Strato Pi CM v3

A high quality and stable power supply is extremely important to ensure reliable operation of your Raspberry Pi for continuous 24/7 loads in harsh industrial environments.

Strato Pi CM accepts a wide power supply range and is able to effectively handle substantial amounts of ripple, noise and supply voltage fluctuations. The power supply stage is a heavily protected and filtered circuit, using oversized electrolytic capacitors, diodes and inductors, and a high efficiency voltage regulator.

The step-down converter is based on advanced, high-output-current PWM converter integrated circuits with low resistance MOSFET, with approximately 95% efficiency and up to 1.9A continuous output current (3A peak). It includes over current limiting, over voltage protection and thermal shutdown.

The power supply stage is also protected from reverse polarity with resettable fuses. Surge protection up to ±500V/2ohms 1.2/50μs ensures reliability in harsh environments.

The Raspberry Pi relies on Internet time servers to set its internal clock to the current date and time on start-up. If your applications always requires the correct time, even when not connected to the Internet, then you need to have a local real time clock/calendar to permanently keep track of time, even when the Raspberry Pi is off.

Strato Pi CM 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 PCF2131 general purpose RTCC chip from NXP. 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 Strato Pi CM is always powered, the battery should last well over 10 years.

RS-485 serial ports are widely used to connect devices in industrial automation and other applications. The Raspberry Pi lacks the circuitry to implement these protocols. While many USB adapters are available at reasonable price, they are usually not heavily protected and isolated.

The interface circuits of the RS-485 serial ports on Strato Pi CM are insulated from the power supply voltages, thus avoiding possible failures due to ground loops.

The insulation is obtained by means of a high efficiency isolated DC-DC converter and three hi-speed opto-couplers.

A micro-controller automatically manages the data direction of RS-485, taking into account the baud rate and the number of bits, without any special configuration. The Raspberry board can therefore communicate through its TX/RX lines without any other additional signal.

A hardware watchdog is an electronic circuit that can reset the processor if, for any reason, the software application appears to be stuck. An automatic hardware restart after a software hang can save your day, particularly on unattended applications that need to work continuously.

Taking advantage of the Strato Pi CM on-board micro-controller, we have implemented a hardware watchdog circuit that can be used, upon a software hang, to reset the Raspberry Pi CM.

The Strato Pi watchdog is completely independent from the Raspberry Pi’s internal CPU watchdog circuit and, being controlled by Raspberry Pi’s GPIO pins, it is extremely easy to control from your application and very effective in recovering from unexpected malfunction.