70a5e48ab8
- Start: 1 CAN, 1 12V (bus origin) - Minor: 3 CAN, 1 12V (intermediate) - Middle: 3 CAN, 2 12V (intermediate + power) - Major: 6 CAN, 2 12V (end of chain) - Endz: 1 CAN, 1 12V + USB diagnostic (start or end) - All have shunt-activated 120Ω termination
4.8 KiB
title, tags, type, owner, status, sources
| title | tags | type | owner | status | sources | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Canjectors — Chris's Custom CAN Bus Interconnect System |
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hardware-spec | 2890 | active |
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Canjectors — Custom CAN Bus Interconnect System
Overview
After experiencing critical CAN bus failures during competition, Chris designed the Canjector system as a robust interconnect solution for Team 2890's robot. Modeled after the SWYFT CANnect concept but with custom design work, Canjectors provide reliable CAN + power distribution at all critical connections.
The design philosophy: prevent wiring failures from killing the robot mid-match.
Design Basis
Chris studied the SWYFT CANnect system as inspiration:
- Run CAN bus + 12V power over standardized cabling
- Easy connector system (WAGO lever terminals)
- Built-in CAN termination options
- Robust form factor
Canjectors go further with custom modifications for Team 2890's specific failure points.
Current Design: Middle Canjector
The schematic shows the "middle" Canjector variant with:
- 12V power passthrough
- 3 CAN connections (RJ45 connectors)
- WAGO terminal blocks for clean wiring (2601-1104 series)
- 120Ω termination resistor (R4) between CAN signal lines — switchable
- Power indicator LED (green, 0603) with 470Ω current limiting resistor
- 2-pin header for additional configuration
Key Features
- Dual CAN paths — each Canjector bridges multiple CAN segments
- Integrated termination — 120Ω resistor switchable per segment
- Power LED — visual confirmation that 12V is present
- RJ45 connectors — industry standard, easy to cable, robust
- WAGO 2601 series — tool-free, reliable terminal connections
- Designed in EasyEDA — schematic dated 2026-04-09
Design Variants
Chris designed five Canjector variants to form a complete CAN bus distribution system. All variants support configurable termination via a shunt jumper — populate the shunt to activate 120Ω termination at any position in the chain.
| Variant | CAN connections | 12V outputs | Termination | Typical use |
|---|---|---|---|---|
| Start | 1 | 1 | Shunt-activated | Bus origin at PDH |
| Minor | 3 | 1 | Shunt-activated | Intermediate node |
| Middle | 3 | 2 | Shunt-activated | Intermediate node + power distribution |
| Major | 6 | 2 | Shunt-activated | End of chain (large node) |
| Endz | 1 | 1 | Shunt-activated | Start OR final terminator — diagnostic USB interface |
All Canjectors share the same termination philosophy: no fixed termination at any position. Use a shunt jumper to enable 120Ω termination exactly where the bus physics require it. This eliminates the need for separate "terminating" and "non-terminating" variants.
Endz is unique — it's the diagnostic variant with a USB Type-B connector for direct laptop-to-CAN connection. Meant to serve as either the first or last device in the chain. Currently experiencing design problems; no working units on hand.
Connection to Training
For students: CAN bus failures are among the most frustrating problems in FRC — a loose wire or failed connector kills the whole bus. The Canjector system teaches:
- Redundancy — when one path fails, traffic routes around it
- Termination — 120Ω at each end of the bus, switchable at intermediate nodes
- Visual debugging — power LEDs let you confirm connectivity at a glance
- Modular design — if one Canjector fails, replace it in minutes
Why This Matters
Chris experienced critical CAN failures at competition. The Canjector system is a direct response — solving the failure mode with custom hardware instead of hoping the stock connectors hold. This is the kind of real-world engineering that separates good teams from great ones.
Notes for MrC
This is a confidence builder for the training vault — it shows Chris's practical engineering under pressure. Good story for students: identify the problem, study existing solutions, design your own, build it, test it. The full engineering cycle, not just code.
Files
| File | Description |
|---|---|
canjector-schematic.png |
Middle Canjector — EasyEDA schematic |
canjector-start-pcb.png |
Start variant — PCB layout (red solder mask) |
canjector-minor-render.png |
Minor variant — 3D render, blue PCB |
canjector-major-render.png |
Major variant — 3D render, blue PCB, 6 CAN ports |
canjector-endz-render.png |
Endz variant — USB-to-CAN diagnostic interface |
canjectors.md |
This documentation file |
canjector-gerbers/ |
Major variant manufacturing files |
canjector-minor-gerbers/ |
Minor variant manufacturing files |
canjector-endz-gerbers/ |
Endz variant manufacturing files |