Digital Nocturnal Nuisance

Here is a fun project "digital nocturnal nuisance" which is quite amusing for both children as well as elder too. Digital nocturnal nuisance produces irritating sound in the absence of light.

Circuit Description of digital nocturnal nuisance

Digital nocturnal nuisance circuit is designed and fabricated around quad 2-input NAND gate IC and a timer 555 IC. LDR in this circuit is used as sensor.

Two trigger circuits of nocturnal nuisance are made from four NAND gates N1 & N2­ and N3 & N4 connected in series. Timer IC (IC2) is configured as oscillator and generate audio frequency.

High trigger due to low resistance (presence of light) of LDR at input of N1 switch on the transistor T1 as a result capacitor C1 discharge through R7. Due to this input at second trigger circuit becomes low. Similarly, when the low input due to high resistance across LDR (absence of light) turn of the transistor T1 and capacitor C1 get charged through resistor R7 and logic of second trigger circuit (N3 and N4) becomes 1 and high input is given to pin 4 of IC2 which produce irritating sound.

Preset VR1 is used to adjust the sensitivity and is so adjusted that the input of N1 are at logic zero when the light is off.

Capacitor C1 and C3 is act as time changing and tone changing component respectively of digital nocturnal nuisance.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 4.7 MΩ

R2, R6 = 10 MΩ

R3 = 10 KΩ

R4, R5 = 1 KΩ

R7 = 100 Ω

R8, R9 = 20 KΩ

R10 = 150 Ω

VR1 = 47 KΩ


C1 = 100 µF/16V

C2 = 100 nF

C3 = 15 nF


IC1 = CD4011 (quad 2-input NAND gats)

IC2 = NE555 (Timer IC)

T1 = BC108



LS1 = 8Ω speaker

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