CAN Hacking: The Hardware


So far we have discussed the basics of CAN, in-vehicle networks, and protocols used over CAN. We’re going to wrap up with a discussion of CAN tools, and parts to build your own CAN hardware.


Unfortunately, there’s no set standard for CAN connections. The most common connector for high-speed CAN is a DE-9, with CAN high on pin 7 and CAN low on pin 2. However cables will differ, and many are incompatible.

CAN needs to be terminated, preferably by a 120 ohm resistance on either end of the bus. In practice, you can stick a single 120 ohm resistor across the bus to deal with termination.


A good CAN tool will let you transmit and receive CAN messages, interpret live data using CAN databases, and talk CAN protocols. The tools with this feature set are proprietary and expensive, but some hacker friendly options exist.


The GoodThopter12

Based on [Travis Goodspeed's] GoodFET, the GoodThopter by [Q] uses the Microchip MCP2515 CAN to SPI controller to access the bus. The open hardware tool lets you send and receive messages using Python scripts.

CAN Bus Triple

CAN Bus Triple

The CAN Bus Triple device provides an interface to three CAN buses, and can be programmed in an environment similar to Arduino. The open source code provided lets you muck with the second generation Mazda 3. Unfortunately, the hardware does not appear to be open source.

Saleae Logic

Saleae Logic

It’s not open source, but the Saleae Logic is a very handy and cheap tool for looking at CAN buses. It can capture, decode, and display CAN traffic. This is most useful when you’re building your own CAN hardware.


The Parts

If you want to design your own hardware for CAN, you’ll need two things: a CAN controller, and a CAN transceiver.

The CAN controller generates and interprets CAN messages. There’s many microcontrollers on the market with built-in CAN controllers, such as the Atmel ATmega32M1, Freescale S08D, and the TI Tiva C Series. When using a built-in CAN controller, you’ll have to use an external oscillator, internal oscillators are not sufficiently accurate for high-speed CAN. If you want to add CAN to an existing microcontroller, the MCP2515 is an option. It’s a standalone CAN controller that communicates over SPI.

The transceiver translates signals from the controller to the bus, and from the bus to the transceiver. Different transceivers are needed for high-speed and low-speed CAN networks. The NXP TJA1050 works with high-speed buses, and the ON Semi NCV7356 works with low-speed, single wire buses.

Dev Boards

There’s a ton of development boards out there featuring microcontrollers with a CAN controller. The Arduino Due‘s SAM3 processor has a controller, but there’s no transceiver on the board. You can pick up a CAN bus shield, and the Due CAN Library to get started.

The ChipKIT Max32 is similar to the Due. It has two CAN controllers, but you’ll need to provide external transceivers to actually get on a bus. Fortunately there’s a shield for that. The ChipKIT is officially supported by Ford’s OpenXC Platform, so you can grab their firmware.

That concludes our discussion of CAN Hacking. Hopefully you’re now ready to go out and experiment with the protocol. If you have questions, send them along to our tip line with “CAN Hacking” in the subject, and we’ll compile some answers. If you liked this series and want to suggest a topic for the next set of posts we’d love to hear that as well!

CAN Hacking

CAN Hacking: Protocols


We’ve gone over the basics of CAN and looked into how CAN databases work. Now we will look at a few protocols that are commonly used over CAN.

In the last article we looked at CAN databases, where each bit of a message is mapped to a specific meaning. For example, bit 1 of a CAN message with ID 0×400 might represent whether the engine is currently running or not.

However, for more complex communications we need to use protocols. These can map many meanings to a single CAN ID by agreeing on a structure for sending and receiving data.

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CAN Hacking: The In-vehicle Network

Last time, we discussed how in-vehicle networks work over CAN. Now we’ll look into the protocol and how it’s used in the automotive industry.

The Bus

On the hardware side, there’s two types of CAN: differential (or high-speed) and single wire. Differential uses two wires and can operate up to 1 Mbps. Single wire runs on a single wire, and at lower speeds, but is cheaper to implement. Differential is used in more critical applications, such as engine control, and single wire is used for less important things, such as HVAC and window control.

