COSMIIC Remote Module Network Interface

The Remote Module Network Interface is the shared circuit block present on every COSMIIC remote module (PG4, BP2, and derivatives). It bridges the AT90CAN128's built-in CAN controller to the implanted 2-conductor network, extracts regulated 5V from the network supply, and fans out to 4 ports (1 upstream in + 3 downstream out) for branching tree topology.

How it works

Every remote module connects to the COSMIIC implanted network through a single 2-conductor cable. That cable carries both the CANopen differential bus and the DC supply voltage on the same conductors (NET_P = CANH / supply+, NET_N = CANL / supply return). The network interface circuit:

1. Extracts regulated 5V — NET_P (4.7–9.6 V from the PM) feeds the U2 LDO; regulated 5V powers the AT90CAN128 and the CAN transceiver
2. Transceives CAN — U1 (TJA1050T) bridges the AT90CAN128's digital CANTX/CANRX pins to the physical CANH/CANL bus
3. Fans out to 4 ports — J1–J4 connectors branch the same CAN bus to 1 upstream input + 3 downstream outputs
4. Hardware node addressing — MC_ANODE exposes the hardware node address line to the AT90CAN128

U1's Rs pin is pulled low through R1 (10 kΩ) for slope-controlled mode, which limits dV/dt on the bus edges and reduces EMI — important for implantable devices.

Hardware

Components

Production note: For the full 4.7–9.6 V network range, replace U2 with LM1117S-5.0 (C126028, SOT-223-3, 800 mA) which handles up to 15 V input.

Signal Net Names

Machine Contacts

Architecture

        Network Cable (2-wire: NET_P/CANH and NET_N/CANL)
                │
    ┌───────────▼─────────────┐
    │   J1 — Port 1 (in)      │
    └───────────┬─────────────┘
                │
    ┌───────────▼──────────────────────────────────┐
    │        Network Interface (32×24mm)           │
    │                                              │
    │  ┌──────────────┐   ┌────────────────────┐  │
    │  │ U2 MIC5205   │   │ U1 TJA1050T        │  │
    │  │ 5V LDO       │   │ CAN Transceiver    │  │
    │  │ NET_P → 5V   │   │ CANTX/CANRX (MCU)  │  │
    │  └──────┬───────┘   │ CANH/CANL (bus)    │  │
    │         │ VCC       └──────┬──────────────┘  │
    │         └──────────────────┤                 │
    │                            │ CANH / CANL     │
    └────────────────────────────┼─────────────────┘
                │          │          │
    ┌───────────▼─┐ ┌───────▼──┐ ┌───▼────────┐
    │ J2 (out 1)  │ │J3 (out 2)│ │J4 (out 3)  │
    └─────────────┘ └──────────┘ └────────────┘

CANopen Protocol

The PM acts as NMT master; remote modules are NMT slaves.

Build

EDA: tscircuit (TSX) — source bundle included in Files below.

LDO note: Production modules use LM1117S-5.0 (C126028, SOT-223) which handles the full 4.7–9.6V network range. The SOT-23-5 MIC5205 in this reference design targets bench testing where network voltage is kept ≤6V.

Firmware: COSMIIC-Community/Implantables-PG4-App / Implantables-BP2-App — C, AVR toolchain

Source

All design files are open source under CERN-OHL-P-2.0 (hardware) and MIT (firmware).

Files

Reference Implementation

The equivalent analog circuit appears as a dedicated schematic sheet in every remote module Altium project:

• PG4 — page 4 of 8 ("CAN Interface") in COSMIIC-Community/Implantables-PG4-Hardware
• BP2 — page 4 of 6 ("Network Interface") in COSMIIC-Community/Implantables-BP2-Hardware

NSF Relevance

The standardized remote module network interface enables multi-node implantable research systems with a single power and communication cable per branch. Researchers can add sensing or stimulation nodes to a running implant without architectural changes, enabling adaptive closed-loop protocols with real-time bidirectional data flow.

Science Drivers

implantable_healthcare

Created by: noah
Version: v1
Category: other