Here we have an interesting version of a temporized alarm which can use the most diverse types of sensors. Once activated it keeps triggered an alarm circuit for a time set in P1. This time can range from a few seconds to about 20 minutes depending on the value of C2 which at most can have 470 µF and P1 which at most can have 1 M.
See the formula for the first temporized alarm that is the same for this circuit. (See the formula in the math section of the site)
The device is powered by 4 medium or large alkaline batteries and in standby condition its power consumption is very low.
The complete circuit is given in Figure 1.
![](/images/sampledata/artigo2017/min0097_0001.png)
One touch at the pressure switch (NO) and the alarm will fire for a time depending on the setting of P1.
For S1 we can use a switch coupled to doors or windows, a reed-switch that in this case is activated by the approximation of the magnet and not by its withdrawal or even a pendulum sensor, as shown in Figure 2.
![](/images/sampledata/artigo2017/min0097_0002.png)
The alarm also allows the connection of sensors in parallel, each of which can activate the alarm independently.
In Figure 3 we give the printed circuit board.
![](/images/sampledata/artigo2017/min0097_0003.jpg)
CI-1 - 555 - integrated circuit
D1-1N4148 or 1N914 - silicon diode of general use
K1 - 6 V relay
P1 - trimpot or potentiometer of 100 k
S1 - pressure switch or sensor
S2 - single switch
B1 - 6 V - 4 medium or large batteries
C1 - 470 nF (474) - ceramic capacitor
C2 - 100 µF X 12 V - electrolytic capacitor
R1 - 22k X 1/8 W - resistor (red, red, orange)
R2 - 10k X 1/8 W - resistor (brown, black, orange
Miscellaneous:
A printed circuit board, connection wires, assembly box, support for 4 alkaline batteries, etc.