CAN Bus Transceiver

Introduction

Controller Area Network (CAN) is a communications protocol introduced initially for the automotive industry, but with wide use for any application which requires message based communication.  At a physical level CAN messsages are sent over a differential line and at a protocol level contain an arbitration ID for message identification and priority and a set of data, usually up to 8 bytes.  

CAN networks require transceivers to decode messages and split them into two digital signals for transmitting and receieving messages.  The device connected to the transceiver can then perform the logic required to decode and send messages.  CAN is fault tollerant and supports data transfer rates up to 1 megabaud.  

You can use our CAN bus transeier design to connect a number of devices to a CAN network, for example to connect a Raspberry Pi to your car's internal CAN network.  From there you can parse CAN messages normally.

Technical Details

There are many CAN transceiver ICs offered currently.  We have chosen the ADM3052 because it comes in a convenient SOIC package and is completely isolated.  Isolation is key, since any transients or short circuits will damage the expensive devices listening for messages without it.  For this reason, the ADM3052 requires separate ground connections and voltage supplies for the logic and bus sides respectively.  Other than that, the device is functionally simple and supports our data rate of 500 kilobaud, limited by devices attached to our bus.

CAN networks require termination resistors to prevent reflections in the bus and to bring the nominal voltage between the differential lines to 0V.  We include a footprint for this termination resistor, usually 120Ω, for when the transeiver is the last device in the bus.  This resistor must be appropriately rated, as CAN busses can potentially be driven with a large amount of energy.  0.75W is suggested.  The device requires a 12 or 24V and 3V3 supply.   It also requires a number of external components: a 300Ω 0.75W resistor on V+R and decoupling capacitors on the power pins.

The completed board is a simple 2 layer design.  It contains Molex connectors for connection to our main vehicle loom and test points for debugging.  It is small to facilitate mounting in enclosed locations. 

Additional Information

You can find additional information about our pod and the Hyperloop competition at https://www.michiganhyperloop.com/ or our instagram, @michiganhyperloop.