Power supply and fuse monitoring module

From CaveLab
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This module was part of the rack box project — which was terminated when I moved out of my first apartment.
MMU installed in the Rack box

This unit monitors all necessities in the Rack box. It gives an alarm if a power supply should fail, a fuse burn out or if Serial Server times out (via. Online serial interface device). 5, 12 and 24V, positive and negative, is connected to optoisolators inside the MMU. The 24V uses en external optoisolator. It will detect if a main fuse burns out or a power supply is lost. MMU is bypassed the main fuses, but if the 12V supply is totally lost MMU will also lose power. Fuse errors is detected by the fuse module Fuse box 1, and the signal sent to MMU which gives an alarm and notifies other modules. Serial Server monitoring is based on the same principles that Module stability monitoring unit 2 operates on, a lifesignal is sent ever X second. And if this signal fails to come a timeout alarm will sound. The lifesignal from Serial Server is only sent every 60 seconds, and it takes 310 for the timeout alarm to sound. Online serial interface device is the serial module delivering the lifesignal, so if this module fails this will be detected as a server timeout.



  1. Server lifesignal
  2. Fuse error
  3. Emergency supply failure (see Emergency shutdown unit)
  4. 5V supply
  5. 12V supply


  1. Buzzer (not in use)
  2. Error signal (to Signal and lights controlling unit)
  3. Fuse error LED
  4. Supply failure LED
  5. Lifelight (built-in LED)
  6. Lifesignal (to Module stability monitoring unit 2)
  7. Server timeout LED


  • Yellow 12V+
  • Blue 0V
  • Black Server lifesignal (in)
  • Red Fuse error (in)
  • Purple Emergency supply failure (in)
  • Green 5V+ supply (to optoisolator)
  • White 5V- supply (to optoisolator)
  • Orange 12V+ supply (to optoisolator)
  • Brown 12V- supply (to optoisolator)
  • Green Buzzer (out)
  • Yellow Error signal (out)
  • Orange Fuse error (out)
  • Grey Supply failure (out)
  • Brown Lifesignal (out)
  • Cyan Server timeout (out)

Alarm situations

  • Server timeout (310 sec)
  • Emergency supply failure
  • 5V supply failure
  • 12V supply failure
  • Fuse error

Source code

Bascom-AVR source is available in a git repository:


Schematic drawing


Parts list

Qty. Part
1 × AVR AT90S2313-10PI, DIL-20, 10 MHz, 15 I/Os
1 × Capacitor, aluminium electrolytic, 10 µF, 25V
2 × Capacitor, aluminium electrolytic, 22 µF, 25V
2 × Capacitor, ceramic, 22 pF, 100V
1 × DIL socket, 20-pin, 7.62mm
2 × DIL socket, 6-pin, 7.62mm
1 × Enclosure, plastic (1591 FL), 150x80x50mm, flange
2 × Fuse 5x20 mm, 400 mA, fast-acting
2 × Fuse holder, open, PCB, 5x20mm
1 × LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10°
1 × LED holder 5mm, RNG 268, Fixing ring
2 × Optocoupler, single, CNY17F-3, DIL-6
128 cm2 PCB, stripboard, 100x160mm, 160cm2
1 × Quartz crystal oscillator, 4 MHz
5 × Resistor, carbon film, 0.25W, 330 Ω, 5%
9 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
5 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
3 × Resistor, metal film, 0.6W, 1 kΩ, 1%
1 × Switch, push-button, PCB, 1-pole, H4.3mm, vertical, black
1 × Terminal block, pluggable, 3.5 mm, 2-pin screw female
1 × Terminal block, pluggable, 3.5 mm, 2-pin vertical male
1 × Terminal block, pluggable, 3.5 mm, 4-pin screw female
1 × Terminal block, pluggable, 3.5 mm, 4-pin vertical male
8 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B
1 × Voltage regulator +5V, 2 A, L78S05CV