Fathom-S Tether Interface Board Set


The Fathom-S boards provide low-latency video, a serial port connection, and remote power on/off switch for tethers of 300+m length. Use with the Fathom tether or a Cat5+ network cable.

In stock

HS Code: 8504.40.40

Product Description

The Fathom-S Tether Interface Board Set provides the communication and video signals needed for an ROV. It interfaces with the Fathom tether or any standard Cat5 cable with four twisted pairs of wire. It has the following features:

Through the Tether

  • Low-latency analog video using a differential video amplifier for crisp, colorful video over 300+m of cable. It’s compatible with any camera that has a standard NTSC or PAL video output.
  • Long-distance serial connection using RS-422 differential amplifiers for high-speed, reliable communication over 600+m of cable
  • Power on/off switch allows you to switch power on and off for small electronics electronics. For high power switching, this can interface to a high-current power switching board.

Topside Interface

  • Screw terminals for tether connection
  • RCA video output compatible with any NTSC/PAL display or video capture card
  • USB serial port to easily connect to a computer
  • TTL serial port (5V) for direct interfacing to a computer or microcontroller
  • Power-on is switched on when connected through USB or powered otherwise
  • Jumper for reset-on-RTS to allow Arduino microcontrollers to be programmed through the tether
  • Optional external power input (7-20V)

ROV-side Interface

  • Screw terminals for tether connection
  • Header pin connection for analog camera
  • 12V regulator for analog camera, accepting up to 20V input
  • TTL serial port (3.3V logic, 5V tolerant) compatible with Arduino, Raspberry Pi, and DroneCode autopilots
  • DroneCode Mini compatible connectors for quick connection to Pixhawk and other DroneCode autopilots
  • 5V regulator to power low-current electronics such as an Arduino
  • Jumper to enable/disable tether power switch

The Fathom-S Tether Interface Board Set is open-source and open-hardware, so the schematics and board files are free to view, modify, and reuse. The electrical schematic and board layout are open-source and the design files are available.


  • 1 x Topside Interface Board
  • 1 x ROV Interface Board
  • 2 x 2mm jumper


Supply Voltage7 - 20 volts
TTL Serial Voltage (ROV Board)3.3 volts (5v tolerant)
TTL Serial Voltage (Topside Board)5 volts
Camera Supply Voltage (if Vin > 12v)12 volts
Max 5V Load Current (@ 12 Vin)250 mA
Max 5V Load Current (@ 16 Vin)150 mA
Max 12V Load Current (@ 12 Vin)600 mA
Max 12V Load Current (@ 16 Vin)250 mA
Switched Power Voltage (SW Header)Vbat
Switched Power Current (SW Header)2A
Max Serial Baudrate250 Kbps
Max Tether Length (RS422)1200 m
Max Tether Length (Video)300 m
Operating Temperature-20 to +85°C
Storage Temperature-40 to +85°C
DF13 UART PinoutDroneCode Mini Standard (crossover RX/TX)
JST-GH UART PinoutDroneCode Mini Standard (crossover RX/TX)
USB Connector TypeUSB Mini B Female
Screw Hole Diameter3.3 mm

2D Drawings

ROV Board

Fathom-S ROV Diagram

Topside Board

Fathom-S Topside Diagram

3D Models




Fathom-S Schematic (PDF)

Fathom-S Design Files (Github)

Revision History

18 May 2016

  • R1 – Initial release

Quick Start

1. Connect tether cable to the terminal block, matching colors with the labels

2. Connect the ROV side serial port to the ROV controller (Arduino, Pixhawk, etc.)

3. Connect an analog camera to the ROV side camera input

4. Connect the topside board to an analog (NTSC/PAL) display and a computer USB port to view video and communicate through serial


Fathom-S Usage Guide

Learn how to connect a Fathom-S board to a Pixhawk or Arduino board!


Blue Robotics Forum – Tether Interfaces