Night dog barking anti-theft reminder circuit

The inspiration for designing this reminder circuit comes from the pet dog at home, which starts barking continuously when it detects a moving shadow. Dogs have the ability to adaptively improve their visual sensitivity at night with low light, especially for moving objects. If the moving shadow is a night thief, it is just right to use it to make an anti-theft reminder using dog barking.

When a dog barks, the sound of the dog barks through the microphone to connect a circuit to a lighting lamp, which lights up for a period of time to remind the owner of the house that there may be a burglar breaking in at night.

The condenser microphone is installed in the dog house to detect the dog's barking and generate an AC signal. This AC signal is sent to the base of transistor T1 through the DC blocking capacitor C1. After T1 and T2 amplify the sound signal, a current pulse is sent out at the collector of T2.

This trigger pulse is added to the collector of T3 and sent to T4 through coupling capacitor C3, making T4 cut off. The high potential of the collector of T4 makes T3 forward-biased through R8. After T3 is turned on, C3 starts to discharge, making T4 continue to be cut off. The cut-off state of T4 is maintained until C3 is fully charged to make T4 conductive.

After T4 is turned on, its collector voltage becomes low, making T3 enter the cut-off state. R9 and C3 are both timing components. After C3 is fully charged, its discharge time is about 2 minutes.

Therefore, when a dog barks in front of the microphone, the bidirectional thyristor BT136 is turned on and the bulb lights up for about 2 minutes, which is enough to alert the homeowner.