Alarm disabling unit for production equipment with long stop warning

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.

I built this module for Sensonor ASA back in 2007, I have no idea if it is alive today.
ADU installed on equipment

The purpose of this module is to make it possible to the operator to reset the alarm on the production equipment, but still make sure that the alarm sounds at the next fault. Today there is no way to turn off the alarm until the situation is cleared, but with this module that is now possible. Earlier the operators would remove the relay for the alarm, this gave an unfortunate long stop time if the relay was not placed back and the equipment faulted silently.

The production equipment has two chambers with controlled temperature, when the equipment stops the temperature in the cold chamber becomes unstable. When the emergency shutdown is triggered, this is needed for accessing the guard doors, the LN2 (liquid nitrogen) supply is closed. Therefor one doesn't want the equipment stopped for too long.

Alarm reset

When a alarm situation occurs the red LED flashes and the production alarm sounds, by pressing "reset alarm" the voltage to the sound alarm is cut. The red LED lights continuously when the alarm is reset. When the alarm situation is no more the red LED turns off and the voltage to the sound alarm is restored. When a new fault occurs the procedure is repeated.

Warning long stop

If an alarm situation persists more then 30 or 60 minutes (jumper setting) the module will sound the alarm again. That means if the previous alarm was reset the voltage to the sound alarm will now be restored, blue LED starts flashing. This alarm is reset the same way, by pressing "reset alarm" the voltage to the sound alarm relay is once more cut. The blue LED will now be on continuously. The purpose of this alarm is to make the operators aware that they should consider defrosting the cold chamber is the equipment is left in standby much longer.



  1. PD.0 Reset button
  2. PD.1 Stack lights signal
  3. PD.2 Jumper for setting long stop timer


  1. PB.0 Red LED
  2. PB.1 Blue LED
  3. PB.2 Stack lights relay N.O
  4. PB.3 Power LED

D-Sub 9-pin

Pin Function Color
1 24V Red
2 0V Black
3 Stack lights in + (to optoisolator) Green
4 Stack lights in - (to optoisolator) Blue
5 Stack lights relay + Yellow
6 Stack lights relay - N.O White


Panel front


Inside equipment


Schematic drawing


Internal connectors


  1. GND to internal reset button (Without resistor)
  2. Signal from internal reset button (With resistor)
  3. GND to stack lights relay (D-sub 6)
  4. Signal from stack lights
    • Red : + (D-sub 3)
    • Blue : - (D-sub 4)
  5. 24V supply voltage
    • Red : + (D-sub 1)
    • Blue : - (D-sub 2)
  6. 24V to stack lights relay (D-sub 5)
  7. Jumper for setting long stop timer
    • With jumper : 30 min
    • Without jumper : 60 min

Source code

Bascom-AVR source is available in a git repository:


Parts list

Qty. Part
1 × AVR ATtiny2313-20PU, DIL-20, 20 MHz, 18 I/Os
1 × Capacitor, aluminium electrolytic, 10 µF, 25V
2 × Capacitor, aluminium electrolytic, 47 µF, 25V
1 × Capacitor, ceramic, 1 nF, 100V
2 m Control cable, 8-cores, shield, 0.14mm2, 250 V, Ø 5.1mm
1 × D-sub plastic hood, 9-pin, black
1 × D-sub soldering cups, 9 pin female
1 × D-sub soldering cups, 9 pin male
1 × DIL socket, 20-pin, 7.62mm
1 × DIL socket, 6-pin, 7.62mm
1 × Diode, rectifier, 1 A, 400V, 1N4004
1 × Enclosure, plastic (1591 FL), 150x80x50mm, flange
1 × Fuse 5x20 mm, 400 mA, fast-acting
1 × Fuse holder, open, PCB, 5x20mm
1 × Fuse holder, open, PCB, Protective cover
1 × Heat conducting film for heatsink, Adhesive, TO220
1 × Heatsink, 15K/W @ 4W, 28mm 7g, TO220
1 × Jumper, 2.54mm
1 × LED 5mm clear, Blue, 3.4V, 20mA, 7.200mcd, 20°
1 × LED 5mm clear, Red, 2.1V, 20mA, 7.000mcd, 20°
1 × LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10°
1 × LED holder 5mm, RTC51, black plastic
1 × LED lens 5mm, CLF 280, Blue
1 × LED lens 5mm, CLF 280, Red
1 × Optocoupler, single, CNY17F-3, DIL-6
1 × Resistor, carbon film, 0.25W, 100 Ω, 5%
1 × Resistor, carbon film, 0.25W, 150 Ω, 5%
4 × Resistor, carbon film, 0.25W, 330 Ω, 5%
2 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
3 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
1 × Resistor, metal film, 0.6W, 2.2 kΩ, 1%
8 × Straight pin header, female, Single row, 2.54mm
10 × Straight pin header, male, Single row, 2.54mm
1 × Switch, push-button, 1-pole, 1A, 50VAC, on-(off)
1 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B
1 × Voltage regulator +5V, 1 A, 7805PI