A Raspberry Pi based PLC
Iono Pi is an extremely versatile Input/Output module which combines several digital and analog input lines, support for standard interfaces like 1-Wire and Wiegand and power relay outputs, typical of a modern PLC, with the incredibly powerful quad-core processor of the Raspberry Pi 3 or 4.
Iono Pi adds other important features that are essential to use the Raspberry Pi for professional applications, like a robust power supply with wide voltage range (9-28V) capable of up to 4A output current at 5V, and a real time clock with lithium back-up battery.
Iono Pi can be used for an incredible range of applications, from data acquisition and control, to home and building automation, as well as access control, hotel room control solutions, environmental monitoring and many many others. And software development is pure Raspberry Pi, with the constantly growing list of standard and proprietary software frameworks available on this platform.
Iono Pi can be employed both in industrial and residential environments, for professional applications where extreme reliability, ruggedness and compliance with technical and safety directives are required.
It is compliant with the low voltage and EMC CE directives, as well as the harmonised standards for electromagnetic compatibility, electrical safety, emission and the RoHS directive for hazardous substances. It is also compliant with the applicable FCC rules and IC standards.
- 4 modules DIN rail case
- power supply and I/O connections on screw terminal block
- 9÷28Vdc power supply, with surge and reverse polarity protection, and 2.2A resettable fuse
- up to 4.0A max current to the 5V Raspberry Pi power supply input pins (at 24Vdc)
- 4 x power relay outputs rated for 6A at 250V
- 2 x analog voltage inputs 0÷30V
- 2 x analog voltage inputs 0÷3V on internal pin-headers
- 7 x configurable digital input/output pins, for potential-free or voltage inputs, TLL input/outputs and open collector outputs
- 1-Wire and Wiegand support
High reliability and security:
- real time clock (RTC) with replaceable back-up battery
- embedded Microchip ATECC608A secure element chip
- optional pre-assembled SPBF10X Strato Pi Fan active cooling temperature controlled high performance fan
- GPIO-controlled LED
- power-on status LED
Raspberry Pi embedded:
- 1 x Ethernet
- 4 x USB
- 1 x HDMI (RPi 3+) / 2x Micro HDMI (RPi 4)
- 1 x microSD card slot
- 1 x jack for audio and composite video
The power supply stage is a heavily protected and filtered circuit, using oversized electrolytic capacitors, diodes and inductors, and a high efficiency, high power voltage regulator, capable of delivering up to 4A current at 5V. Iono Pi accepts a wide power supply range, from 9 to 28 Vdc, and is able to effectively handle substantial amounts of ripple, noise and supply voltage fluctuations.
Iono Pi has 4 power relay outputs with normally open contacts, rated for 6A at 250V, which can tolerate peak currents (inrush current) up to 15A.
These relays have a minimum mechanical durability of 5,000,000 operations.
The relays are controlled by 4 GPIO output pins of the Raspberry Pi, so they are very easy to control from any software development environment or application.
The relays ensure 5kV insulation between coil and contacts (1.2/50 μs voltage wave), protecting the Iono Pi circuitry and the Raspberry Pi from external surge.
Iono Pi has two dedicated analog inputs on the low voltage terminal block. The voltage input range is 0-30V. We use the MCP3204 4-channel 12-Bit A/D converter from Microchip to convert the analog voltage to digital. The converter is connected to the Raspberry Pi via the SPI serial interface. The 12-Bit A/D converter offers good resolution and sampling speed.
The two additional inputs of the A/D converter are available on an internal header for custom extensions. These inputs don’t have a voltage divider before the converter’s inputs, and accept a voltage range of 0-3V.
Up to 6 pins can be used as digital inputs, and are wired, through a protection network, to 6 GPIO pins of the Raspberry Pi. Applying a positive voltage (up to 40Vdc) to these pins will bring the corresponding GPIO pin to high. Three of the digital input pins are shared with open collector outputs, while the remaining three can be reconfigured as TTL I/O lines.
All inputs are protected by a network of resistors and Schottky barrier diodes to ensure that the input pins of the Raspberry Pi never receive voltages significantly higher than 3V or lower than 0V.
Open Collector Outputs
Three of the Raspberry Pi’s GPIO pins are connected to discrete open collector drivers with a maximum output current of 100mA. These outputs are individually protected against over-current and short circuits.
When the over-current protection is triggered, the output will open, stopping the current flow. A simple reset to 0 of the Raspberry Pi’s GPIO pin will reset the protection.
TTL I/Os – Wiegand – 1-Wire
Up to 4 terminal pins can be used as bidirectional TTL I/O lines (0-5V), connected to the Raspberry Pi GPIO pins through a bidirectional level shifter.
These lines are suitable for interfacing with up to four 1-Wire buses, up to two Wiegand devices, or many other digital protocols.
Real Time Clock
Iono Pi features a battery-backed real time clock/calendar, directly connected to the Raspberry board through the I2C bus interface. The automatic switch-over to a lithium battery guarantees the functionality of the RTC when its main power supply fails.
The real time clock is based on the MCP79410 general purpose RTCC chip from Microchip. It is connected to the Raspberry Pi’s I2C bus and, besides the standard clock function, it has several other advanced features.
A replaceable CR1025 battery is used as a backup power source when the main power is not available. If Iono Pi is always powered, the battery should last well over 10 years.