door alarm timer

Discussion in 'The Projects Forum' started by curlerhaus, Mar 6, 2009.

  1. curlerhaus

    Thread Starter New Member

    Mar 6, 2009
    I work in a research lab with several freezers. One of our freezers was left open last night. Some of our samples are ruined. I am looking for a door alarm on a timer. If the door is left open for more than 5 minutes an alarm will sound. I haven’t been able to find an item to purchase that fits my needs. Anyone know of a circuit to build?
  2. Bernard


    Aug 7, 2008
    Just a start: Use a NO door switch to connect a battery to a 555 IC 5 min timer and a piezo buzzer. When door is opened ,timer starts, if door is not closed within 5 min, timer output will go low, activating buzzer. How loud does buzzer need to be?
  3. Oxbo Rene

    Active Member

    Feb 20, 2009
    Here's a couple pics of my mailbox door alerter circuit I made awhile back (10 yrs ago).
    "Deep Space" is just a Co name I made up, etc..
    I used half of a 556, you could just use a 555.
    Anytime the mailbox door is opened, the piezo chime goes off every 60 sec till reset. Can turn circuit off if need be for whatever purpose...
    Have changed the names to "freezer" for ya to better grasp the concept, etc...
    Will need to put 5-min timer in front of it, etc.....
    Last edited: Mar 8, 2009