Cash box guard

Key Attributes.

The cash box guard circuit is built around IC CD4060 (IC1), which has an inbuilt oscillator and divider. The basic oscillator is configured by a simple resistor-capacitor (R-C) network. IC CD4060 divides this oscillator frequency into binary divisions, which are available as outputs. If cash box is closed, the interior will be dark. Hence in the dark, the lightdependant resistor (LDR1) resets IC1 and it stops oscillating and counting. At the same time, pins 13 and 14 of IC1 go low. So neither the piezobuzzer (PZ1) sounds, nor the relay (RL1) energises, indicating that the cash box is closed. If someone tries to open the door of the cash box, light—most probably from the burglar’s pen torch—falls on LDR1 fitted into the cash box. As a result, LDR1 conducts and pin 12 of IC1 goes low. IC1 starts oscillating and counting. With the present timing R-C components (at pins 9, 10 and11), the output timing at pin 14 of IC1 is two-three seconds. Hence pin 14 of IC1 goes high so the piezobuzzer (PZ1) sound.