Chimera

Introduction

Chimera is the bridge between your car's brain and the RetroPilot system. It's designed to read critical vehicle information and translate it into a language that RetroPilot Cores and your chosen compute can understand. Whether your car has a modern CAN bus or older, direct sensor signals, Chimera is flexible enough to get the data it needs. This guide will walk you through the basics of the Chimera, showing you how to connect everything and configure it using the included utility.

Features

Power & IO

• Flexible Power Outputs: The board provides both 3.3V and 5V outputs to power your connected hardware.

• Secure Power Connections: Use the dedicated 4mm screw terminals to safely connect your car's 12V battery and ground. All inputs and outputs are fused for protection.

• Intelligent Power Control: Chimera includes an on-board relay to control power for up to three connected devices on CAN0, such as RetroPilot Cores.

CAN Connectivity

• CAN0: Six connections are dedicated to the primary CAN0 bus. This is where you'll connect your RetroPilot Cores or any device you need to control, such as StepperServoCAN.

  • Power: On the CAN0 header, three power outputs are labeled 12VR, meaning they are switched on and off by the on-board relay. The other three are labeled IGN, and they are active whenever your car's ignition is on.

• CAN1 (ADAS): Three connections are available for CAN1. Use this bus to connect radars or other ADAS-specific sensors.

  • Power: All power outputs on the CAN1 header are labeled IGN, so they are active whenever your car's ignition is on.

• CAN2 (Vehicle & Retrofit): Three connections are for CAN2. This is a versatile bus you can use to tap into your car's existing CAN network. If your car isn't CAN-equipped, you can use this bus to connect and integrate sensors you're retrofitting, such as steering angle sensors or ABS units.

  • Power: All power outputs on the CAN2 header are also labeled IGN, meaning they are active whenever the ignition is on. If your car isn't CAN-equipped, you can use this bus to connect and integrate sensors you're retrofitting, such as steering angle sensors or ABS units.

Tools & Compatibility

• USB Port: An on-board USB port allows you to connect a computer for easy configuration and real-time CAN bus analysis.

• Panda APIs: The Chimera is fully compatible with the Comma.ai Panda APIs for sending and receiving CAN messages.

• OBD-C Port: A dedicated port makes it simple to connect other Comma devices.

• Open Source: The firmware for Chimera is completely Free and Open-Source Software (FOSS) and available on GitHub, giving you full transparency and control.

Hardware Overview

Before you begin installation, it's important to familiarize yourself with the key components on the Chimera board. Below is a breakdown of the main connection points and features.

Power & I/O

• 12V Power Terminals: The two large screw terminal blocks are your main power inputs. This is where you will connect the Chimera directly to your car's battery. Here, the one near +BATT is the 12V VBATT terminal and the one labeled T2 is ground. Use an M4 eyelet ring terminal, crimped onto 10AWG wire, to make the connection. This input is fused, and a 30A mini fuse is recommended.

• Fused Outputs (OUT1, OUT2, OUT3): These screw terminal blocks are your main power outputs. They are designed to connect to high-current devices like an Actuator Core or a Relay Core. Each of these outputs has its own dedicated fuse for protection. Fuse these in accordance with what's being plugged in. For example, Actuator Core needs a 15A fuse while Relay Core only needs a 5A fuse.

• Auxiliary Power & Ground: A smaller screw terminal block provides outputs for 5V, 3.3V, and GND to power smaller, low-current components.

• Analog and Sensor Inputs:

  • IGN is used to connect to the cars ignition line, which powers chimera when not connected by USB and also powers connected devices not controlled by the relay.

  • VSS connects to a digital Vehicle Speed Sensor¹

  • CPS connects to the car's Crankshaft Position Sensor¹

  • BRAKE connects to the Brake Light Switch

  • ADC1 and ADC2 are used to connect to your car's Cruise Control Stalk if it's a resistive type

CAN Connectivity

• CAN0, CAN1, and CAN2 Terminals: These screw terminal blocks are where you will connect to your vehicle's CAN buses. As detailed in the features section, these terminals also provide power outputs, some of which are controlled by the on-board relay.

• CAN Termination Headers: The board includes a header for each CAN bus. If you need to terminate a bus, simply install a jumper on the corresponding header.

Ports & Buttons

• USB Port: The USB Type B port is your main connection for configuring the Chimera and for real-time CAN bus analysis.

• OBD-C Port: A standard OBD-C port is provided for quick and easy connection to other Comma devices.

