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Thread: Ethernet Watchdog board based on Teensy 3.2

  1. #1
    Junior Member
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    Dec 2016
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    Ethernet Watchdog board based on Teensy 3.2

    I recently had the need to attach an Ethernet-based watchdog board to a couple of computers controlling a (research) nuclear reactor. Search though I did for a COTS product, I was unable to find something that was:

    1) Failsafe operation (you would think watchdog timers would get this right, a surprising number of them don't)
    2) Easy to use without a massive amount of configuration or programming
    3) Relatively inexpensive (under $500, in my case).
    4) Capable of handling watchdog facilities for two PCs (though, if cheap enough, I could just purchase two of them)
    5) Provides at least three relays for each watchdog channel (two channels was desired; once again, I could have just purchased two board for multiple channels)
    6) Includes a *hardware* watchdog timer to verify that the firmware-based code is operating properly

    As you can imagine, the DOE and NRC are a bit anal retentive about things being hooked up to a nuclear reactor. So another requirement was

    7) Open source along with full schematics

    to allow reviewing the design for any security issues.

    As you can possibly imagine, finding a device with these requirements was difficult (impossible, for me).

    So I built my own using a Teensy 3.2 and a small number of components.
    The full description of this project (along with firmware, gerber files for the PCB, etc.) can be found here:

    http://www.plantation-productions.co...s/EWB/EWB.html

    Features of the Ethernet Watchdog Board (EWB) include:

    1) Failsafe design. If power is removed, the watchdog relays are in the open position (assuming use of NO contacts).
    2) Hardware-based watchdog circuit monitors the Teensy 3.2 firmware; if it stops updating the TA8030S watchdog timer IC, this triggers a watchdog timeout event on the EWB which causes *all* the relays to open.
    3) 8-channel relay board supports 1-8 channels; the default firmware provides two channels, each channel controls four relays in tandem (in my particular case, I need three relays for each channel - one for the reactor SCRAM circuitry, one to supply a digital input to the PCs, and one to control an indicator lamp on the console).
    4) Adafruit Feather bus included (I use an Adafruit Ethernet Featherwing for the Ethernet interface)
    5) SPI bus connections for SPI-based Ethernet adapters (non-feather based).
    6) 1x10 header that connects to a COTS 8-channel relay board (under $10 on Amazon, very common design available from multiple manufacturers). A second header reverses the pins to make connections easier, depending on how one mounts the EWB and relay boards.
    7) 5 LEDs for Power, heartbeat, Ch1 live, Ch2 live, and HW WD trip.

    I've also provided a set of 3D printer files (STL) for printing a stand for the relay board and EWB.

    FWIW, the EWB also makes a half-way decent breakout board for the Teensy 3.2. It brings out all pins except A14 to various headers on the EWB.

    All open source/open hardware.
    Enjoy.

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    9,967
    Nice work and great looking assembly and detail writeup.

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