Emergency power off controller — controlled by 555 timers

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

Details

This module will cut the main power to the Rack box if emergency power off is activated. The module is powered by a separate 12V supply; the emergency supply.

Main fuses are located on the module 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.

Two big red LEDs flash when the emergency power off is activated. An alarm output, used for a strobe, is also activated, but this can be disabled with a switch.

From the module front one can trigger and reset the emergency power off, this can also be done from the Rack status panel. Or with Serial I/O system, using the Digital emergency interface module.

The module uses two 555 timers, one makes the big red LEDs to flash when triggered. The other is used as a reset delay, requiring the reset button to be pressed for five seconds.

Video

Quick demo showing the operation of the emergency power off controller. First triggering, then resetting the emergency power off.

At 2:00 the rack box emergency power off is triggered and everything shuts down — then reset.

D-Sub 9-pin

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

Photos

Schematic drawing

Parts list

• 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