Adafruit CAN Bus FeatherWing User guide

Adafruit CAN Bus FeatherWing

Created by Liz Clark

https://learn.adafruit.com/adafruit-can-bus-featherwing

Last updated on 2023-03-29 09:28:47 AM EDT

©Adafruit Industries Page 1 of 13

Table of Contents

Overview

Pinouts

• Terminal Block Pins

• Edge Launch DE-9 Connector Solder Pads

• Terminator Jumper

• Reset Pin and Jumper

• Chip Select Pin and Jumper

• Interrupt Pin and Jumper

• Silent Mode Pin

CircuitPython

• CircuitPython Microcontroller Wiring

• CircuitPython Usage

• Simple Test Example

• Testing with Two CAN Bus FeatherWings

Python Docs

Downloads

• Files

• Schematic and Fab Print

3

6

8

12

12

©Adafruit Industries Page 2 of 13

Overview

CAN Bus is a small-scale networking standard(), originally designed for cars and, yes,

busses, but is now used for many robotics or sensor networks that need better range

and addressing than I2C, and don't have the pins or computational ability to talk on

Ethernet. CAN is 2 wire differential, which means it's good for long distances and

noisy environments.

Messages are sent at about 1Mbps rate - you set the frequency for the bus and then

all 'joiners' must match it, and have an address before the packet so that each node

©Adafruit Industries Page 3 of 13

can listen in to messages just for it. New nodes can be attached easily because they

just need to connect to the two data lines anywhere in the shared net. Each CAN

devices sends messages whenever it wants, and thanks to some clever data

encoding, can detect if there's a message collision and retransmit later.

If you'd like to connect your Feather to a CAN Bus, the Adafruit CAN Bus FeatherWing

with MCP2515 controller and TJA1051/3 transceiver will work with any and all

Feathers! The controller used is the MCP2515, an extremely popular and well-

supported chipset() that has drivers in Arduino and CircuitPython() and only requires

an SPI port and two pins for chip-select and IRQ. Use it to send and receive messages

in either standard or extended format at up to 1 Mbps.

©Adafruit Industries Page 4 of 13

We've added a few nice extras to this Feather to make it useful in many common CAN

scenarios:

5V charge-pump voltage generator(), so even though you are running 3.3V on a

•

Feather board, it will generate a nice clean 5V as required by the transceiver.

3.5mm terminal block() that can be soldered in to get quick access to the High

•

and Low data lines as well as a ground pin.

120 ohm termination resistor on board, you can remove the termination easily by

•

cutting the jumper marked TERM on the top of the board.

A spot that one can solder an optional (not included!) edge-launch DE-9

•

connector() that is commonly used for connecting to CAN devices. L is

connected to pin 2 and H is connected to pin 7. You could then plug this into an

ODB-II cable to connect to a car's CAN network() - you'll still need software to

decode the messages though!

Pre-connected CS and INT pins on the two pins to the left of the I2C Feather

•

port - usually these are pins #5 and #6 but some feathers may have different

numbering! You can cut the bottom solder jumpers and use the breakout pads to

connect to any two IO pins you like.

Each order comes with an assembled 'Wing, terminal block and header. You will need

to solder in the header yourself but it's a quick task.

©Adafruit Industries Page 5 of 13

Pinouts

Terminal Block Pins

On the front left of the board, are the three pins for the included terminal block. It is

outlined in white on the silk.

CANL - the CAN low signal for the CAN Bus standard.

•

- - common ground shared between the two CAN connections

•

CANH - the CAN high signal for the CAN Bus standard.

•

Both CANL and CANH are connected to a 5V charge-pump voltage generator(). Even

if you are using 3.3V logic on a Feather board, it will generate a nice clean 5V as

required by the CAN Bus transceiver.

©Adafruit Industries Page 6 of 13

Edge Launch DE-9 Connector Solder Pads

On the front-right end of the board are the solder pads for attaching an optional edge

launch DE-9 connector(). This is commonly used for connecting to CAN devices. CAN

L is connected to DE-9 pin 2 and CANH is connected to DE-9 pin 7.You could then

plug this into an ODB-II cable to connect to a car's CAN network(). Then, you can

decode messages with software.

Terminator Jumper

The terminator jumper is located on the front of the board, to the left of the solder

pads for the edge launch DE-9 connector. It is labeled TERM and is outlined in white

on the board silk.

TERM - The board has a 120 ohm terminator connected between CANH and CA

•

NL. You can disable (remove) the terminator bycuttingtheTERMjumper, if your

bus is already terminated.

Reset Pin and Jumper

Reset Jumper - located on the back of the board, to the right of the board name

•

description, is the reset jumper. It is labeled RST and is outlined in white on the

board silk. You can cut this jumper to disconnect the MCP2515 reset pin from

the Feather reset pin.

Reset Pin - located on the front of the board in the center. It is labeled RST on

•

the silk. If you cut the reset jumper, you can use this pin to connect the MCP251

5 reset pin to a different IO pin.

Chip Select Pin and Jumper

CS Jumper - located on the back of the board, below Feather pin 5, is the chip

•

select jumper. It is labeled CS and is outlined in white on the board silk. By

default, the MCP2515 chip select pin is connected to pin 5 on the Feather. You

can cut this jumper to disconnect the MCP2515 CS pin from Feather pin 5.

CS pin - located on the front of the board in the center. It is labeled CS on the

•

silk. If you cut the CS jumper, you can use this pin to connect the MCP2515 CS

pin to a different IO pin.

