Pendulum Intermitent Alarm (ART016E)

The circuit can be used to protect cars and other large objects, the home, and other items, as the sensor can be used to detect any kind of movement. You can also use this circuit to detect movement in scientific experiments.

The relay can drive powerful warning systems such as sirens, horns lamps, and so on.

The circuit can be powered from common cells batteries, and current drain is very low (about 5 mA) when the relay is off.

A schematic diagram of the Pendulum Intermittent Alarm is given in Fig. 1.

Figure 1 – Schematic diagram of the alarm

The relay coil is chosen to match the power supply voltage. You can use a mini DPDT, 1 A relay, Radio Shack 275-249 or, for heavy loads, a 10 A mini SPDT relay, Radio Shack 275-248.

These relays are rate to12 V and drain only 38 mA (coil resistance = 320 Ω).

The turn-on and turn-off frequency is determined by R3 and C1. You can vary the values of these components to alter the intermission rate.

Values can range as shown in the schematic diagram.

Reset is made by a touch switch, but you can also replace this sensor with a common SPST momentary switch.

Proper positioning of the polarized components (diode and electrolytic capacitor) should be observed.

The sensor’s details are shown in Fig. 2.

Figure 2 – Details of the sensor

Note that operation occurs when the vertical bare wire touches the ring due any Vibration.