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Table of Contents
Tool Access Controllers
Overview
We have access control for some of our power tools, especially where they are dangerous, expensive or easily damaged by untrained users.
The access controllers are built on the ESP8266 platform and use PN532 modules to authenticate NFC tokens.
Each controller can manage a single tool and enable/disable it's incoming power, or integrate into a more complex control system. The controllers can also perform a basic current usage measurement to determine whether a tool is in active use.
PCB
https://github.com/timhawes/stony_skunk/
Revision 1 had an error in the layout and was not used.
Revision 2 uses an ESP-12E module and has been deployed on many of the lab's tools.
Revision 3 uses a Wemos D1 Mini module for easier builds and debugging.
| Ref | Item | Quantity | Selection |
|---|---|---|---|
| U1 | Wemos D1 Mini | 1 | |
| U2 | TE OJ/OJE series 5V relay | 1 | Farnell 1891661 |
| SP1 | 12.7mm through-hole buzzer | 1 | CPC LS03778 or LS00654 |
| D1 | Flyback diode | 1 | Farnell 1625280 (US1D) |
| D2 | ESD protection diode | 1 | Farnell 2317508 (ESD5Z3.3T1G) |
| Q1, Q2 | N-channel MOSFET SOT-23 | 2 | Farnell 2069541 |
| C3 | 10uF capacitor | 1 | |
| R1, R6, R7, R13 | 10K 0603 | 3 | |
| R3, R4 | n/a | burden resistor, easier to fit one externally | |
| R5 | 1K 0603 | 1 | |
| R8, R9 | 2K2 0603 | 2 | |
| P1 | 8-way 3.5mm screw terminal | 1 | |
| P2 | 4-way 0.1“ pin header | 1 | |
| P3 | 2-way 5mm pluggable screw terminal | 1 | CPC CN18918 + CPC CN18994 |
| P4 | 5-way 0.1” pin header | 1 | |
| P7 | 2-way 0.1“ pin header | 1 |
Other Components
To make a working system, the following components will be required in addition to the PCB:
| 20×4 LCD module with I2C backpack | by convention we use black text on a yellow backlight, which is more readable than white on blue |
| PN532 NFC module | Buy direct from Elechouse, clones have poor read range and a high failure rate |
| Two push buttons | CPC SW03314 |
| Current transformer | DL-CT08CL5-20A plus 33R burden resistor |
Depending on the tool being managed:
| 5V 1A power supply | 240V AC-DC, 24V DC-DC from a VFD or 5V from an existing PSU |
| AC contactor or no-volt switch |
Enclosure and Wiring
All of our current tool controllers use the same design, an IP65 ABS enclosure from RadioWorld on eBay.
The PCB, LCD and NFC modules are mounted on a laser-cut acrylic frame using nylon screws and spacers. Push buttons are panel-mounted to the front of the enclosure.
Simple plug-in mains tools:
On a simple tools up to 10A, we use two cable glands for the incoming mains and outgoing switched-mains. The onboard 10A relay is used for switching and the current transformer is fitted inside the enclosure. It is assumed that the relay will not normally switch the full load so we don't de-rate for inductive loads.
More powerful tools:
On more powerful tools we fit a no-volt switch or contactor. Our 10A relay is put in series with the contactor coil supply so that the contactor can be locked-out. The current transformer will be located remotely to measure the full system load or just the motors.
Other:
More complex tools may have their own control systems (remote start/stop, VFD motor controllers, etc). In these cases we may fit our relay to the incoming contactor or to the control signals loop or to the estop/interlock loop.
Software
Two generations of firmware and backend-server are in use at the moment:
Legacy/Stable:
- uses UDP networking with a simple retry mechanism for reliability
New:
- uses TCP networking with optional TLS support
Bugs and Improvements
- Delay active→idle transition to avoid triggering on current-measurement glitches.
- In wait mode, delay idle logout by 1-2 seconds.
- Flatten floods of NFC reads.