Cat repeller circuit

With this cool cat/dog repeller circuit you could chase the cats  off  from any where you want. In fact, I designed this circuit to chase my cat from my computer table. Most of the animals like cats respond violently to ultrasonic sound and in fact it’s the best way to chase them off. This principle is employed in this circuit. The circuit here is nothing but an astable multivibrator wired around NE555 (IC1). The cat repellent circuit produces an ultrasonic sound in the range 15-20Khz. The NE 555 is enough to drive a small piezo buzzer and no amplification stages…

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Infrared motion detector circuit

Description. Here is the circuit diagram of an infrared motion detector that can be used to sense intrusions. Infra red rays reflected from a static object will be in one phase, and the rays reflected from a moving object will  be in another phase. The circuit uses this principle to sense the motion. The IC1 (NE 555)  is wired as an astable multivibrator. The IR diode connected at the output of this IC produces infrared beams of frequency 5Khz. These beams are picked by the infrared sensor, photo transistor Q1. At normal condition, that is, when there is no intrusion…

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Low cost fire alarm circuit.

Description. When there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC…

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Rain alarm circuit

Description. Here is a simple rain alarm circuit that produces an audible alarm when ever rain falls. The rain detector circuit is based on two transistors (Q1 & Q2) and a NE555IC (IC1). The two transistors are wired as a switch which goes on when the base of Q1 is shorted to the positive of the supply by the rainwater falling on the sensor. When the transistors are ON power supply is available to the IC1 which is wired as an astable multivibrator. The output of IC1 drives the speaker to produce an alarm. Do you need to learn more…

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Scoring game circuit

Description. A simple scoring game circuit that can be used for all occasions when a dice is needed.The circuit is based on a NE555 timer,a 74LS192 counter,a74LS247 decoder and a & segment LED display.The timer IC1 will produce the clock for the counter IC(IC2) whose frequency is determined by R1 and C2.When S2 is pressed the IC2 will count in up mode and when S3 is pressed the IC2 will count in down mode.The IC 3 will decode the count to display it on the seven segment LED display .Thats about the working of the circuit.The circuit is designed strictly…

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Aircraft radio circuit

Description. Here’s a low cost radio circuit that can be used to listen to the radio conversations between aircrafts. The radio circuit based on transistor 2N918 and diode 1N82 receives in the 220Mhz to 400Mhz range. Capacitor C1 and inductor L1 forms the tank circuit for tuning. Diode D1 performs the detection. Transistor T1 performs the necessary amplification. The out put audio signal is just enough to drive a small headphone. For driving speakers. Circuit diagram with Parts list.  Notes.  Use a 45cm long wire for antenna, For L1 make 2 turns of 22 AWG magnetic wire on a 5/32…

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Modified lamp dimmer circuit

Description. This is a modification of the circuit Simple Lamp Dimmer/Fan Regulator  previously  posted here. The working of the circuit is same as that of the previous, but in addition a snubber circuit consisting of resistor R4 and capacitor C3  is included to improve the performance of the triac T1. A fuse is also included for better safety. I think this is the better circuit to try . Circuit diagram with Parts list . Notes. No matter how  what ever may be the load lamp,fan , heater or anything it should be rated less than 200 Watts. No matter how …

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Two mode night light circuit

 Description. Here is a versatile night light circuit that can be used in two modes. The dimmer mode and a flashing mode. The circuit is based on dual opamp LM 358  and associated components. The first opamp IC1a is wired as a pulse generator and the second opamp is wired as a comparator. When the switch S1 is open the circuit is in dimmer mode where the intensity of the lamp can be varied by varying the POT R9. When the switch S1 is closed the circuit works in the flashing mode where the rate of flashing can be varied…

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3 W Stereo amplifier using MAX 7910

Description. A straight forward circuit diagram of a 3W stereo amplifier circuit using MAX 7910 IC is given here. This circuit is ideal for small power audio applications like portable CD players or radio sets. The circuit is designed strictly as per the datasheet and found to be working great. The MAX9710  a stereo audio power amplifier IC capable of delivering  3Watts  of out put to 4 Ohm loads. MAX9710 can be operated from a  single 4.5V to 5.5V power supply, makes it ideal for hand held applications. The IC also features thermal overload protection. Circuit Diagram with Parts list. …

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Battery Level Indicator

Simple Battery Level Indicator Description Here is a easy to build low battery level indicator circuit that produces a visible indication by flashing a LED when the battery voltage drops below a predetermined voltage.The circuit is based on Panasonic’s  IC MN13811G   and a efficient flasher based on transistors Q1&Q2.Here when the battery voltage drops below 2.4  V the output of the IC is activated and the flasher starts flashing.This circuit here is an ideal one for monitoring the level of all types of 3V batteries.The circuit is power efficient with a  idle current drawing as less as 1 uA  ,…

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