While the company also produces PLCs based on Arduino and ESP32 microcontrollers, the model reviewed here is one of the Raspberry Pi-based range and therefore benefits from superior processing power – an advantage when handling multiple real-time processes – and the ability to run a full Linux operating system, the familiar Raspberry Pi OS, by default. You can connect the unit to a monitor via HDMI if needed, but in most cases operators will SSH in from another computer.
Raspberry Pi power
The PLC 38R model is based around a standard Raspberry Pi 4 (with 2GB, 4GB, or 8GB RAM), with the optional addition of up to two extra communications boards such as 4G cellular and LoRA. Naturally, Wi-Fi and Bluetooth are built-in, thanks to Raspberry Pi 4, along with dual Ethernet ports (the board’s built-in port plus an extra one).
Raspberry Pi 4 is secreted inside a robust plastic case with a large metal heatsink on the base. The whole unit weighs 711g and is mountable on a DIN rail. The ambient operating temperature is 0 to 50°C, with a humidity level of 10 to 90%, while the case has a shockproof resistance of 80m/s2 in the X, Y, and Z axes.
Cutouts in the case provide access to Raspberry Pi 4’s USB and Ethernet ports on one side and – in a recess – micro-HDMI ports and the USB-C power port. You can’t power the whole unit that way, however: instead you’ll need to connect a 12–24V DC supply via two screw terminals, making sure the polarity is correct. Industrial Shields offers a suitable DIN rail power supply for €25.
To protect the electronics and avoid data corruption during sudden voltage drops in the event of a power outage, the PLC 38R has an integrated UPS shield. When the UPS kicks in, the outputs maintain their last activation state until the unit is rebooted. A real-time clock is also included, powered by a button battery – easily replaceable by removing a plastic panel. Insulation resistance is provided to the tune of 20mΩ at 500VDC between the AC terminals and protective earth terminal. Dialectic strength is rated as 2300 VAC at 50/60Hz for one minute with a maximum leakage current of 10mA.
Pinned to the ground
The most important feature of any PLC is its range of I/Os. Raspberry Pi PLC 38R is absolutely loaded with them, divided into zones and connectable via removable screw terminal blocks. On the right-hand side of the unit are sets of analogue (0 to 10V) and digital/PWM outputs. Underneath, there’s a long row of I/O and power/ground pins covering standard protocols such as SPI, I2C, and RS485, plus a couple of direct GPIO pin connections.
The remainder of that side is taken up by ten sets of relay switch connections. Another six are found on the left side of the unit, along with opto-isolator protected digital/analogue inputs, configurable by two sets of four dip switches. Note that other Raspberry Pi PLC models feature varying numbers of I/Os and relays, so you can choose the one that best suits your requirements.
The downloadable documentation is fairly detailed and features examples of how to use pre-installed Bash scripts to read various inputs, and trigger outputs and relays, so it’s fairly easy to get started.
Verdict
9/10
Protected by a robust case, this PLC is packed with I/Os and relays, making it suitable for a wide variety of industrial applications.
Specs
Processing: Raspberry Pi 4 with 2GB, 4GB, or 8GB RAM
I/O: 8 × analogue/digital opto-isolated inputs (5-24V), 4 × digital opto-isolated inputs, 16 × relay outputs, 6 × analogue outputs (0-10V), 6 × digital/PWM outputs, I2C, SPI, RS485, RS232/TT
