Digital & Analog Based Mini electronics Projects Page_8

Digital & Analog Based Mini electronics Projects Page_8

71. Power-Supply Failure Alarm:

Most of the power-supply failure indicator circuits need a separate power-supply for themselves. But the alarm circuit presented here needs no additional supply source. It

employs an electrolytic capacitor to store adequate charge, to feed power to the

alarm circuit which sounds an alarm for a reasonable duration when the mains

supply fails.

72. Precision Digital Ac Power Controller:

SCRs and Triacs are extensively used in modern electronic power controllers—in which power is controlled by means of phase angle variation of the conduction

period. Controlling the phase angle can be made simple and easy if we set different firing times corresponding to different firing angles. The design given here is a synchronized programmable timer which achieves this

objective.

73. Programmable Timer For Appliances:

This programmable timer is useful for domestic, commercial as well as industrial applications. It automatically turns the appliance on/off after a preset time. The time period can be varied from 8 seconds to 2 hours with the help of rotary switches S2 and S3.The circuit works in two modes: off mode and cyclic mode. Slide switch S4 is used

for mode selection.

74. Pulse Generator:

This circuit is very useful while checking/operating counters, stepping relays, etc. It avoids the procedure of setting a switch for the required number of pulses. By pressing appropriate switches S1 to S9, one can get 1 to 9 negative- going clock pulses, respectively.

75. Safety Guard:

Protect your home appliances from voltage spikes with this simple time delay circuit.

76. School college Quiz Buzzer:

Manual buzzers used for quiz competitions in schools and colleges create a lot of confusion in identifying the first respondent. Although there are circuits using PCs and discrete ICs, they are either too expensive or limited to only a few number of players.

77. Shadow Alarm:

This opto-sensitive circuit sounds an alarm whenever a shadow falls on it. So it can be used at night by shopkeepers to protect the valuables in their showrooms. A dim lighting in the room is necessary to detect the moving shadow. Unlike opto-interruption alarms based on light-dependent resistors (LDRs), it does not require an aligned light beam to illuminate the photo-sensor.

78. Short-Circuit Protection In Dc Low-Voltage Systems:

Many a times you need to power an adjoining accessory circuit from the power supply used in the main module circuit. Here is a circuit to derive the additional power supply from the main circuit. The main circuit is protected from any damage due to short-circuit in the additional power supply circuit by cutting off the derived supply voltage. The derived supply voltage restores automatically when shorting is removed.

79. Shutter Guard:

This sensitive vibration sensor is exclusively made for shops to protect against burglary. It will detect any mechanical or acoustic vibration in its vicinity when somebody tries to break the shutter and immediately switch on a lamp and sound a warning alarm. A 15-minute time delay after switch-on allows sufficient time for the shop owner to close the

shutter.