This simple power board is used in conjunction with the rotary-controller board. It provides a reliable power source for the Raspberry Pi and additionally it includes an RS485 interface chip which allows easy communication with any external RS485 device.
The UART to RS485 converter chip is powered by the 3.3v generated by the Raspberry. A few convenient LEDs provide some status information about the power supplies and the communication activity detected on the RS485 TX line coming from the SBC.
When powering up the board without an SBC connected to it, only the 5V status LED will power up.
This power board should be able to provide enough power for the SBC, a display, and a few external devices.
The board can be powered with an AC/DC power supply, making it easy to use with an old school transformer (24VAC max recommended) or any DC power supply (10-36V recommended).
Efficiency and absolute maximum ratins will vary depending on the provided power supply voltage, the selected coil is most efficient when working around 12-18 volts.
When powering the board with a DC power supply, polarity is not relevant, making it harder to make mistakes.
Some basic circuit protection is provided by means of ESD diodes and a resettable fuse.
The selected SR485 interface chip is compatible with 3V3 signals (same as the SBC) and it includes ESD protection, making it a simple choice for interfacing with external devices without many extra components.
When connecting the serial line with long distance wires make sure to properly select a termination resistor in your line and ensure also that proper biasing resistors are placed in order to maximize compatibility with 3rd party serial devices. 330 Ohm resistors are commonly used for line biasing, whereas 120 Ohm are generally used for line termination.
Propoer component selection, especially when dealing with long distances, together with suitable cable selection, are critical for a reliable and fast connection between your devices.
The project includes also suitable production files that are currently being used for manufacturing, if you see mistakes or have ideas that you want to suggest for this project, shoot me an email: bartei81@gmail.com.
Thanks for your interest in the project!