Need a robust housing/motherboard for your Raspberry Pi Compute Module? Brian Corteil gives the Strato a spin
The Strato Pi CM (From £264 / $290) is a housing/motherboard designed for all versions of the Raspberry Pi Compute Module (CM) and is from a line of industrial products for the Pi/CM from Sfera Labs. The Strato Pi CM can be supplied with or without a Compute Module.
Designed for the IoT market, it enables a Raspberry Pi to interface with industrial equipment/sensors to the internet. Possible roles for the Strato include collecting sensor/diagnostics data, as a web interface to the collected data, to bridge old equipment via its RS‑485 port to the internet, and for a webcam CCTV network video recorder (NVR).
Opening the box, we found a standard two-gang DIN module that can be mounted to a DIN rail type normally used in electrical distribution boards and industrial control panels. The removable connector block is clearly labelled along with the LEDs on the front panel. On close inspection, the module has an RS-485 interface, two USB ports, and an Ethernet port. Other features include 9 to 28 V DC power voltage, a real-time clock, controllable LED, and a hidden push-button.
Obtaining access to the PCB proved very simple: you just need to remove the DIN rail retaining clip, power/RS-485 block and, using a small bladed screwdriver, the PCB is exposed. There are a couple of new interfaces: a micro USB port for programming the CM, and a microSD holder if you are using a CM Lite board and the hidden button.
Your reviewer handed the Strato to friendly electronic engineer and fellow Makespace member Rob Karpinski for his view of the construction and design. Having given it a once-over, he said that it was well made and that the RS-485 inputs were well protected. When told the cost of the unit, he choked a little but did say that it was expected for a device designed for industrial use.
Sfera Labs sent the Strato Pi CM Solo for review; this version does not come with a CM, but installing one is easy: just line it up and push down until it clicks. The next step is to install Raspbian. Reading the included Quick Reference, we were pointed to the user guide on the Sfera Labs website and then instructed to follow the guide on the Raspberry Pi site – magpi.cc/UtAcOj. We followed the guide and used the micro USB port; the user guide did not mention that the Strato had to be powered at the same time to install Raspbian Stretch Lite on the CM eMMC. We remembered to include a file called ssh to enable remote access and then connected to the Strato via its Ethernet port using PuTTY.
Following the user guide, we installed the Strato Pi utility and the software supporting the real-time clock. We played around with the utility, turning on/off the LED, and restarting the CM using the watchdog feature – although it turns out you don’t need to use the utility to access these features or the button.
After installing the GPIO Zero Python library, we wrote a simple script to flash the LED every couple of seconds for ever. This script has now been running for over 14 days; the Strato module has been sitting in your reviewer’s garden office / toy room, in temperatures over 35°C with no issues.
Next thing to test was the RS-485 serial port. Luckily, we had an RS-485 to RS-232 and a serial-to-USB converter in the test equipment box. Using PuTTY on the PC, we were able to access the CM’s console and use the command line as normal. With the correct cable, this means we could use the console or have sensors/equipment installed up to 1000 metres away.
The Strato Pi CM is for a niche market that requires the versatility of the Raspberry Pi in a small compact format that the Compute Module allows, and the professional user requires. The build quality is excellent and with a well-thought-out design. The inclusion of a real-time clock, isolated RS-485 serial interface, LED, and button, plus the wide range of voltages the Strato Pi can take for its power input, are its strengths. Adding all these functions to a standard Pi would require the use of several HATs stacked on top of each other. Your reviewer would personally like to see some GPIO pins broken out from the Compute Module with the same protection as the RS-485 port, to allow the adding of I2C, SPI devices, sensors, and extra LEDs and buttons.
If you need the power of the Raspberry Pi 3 Compute Module in a compact industrial case with an RS-485 interface, we don’t think you would go wrong with the Strato Pi CM.