We need to be able to make a com (serial) connection remotely off site from PLC type device.
We have completed a POC for sending some signals to Azure IoT utilizing a Siemens IoT2020 running linux with a NB cellular modem on the Cat-M1 network. The reason for the NB cellular is due to signal strength in some sites as most locations don’t have network infrastructure in place. The main goal was to achieve an out of service signal and switch a couple of relays remotely which we achieved with both data and via sms.
As ideally (security by obscurity) and practically these modems are on the carriers private IP range although we can look at ipv6 if required.
We connected to a 5V modem port on the controller with a couple of cheap serial adapters however only received rubbish most of the time and at a set baud rate presume that we would have needed to use control lines and a handshake. We also presume that they are likely using proprietary communication.
We have software that can connect and run the PLC from a RJ45 connection on the controller to a hand held terminal device. The RJ45 can also connect to a Bluetooth device that then shares the com port to either an App on a smart phone or Windows computer. It has the option on Windows to connect to a com port and mentions RS232, Com port and Baud rate. There is also an option to connect by IP Address and com port.
Is there a practical way to do serial over cellular on IoT like devices using embedded Linux or similar?
Most research shows a lot of off the shelf units and dev boards are geared up to forward over ethernet, or to connect with a local Windows PC and then forward the virtual com port. We need to do both the connection with Azure IoT and forward the com port.