Machine Access Node

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Hackspace has machines, that ideally need to be inducted and access controls for safety reasons. A vital step towards the goal of 24/7 access on membership. A bonus of the system would be usage tracking and maintenance notifications.

A solution is a control device consisting of a box which enables the machine for as long as your RFID card is in the box. A Tool Access Node.

Potential design

  • ESP-12F module
  • 3A Relay
  • bicolour LED (red/green)
  • Card interface header (6 pin SPI bus presenting power & ground)
  • DIP switch addressable (or other)

Functional Specs

Mission Critical

These must work without networking or the main server being avalable.

  • Check if card valid in local storage
  • Set tool into "out of order" mode - must work without networking


  • Relay contacts of at least 3 amps for switching the device (this would be best driving a contactor coil rather than the machine itself, as carrying machine current on a board seems bad). Hard-wired in using suitable grommets and with sufficient isolation between low and high voltage.
  • Internal database of (up to at least 200*) authorised RFID card IDs, plus a flexible way of fetching updates from a membership server.
  • Logging of who used the machine + hours used.
  • Open Source hardware & software.
  • Status light, for "active", "denied" and "thinking". (Although "active" is really the only important one, and blinking is fine). To build upon this, various different colours could indicate different things such as blinking green means valid, but offline and solid green means valid & online
  • Fits in a standard backbox (probably deep depth, ideally single unit)


  • Ideally sub-£30.
  • Mains Powered
  • Ability for super-users to program new cards from the device - this should result in a callback to a membership server to verify it.
  • Easy to program/modify
  • Ability to monitor "actual" hours run - i.e. how long the laser cutter tube is actually on for. (This could potentially be done using a current transformer sensor.)
  • Ability to poll for current state over the network.
  • Broadcast events on the network.
  • Ability to update the software over the network.
  • Relay / Darlington / Servo output configurations.