

 

 

Missing some tags on Kepware server in which the operators could not operated or saw the valve status on SCADA screen.

We can turn Raspberry pi 3 as  AP(Access point) and can be utilized with wireless devices to scan PLCs or field devices network.

Requirements:

1.Raspberry pi 3

2.Power Supply (for Raspberry)

3.Wireless device ( tablet, laptop, or cellphone)

4.Ethernet cable

Keep in the mind that the following procedure is for Raspberry Pi 3 (Jessie raspbian)  which I am quite sure it might work for some  older versions with slightly modifications. I got the script from several sources online and I did modification to work on  PLC network that use static IP addresses.

1.Install hostapd, udhcpd and iptables

 

2. Create back up for these files, in case of installation failed.

 

3.Build the following  script (mywifi.sh).

Basically this script is to create several configuration (conf) files and will load them into default ones. DHCP (Dynamic Host Configuration Protocol)  configuration will give away the dynamic  IP addresses between 192.168.42.2 and 192.168.42.20 to your wireless devices and to access wlan0  meanwhile it will give a static IP address for raspberry pi: 192.168.42.1  . For older version , it is necessary to setup configuration on /etc/network/interfaces for interfacing with network (wlan0,eth0, etc )  but on newest Jessie installation, the network configuration is located on /etc/dhcpcd.conf . HostAPD configuration will create hotspot and APN ( Access Point Name). The next is NAT (Network Address Translation ) which works as a translator between external router that connect to eth0 and WIFI guests who access  wlan0.    :

 

4.Create AP.sh script

 

Run mywifi.sh and AP.sh

 

If there is no errors , you should able to see SSID name “WifiPLC” on your wireless devices under WIFI setting menu. Login and when ask the password, type “My_Passphrase”  that will save and connect it to your wireless devices. To test it, connect eth0 (ethernet port) on Raspberry Pi  to DHCP router that connect to Internet. The router will assign a dynamic IP address . Now you are able to connect to Internet. Type “www.google.com” on your phone browser to verify it.

This is last step if you need a static IP  and skip it if  you just need dynamic IP address . Eth0  still has a dynamic IP address and will not communicate with PLC static IP address network. Identify gateway address and check all existing PLC IP address and find a static IP address for Raspberry PI that will not cause conflicts with other numbers. In this example the gateway is 192.168.1.1 and the number has not been used by other PLCs is 192.168.1.50. To activate a static IP address, add the following to the very bottom of /etc/dhcpcd.conf file.

 

Save it as  /etc/dhcpcd.conf.

Reboot your Raspberry Pi , connect Ethernet port to  a PLC  router. Now if you have PLC CPUs  or Ethernet  modules  which have  “192.168.1.xx ” , type those number on your browser. Let says “192.168.1.33”. Most new Field devices or PLCs  have HTTP protocol capability on port 80/8080, so you will  see something like this  :

Using Raspbian shell terminal, we can find MAC number using “arp’ command,  install “nmap” utility to explore and troubleshoot  the network such as scanning particular IP address blocks, checking open/closed ports etc.

Process or manufacturing plants have PLCs which get signal inputs from mechanical buttons, switches, limit switches and send signal outputs to activate relays, solenoid valves etc.  In many cases, they use 24V DC power supply for PLC CPUs  and their I/O modules.  This voltage level is used for input modules and deliver 24VDC  from output module  to turn  solenoid valves, coils etc.

For non-critical use  and ignoring  the latency  , we can build  simple 5V to 24V DC I/O adapter that can be used with our Microcontrollers to drive 24V DC rating relays and  supplying  switches/buttons.

 

Don’t get confused with the schematic above . Yes, it works !. The reason there are two “opto couplers”  above ( Actually only one opto coupler with two sockets which I will explain later)  is that we can use GPIO from our Microcontrollers,  AVRs, Arduino boards etc  like we intended. For example we can use Pin 1 as input OR as  output  from the same block diagram above. Let says we have 8 I/O pins, each pin will go to both red and green block  so we just need to focus on our code/program without worrying which one is for input or output.

HOW IT WORKS:

(See the picture) The main part here is 4N29 opto coupler that can “convert”  either 5V DC to 24V DC or from 24V DC to 5V DC. The red square on the picture is a 4N29 socket  for output ,and the green one is a socket for input.  We have two sockets but we only need one opto coupler IC . When output signal needed , move this  IC to the red socket, otherwise we just leave it on green socket. Never put  two ICs on both sockets at same time to avoid input/output conflicts. The inputs/output devices will be connected to  blue square terminal block. Put the relays, bulbs, solenoids, switches,  and buttons there .

In the old days, We used to have electronic controllers or PLCs to send the warnings or alarms on the panel by turning combination of  light indicators  on or off. To understand these signals we have to refer their operation manuals to interpret these messages. For example if they have three indicators on the panel which has Light A(LA), Light B(LB) and Light C(LC),  it will be 2^3 =8 combinations of warning/alarms. To make it easy to understand , they provide us a troubleshooting table to tell operators or technicians to trace the problem. Continue reading Convert legacy control panel into LCD alarm and warning system with Arduino.