©Adafruit Industries Page 7 of 13

Interrupt Pin and Jumper

INT Jumper - located on the back of the board, below Feather pin 6, is the

•

interrupt jumper. It is labeled INT and is outlined in white on the board silk. By

default, the MCP2515 interrupt pin is connected to pin 6 on the Feather. You can

cut this jumper to disconnect the MCP2515 INT pin from Feather pin 6.

INT pin - located on the front of the board in the center. It is labeled INT on the

•

silk. If you cut the INT jumper, you can use this pin to connect the MCP2515 INT

pin to a different IO pin.

Silent Mode Pin

SLNT pin - located on the front of the board in the center. It is labeled SLNT on

•

the silk. This pin can be pulled high to put the TJA1051/3 transceiver into silent

mode. From the datasheet:

In Silent mode, the transmitter is disabled, releasing the bus pins to

recessive state. All other IC functions, including the receiver, continue to

operate as in Normal mode. Silent mode can be used to prevent a faulty

CAN controller from disrupting all network communications.

CircuitPython

It's easy to use the CAN Bus FeatherWing with CircuitPython and the Adafruit_Circuit

Python_MCP2515() module. This module allows you to easily write Python code that

lets you utilize the MCP2515 CAN bus controller.

CircuitPython Microcontroller Wiring

A Feather RP2040 can connect to the CAN Bus FeatherWings by plugging them both

into a FeatherWing Doubler():

©Adafruit Industries Page 8 of 13

Plug the Feather RP2040 into one slot on

the doubler and then plug the CAN Bus

FeatherWing into the remaining slot. This

will connect all of the FeatherWing pins to

the Feather RP2040.

FeatherWing Doubler - Prototyping Add-

on For All Feather Boards

This is the FeatherWing Doubler - a

prototyping add-on and more for all

Feather boards. This is similar to our

https://www.adafruit.com/product/2890

CircuitPython Usage

To use with CircuitPython, you need to first install the MCP2515 library, and its

dependencies, into the lib folder onto your CIRCUITPY drive. Then you need to

update code.py with the example script.

Thankfully, we can do this in one go. In the example below, click the Download

Project Bundle button below to download the necessary libraries and the code.py file

in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the c

ode.py file to your CIRCUITPY drive.

Your CIRCUITPY/lib folder should contain the following folders:

adafruit_bus_device/

•

adafruit_mcp2515/

•

©Adafruit Industries Page 9 of 13

Simple Test Example

Once everything is saved to the CIRCUITPY drive, connect to the serial console() to

see the data printed out!

# SPDX-FileCopyrightText: Copyright (c) 2020 Bryan Siepert for Adafruit Industries
#
# SPDX-License-Identifier: MIT
from time import sleep
import board
import busio
from digitalio import DigitalInOut
from adafruit_mcp2515.canio import Message, RemoteTransmissionRequest
from adafruit_mcp2515 import MCP2515 as CAN

cs = DigitalInOut(board.D5)
cs.switch_to_output()
spi = busio.SPI(board.SCK, board.MOSI, board.MISO)

can_bus = CAN(
spi, cs, loopback=True, silent=True
) # use loopback to test without another device
while True:
with can_bus.listen(timeout=1.0) as listener:

message = Message(id=0x1234ABCD, data=b"adafruit", extended=True)
send_success = can_bus.send(message)
print("Send success:", send_success)
message_count = listener.in_waiting()
print(message_count, "messages available")
for _i in range(message_count):
msg = listener.receive()
print("Message from ", hex(msg.id))
if isinstance(msg, Message):
print("message data:", msg.data)
if isinstance(msg, RemoteTransmissionRequest):
print("RTR length:", msg.length)
sleep(1)

In the code, the instantiation of can_bus sets loopback and silent to True . This

allows you to test the CAN Bus messaging without another CAN device.

can_bus = CAN(
spi, cs, loopback=True, silent=True
) # use loopback to test without another device

©Adafruit Industries Page 10 of 13

In the REPL, you'll see the byte array message be sent successfully every second.

Testing with Two CAN Bus FeatherWings

You can test with two CAN Bus FeatherWings by preparing two FeatherWing Doublers

with Feather RP2040s and CAN Bus FeatherWings.

Once you have two Feather RP2040's

connected to CAN Bus FeatherWings, you

can connect the CAN signals:

FeatherWing A CANH terminal block to

FeatherWing B CANH terminal block (blue

wire)

FeatherWing A - (ground) terminal block to

FeatherWing B - (ground) terminal block

(black wire)

FeatherWing A CANL terminal block to

FeatherWing B CANL terminal block

(yellow wire)

Upload the Project Bundle to both CIRCUITPY drives. In the code, change the can_bu

s instantiation on both Feather RP2040's to have loopback and silent be

False .

can_bus = CAN(
spi, cs, loopback=False, silent=False
) # use loopback to test without another device

When you run the code on both Feather boards, you can check each REPL window

and see messages being exchanged between the two boards.

©Adafruit Industries Page 11 of 13

Python Docs

Python Docs()

Downloads

Files

MCP2515 Datasheet()

•

TJA1051/3 Datasheet()

•

EagleCAD PCB files on GitHub()

•

Fritzing object in the Adafruit Fritzing Library()

•

Schematic and Fab Print

©Adafruit Industries Page 12 of 13

Dimensions are in inches.

©Adafruit Industries Page 13 of 13