Digital & Analog Based Mini electronics Projects Page_9

Digital & Analog Based Mini electronics Projects Page_9

81. Simple Digital Security System:

You can use this simple and reliable security system as a watchdog by installing the sensing loops around your building. You have to stretch the loop wires two feet above the ground to sense the unauthorized entry into your premises.

82. Simple Electronic Code Lock:

The circuit diagram of a simple electronic code lock is shown in figure. A 9-digit code number is used to operate the code lock.

83. Simple Low-Cost Digital Code Lock:

Many digital code lock circuits have been published in this magazine. In those circuits a

set of switches (conforming to code) are pressed one by one within the specified

time to open the lock. In some other circuits, custom-built ICs are used and positive and negative logic pulses are keyed in sequence as per the code by two switches to open the lock.

84. Skin Response Meter:

Human skin offers some resistance to current and voltage. This resistance changes with

the emotional state of the body. The circuit proposed here measures changes in

your skin resistance following changes in your mental state.

85. Sleep-Switch Cum Wake-Up Timer:

Here is a sleep-switch circuit that can be easily converted into a wake-up timer. A dual-mode time setting makes the system versatile. The circuit is low-cost and can function as a precise timer.

86. Smart Cell phone Holder:

This smart cellphone holder makes sure that you don’t forget to carry your mobile phone. Fitted in the car, it keeps searching for the mobile phone within the holder using infrared (IR) rays and alerts you through a flashing LED when it doesn’t find one. You can attach the circuit to your existing cellphone holder or, with a little skill, construct one as per your requirement.

87. Smart Hearing Aid:

Normally, hearing aid circuits consume battery power continuously once they are

switched on. The circuit given here saves battery power by switching on the sound amplifier section only when sound is detected. The sensitivity of the detection section and the ‘on’ time duration of the sound amplifier circuit can be set by the user. Also the circuit uses only a single condenser mic for sound detection and amplification.

88. Smart Water Level Controller:

In most houses, water is first stored in an underground tank (UGT) and from there it is pumped up to the overhead tank (OHT) located on the roof. People generally switch on the pump when their taps go dry and switch off the pump when the overhead tank starts overflowing. This results in the unnecessary wastage and sometimes non-availability of water in the case of emergency.

89. Sound Trigger Lamp:

You can take this white LED based night lamp on your picnic outings. The lamp has sound trigger and push-to-on facilities and gives ample light during a walk at night. It will also prove useful in locating the door of your tent in the darkness. A click of the fingers will switch on the lamp for three minutes to help you in a strange place.

90. Speed Control Of Dc Motor Using Pulse-Width Modulation:

Pulse-width modulation (PWM) or duty-cycle variation methods are commonly used in speed control of DC motors. The duty cycle is defined as the percentage of digital ‘high’ to digital ‘low’ plus digital ‘high’ pulse-width during a PWM period. 5V pulses with 0%

through 50% duty cycle.