Many controllers can connect to the same bus in a multi-master configuration. All messages are broadcast to every controller on the bus.

An oversimplified in-vehicle network

An oversimplified in-vehicle network

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CAN Hacking: Introductions

CAN Frame

We’re introducing a new series on CAN and automotive hacking. First, we’ll introduce CAN and discuss how in-vehicle networks work.

In 1986, Bosch introduced the Controller Area Network protocol. It was designed specifically for in-vehicle networks between automotive controllers. CAN became a popular option for networking controllers in automotive, industrial, and robotics applications. Starting in 2008, all vehicles sold in the US must use CAN.

Modern vehicles are distributed control systems, with controllers designed to handle specific tasks. For example, a door control module would take care of locks and windows. CAN allows these controllers to communicate. It also allows for external systems to perform diagnostic tasks by connecting to the in-vehicle network.

Some examples of CAN communication in a vehicle include:

  • The engine control module sending the current engine speed to the instrument cluster, where it is displayed on a tachometer.
  • The driver’s door controller sending a message to another door controller to actuate the window.
  • A firmware upgrade for a controller, sent from a diagnostics tool.

CAN is usually used with little or no security, except for the obscurity of the communications. We can use CAN to USB interfaces to listen to the traffic, and then decode it. We can also use these tools to send forged messages, or to perform diagnostic actions. Unfortunately, most of the tools for dealing with CAN are proprietary, and very expensive. The diagnostics protocols are standards, but not open ones. They must be purchased from the International Organization for Standardization.

Next time, we’ll get into the structure of CAN frames, and how traffic is encoded on the bus.

 [Image via Wikipedia]

CAN Hacking

DEF CON: Hacking Hardware and Cars

DEF CON Hardware Hacking Village

The first full day of DEF CON was packed with hacking hardware and cars. I got to learn about why your car is less secure than you might think, pick some locks, and found out that there are electronic DEF CON badges after all. Keep reading for all the detail.

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Relighting a gauge cluster

When a few lights in the dashboard of  [Garrett]‘s truck burned out, he was looking at a hefty repair bill. The repair shop would have to replace the huge PCB to change a few soldered light bulbs, so he was looking at a $500 repair bill. Lighting up a LED is everyone’s first project, so [Garrett] decided to change out the bulbs with LEDs and save a few dollars.

The repair was very simple – after removing the dials and needles, [Garrett] found a huge PCB with a few burnt out bulbs on board. He took a multimeter to each bulb’s solder pad and replaced each one with an LED and resistor. The finished project looks like it came out of a factory and is a huge improvement over the ugly amber bulbs originally found in his truck.  [Garrett] also posted a nice Instructable of his build showing the nicely soldered lamp replacements.

DIY wiper speed control and collision avoidance


On many new cars, automatic wiper speed control can be had as an upgrade, though most cars do not offer front-end collision prevention at all. [Rishi Hora] and [Diwakar Labh], students at the Guru Tegh Bahadur Institute of Technology in New Delhi, developed their own version of these features, (PDF warning, skip to page 20) which they entered into last year’s Texas Instruments Analog Design Contest. Under the guidance of professors [Gurmeet Singh] and [Pawan Kumar], the pair built the systems using easily obtainable parts, including of course, an MSP430 microcontroller from TI.

The collision prevention system uses a laser emitter and an optical detector to estimate the distance between your car and the vehicle in front of you, sounding an alarm if you are getting too close. In a somewhat similar fashion, the wiper speed control system uses an IR emitter and detector pair to estimate the amount of water built up on the windshield, triggering the wipers when necessary.

While not groundbreaking, the systems would be quite handy during monsoon season in India, and seem easy enough to install in an older vehicle. The only thing we’re not so sure about is pointing lasers at cars in traffic, but there are quite a few available alternatives that can be used to measure distance.

Continue reading to see a video walkthrough and demonstration of both systems.

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