Delayed delivery of the signal to the reed switch in the Chinese mini alarm

I got into the hands of the Chinese mini alarm that is installed on the door, or windows and triggered instantly when they are opened (a photo 1). My task was, to create a start-up delay siren about 10 seconds. Since I was going to put it on the front double doors.

A photo 1

The alarm unit is mounted on the first doors and after opening them I have 10 seconds to open the second door. For the owner of the apartment this time is enough, and for thieves of this period it may seem a little. Of course, it will not fully protect your apartment, but still for little money you can get a little extra security.

Miscellaneous Delay Solution, using delay relay, integrated timers, microcontrollers, etc.. But this is not worth the big investment, and even more so it’s not very rational to pile up the circuit, that will pull the body increase alarm.

The droplet microcircuit did not make it possible to find its characteristics in datasheets. But seeing, that a weak constant voltage is applied to the reed switch from the integrated circuit, an unambiguous decision was made. To delay on, use an electrolytic capacitor, which connects parallel to the reed switch. The scheme of this connection is shown in the figure. 1.

rice. 1

In my case, the resistor 47 kohm and capacitor 22 uF. Such a capacitor gives a time delay of about 10 with. With an increase in the capacitance of the capacitor, the signal delay time will be proportionally increased.

A photo 2

The capacitor in place with a resistor connected by a hinged installation and easily fit in the free space of the mini alarm case (a photo 2).


  1. Borrowed. How to increase the delay? I put the capacitor on 100 uF and not working…

  2. Simple question, and what does the reed switch look like on this board, I have a similar device, but out of 2 parts, none of them react to the brought up magnet ..?

    • Hercone (acronym for "sealed contact") - electromechanical switching device, changing the state of a connected electrical circuit when exposed to a magnetic field from a permanent magnet or external electromagnet, For example, solenoid.
      Reed switch

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