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Emergency power off controller

From CaveLab
This page is kept for historical interest. It may document projects or methods that are obsolete and/or no longer relevant. The information here is not kept up-to-date.

This module was part of the rack box project — which was terminated when I moved out of my first apartment.
EMG (left) with Fuse box 1 (right)

Emergency stop controller for the rack box project. Uses two 555 timers.


EMG will cut the main power to the Rack box if emergency shutdown is activated. The module is powered by the 12V power supply, this supply is referred to as emergency supply. Main fuses are located on the EMG front, a green LED shows that voltage is present. If one of the fuses should burn out Main monitoring unit will signal a supply error. The big red LEDs flash when the emergency shutdown is activated. So does the strobe, but this can be terminated with a switch.

From the module front one can trigger and reset the emergency shutdown, this can also be done from the Rack status panel. Or with Serial I/O system, using the Digital emergency interface module (DEIM). EMG consists of two 555 timers, one causes the big red LEDs to flash when triggered. The other is used as a reset delay, meaning that the reset button must be pressed for five seconds.


D-Sub 9-pin

  1. 12v+ in
  2. 12v- in
  3. 12v+ out
  4. 12v- out
  5. Reset switch input
  6. Trigger emergency shutdown input
  7. Emergency shutdown relay output
  8. Emergency shutdown LED output
  9. Emergency shutdown strobe output


Schematic drawing

Emg circuit.png

Parts list

Qty. Part
2 × Capacitor, aluminium electrolytic, 47 µF, 25V
2 × Capacitor, metallized polyester foil, 10 nF, (0.01 µF)
1 × D-sub soldering cups, 9 pin male
2 × DIL socket, 8-pin, 7.62mm
2 × Diode, rectifier, 1 A, 400V, 1N4004
2 × Diode, small signal, 1N4148/Ph
1 × Enclosure, plastic (1591), 112x62x31mm
2 × Fuse 5x20 mm, 2 A, fast-acting
2 × Fuse holder, open, PCB, 5x20mm
2 × Fuse holder, open, PCB, Protective cover
2 × LED 10mm, Red, 2.0V, 20mA
1 × LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10°
2 × LED 5mm, Red/Green, 2.0 2.1V, 10mA, 100 63mcd, 30°
3 × LED holder 5mm, RTC51, black plastic
2 × Mounting bracket, DIN rail, Plastic
32 cm2 PCB, stripboard, 100x160mm, 160cm2
2 × Relay, 2 CO, HJR1-2C, 12 VDC, 1A 120V, PCB
4 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
1 × Resistor, carbon film, 0.25W, 100 kΩ, 5%
5 × Resistor, metal film, 0.6W, 1 kΩ, 1%
1 × Switch, push-button, 1-pole, 1A, 50VAC, off-(on)
2 × Switch, toggle, 1-pole, micro, on-(on)
1 × Switch, toggle, 1-pole, micro, on-on
2 × Timer IC, NE 555, 0/+70 °C, DIL8
2 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B