• DFU & Reset Buttons: These buttons are used for entering Device Firmware Update mode and for resetting the board, respectively.

Pinout

CAN0 (ports 1, 2, and 3)

CAN0 (ports 4, 5, and 6), CAN1 & CAN2

Aux Power header

Sensor Inputs

Power Outputs (OUT1, OUT2, OUT3)

On these, the label just says +OUT1, +OUT2, and +OUT3. The + denotes which terminal is +12V, while the other is GND.

Installation

Installation procedures will vary according to what is available on the car. For instance, a 2014 Honda CRV has a native CAN bus and so will not require the sensor inputs to be connected at all since all the data can be obtained from the CAN bus. In that case, all that needs to be connected to Chimera is the following:

Cars after 2008 (generally)

• +BATT to 12V from the battery, via a 10 AWG wire

• T2/GND to the car's ground, via a 10 AWG wire

• IGN to the car's ignition line

• CANH (on CAN2) to the car's CAN bus High

• CANL (on CAN2) to the car's CAN bus Low

Cars before 2008 (generally)

• +BATT to 12V from the battery, via a 10 AWG wire

• T2/GND to the car's ground, via a 10 AWG wire

• IGN to the car's ignition line

• VSS to the car's vehicle speed sensor ¹

• CPS to the car's Crank Postion Sensor^{1 2}

• BRAKE to the car's Brake Light Switch output³

• ADC1 or ADC2 to the car's Cruise Control Switch. If the switch is a simple resistor divider type, install an appropriate pull-up resistor between the ADC input and either 3.3V or 5V.

• Retrofitted Steering Angle Sensor (Required) on CAN2, following the sensor manufacturer's pinout

Software setup

Flashing and configuration are made easy by the console-based config tool. To run it, first install pipenv, then set up the environment with pipenv install in the root directory of ocelot.

Running the Script

Once the environment is set up, the config utility can be run with ./stm_config_tool.py

• The script lists all supported devices connected over USB.

• Select the Chimera device from the menu.

• The script will read the flash config and display current entries.

• You will then see the available Chimera configuration options.

Chimera Config Options

Each option is tied to a Flash Index inside Chimera’s non-volatile storage. When selected, the script prompts you to choose a type (CAN, ADC, VSS, or SYS) and enter the required fields.

Configuration Types

Depending on the option, you’ll be prompted to enter values in one of the following formats:

1. CAN

• can_id: Message ID (hex or decimal).

• scale_offs: Offset applied to raw value.

• scale_mult: Multiplier applied to raw value.

• msg_len_bytes: Message length in bytes.

• sig_type: Type of signal

• shift_amt: Bit shift inside CAN frame.

• sig_len: Bit length of the signal.

• endian_type: 0 = little endian, 1 = big endian.

• enabled: 1 = active, 0 = disabled.

• is_signed: 1 = signed value, 0 = unsigned.

2. ADC

• adc1: ADC Ch 1 value (when pressed)

• adc2: ADC Ch 2 value (when pressed)

• adc_tolerance: Allowed tolerance (deadband).

• adc_num: Which ADC channel (0 or 1).

• adc_en: Enable (1) or disable (0) this ADC input.

3. SYS

• debug_lvl: Verbosity of debug output.

• can_out_en: Enable (1) or disable (0) CAN forwarding/output.

• iwdg_en: Enable (1) or disable (0) the watchdog timer.

4. VSS

• vss_ppd: Pulses per distance unit (per km or per mile).

• is_kph: Metric flag (1 = km/h, 0 = mph).

Workflow Example (Chimera + Vehicle Speed)

Example: Configure Chimera to read Vehicle Speed from CAN.

1. Run script and select Chimera device.

2. From config list, choose Vehicle Speed (Flash Index 4).

3. Choose type CAN.

4. Enter CAN parameters (e.g. can_id=0x123, scale_mult=1, etc).

5. Confirm write — config will be saved to flash.

Notes

• Unformatted flash: If the script reports Invalid config magic, you’ll be prompted to format the device. This wipes all stored configs.

• Indexes not listed: Only the indexes above are valid for Chimera. Others are reserved.

• Multiple types: Some entries (e.g. Vehicle Speed, Cruise buttons) allow multiple types (CAN or ADC).

Troubleshooting

Configuration

Footnotes: (1) check your car's repair manual or use an oscilloscope to verify it's a square wave and not AC sine (2) optional (3) optional if retrofitting an iBooster