The kit can be used to make a shed or room alarm. It is armed / disarmed by a hidden switch. Alarms are detected by a micro switch mounted onto a door. A timer provides an entry delay during which the system can be disarmed, whilst a separate timer silences the alarm after two minutes. Both of these timers are implemented via a 555 timer IC.
The alarm can be further enhanced by using a simple key switch for arming / disarming or by adding a magnetic door contact to activate it. The board, battery pack & buzzer can be placed into a box designed by the student.
Kit contents:
- 1 x PP3 clip lead
- 1 x 4AA battery holder
- 1 x slide switch
- 1 x 556 (dual 555) timer IC
- 1 x 14 pin IC holder
- 1 x Piezo buzzer
- 4 x 10nF capacitor, ceramic
- 2 x 100uF capacitor, electrolytic
- 1 x 330ohm resistor
- 3 x 10Kohm resistors
- 1 x 220Kohm resistor
- 2 x 1.2Mohm resistors
- 1 x micro switch
- 1 x 5mm red LED
- 0.5m connecting wire
- 1 x Alarm PCB
PSB dimensions: 51mm x 41.5mm.
Requires x4 AA batteries, available separately.
Click here to download build instructions 
Note: Schools will receive a more detailed set of teaching notes on a CDROM.
