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This simple circuit generates acoustic and visual alarms when it detects a shock, vibration or earthquake.

English description below

Deze schakeling geeft een optisch en akoestisch signaal bij een aardbeving of een schok. De schakeling bestaat uit een opnemer, een pulsverlenger, een signalering en een relais. Met het relais kan men div. apparaten schakelen. Ook kan men hiermee de event zender en ontvanger bedienen. Als voorbeeld kan de aardbevingsdetektor op een moeilijk te bereiken plaats gemonteerd worden en draadloos de aardbeving "doorgeven".

 

Earth quake/shock detector

Without trigger from the sensor the output of the opamp will be low, this level is also found on the input of the pulse stretcher built from IC2A..D. The output of this pulse stretcher is also low then, C1 discharged and the outputs of IC2A, B and D are at logic high level. When the shock sensor generates a pulse, the output of IC2C goes high by IC2B and stays high as long as C1 is not charged to the voltage level where the output of IC2A switches low. As soon as this level is reached, pin 12 of IC2D is pulled down via R3 (the output of IC2D will go high), and also the output of IC2B goes high, and the pulse stretcher is back in its stable state. The next pulse from the sensor can trigger the stretcher when C1 is discharged.

Diode D3 and resistor R3 ensure that for pin 12 (IC2D) a logic high on the output of IC2A has priority over the level on the output of the pulse stretcher (pin 8 of IC2C).

The 3V battery power supply is controlled with a normally-closed push button, so the ‘alarm’ can be switched off (hard reset) with this switch.

An LED-indicator (R5/LED1), acoustic alarm (Bz1) plus relay RE1 at the output  may be a bit overdone, for most applications one or even two of these options can be omitted.

On the PCB layout two switch contacts are shorted, this was done on purpose to give some more options to find a suitable relay. In most cases the ‘normally-closed’ contact of a relay is positioned closest to the coil, followed by the common and ‘normally-open’. The author used a relay (American Zettler AZ822) with the ‘normally-closed’ and common contacts swapped, both contact arrangements will work on this PCB.