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Raspberry Pi PLC 38R review

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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.

The left side of the PLC 38R features six more relay connections, opto-isolated analogue/digital inputs,
and dip switches

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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.

The front of the unit features status LEDs, an extra Ethernet port, and access to Raspberry Pi 4’s power and micro-HDMI ports, plus 3.5mm AV jack

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 top of the robust housing includes technical information; the rear of the unit can be mounted on a DIN rail

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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

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