RS485 Pi

The RS485 Pi is a communication board supporting the RS-485 serial protocol.

Features

• RS-485 Half Duplex Port.
• Up to 250 kbps transfer rate.
• Use the Raspberry Pi to control external RS-485 devices.
• Stackable with other Raspberry Pi accessory boards.
• Mounting holes for use with the AB Electronics UK mounting kits (sold separately)

The RS-485 port is connected to the UART port on the Raspberry Pi using a SN65HVD72 interface. The SN65HVD72 IC converts the 3.3V UART signals to RS-485 voltages allowing communication with RS-485 compatible devices over a DB9 serial cable or twisted pair cable. The RS-485 port can be accessed through the DB9 port or the solder points on the PCB.

The RS485 Pi contains protection against voltage spikes in the form of a TVS Diode and two 10-Ω, Pulse-Proof Thick-Film Resistors.

Please note that you can only use one RS485 Pi board on a Raspberry Pi. if stacking with other boards we recommend putting the RS485 Pi at the top of the stack due to the height of the DB9 connector.

A 120-Ω resistor is included with the RS485 Pi which will need to be fitted if the board is connected to the end of the RS-485 bus.  The diagram below shows a typical network of RS-485 devices.

Assembly

The RS485 Pi is supplied with the 40 pin GPIO connector and the DB9 connector unsoldered.  

A 120R terminator resistor is included in the kit. This will be required if the RS485 Pi is used as an end node within an RS485 network.

Before using the RS485 Pi you will need to solder both connectors onto the PCB.  We suggest soldering the 40 pin GPIO connector first and then the DB9 connector.