Wednesday, December 25, 2013
Best Electronic Crowbar Circuit Diagram for AC or DC lines
This is Best Electronic Crowbar Circuit Diagram for AC or DC lines. For positive protection of electrical or electronic equipment, use this against excessive supply voltage. Due to improper switching, wiring, short circuits, or failure of regulators, an electronic crowbar circuit can quickly place a short circuit across the power lines, thereby dropping the voltage across the protected device to near zero and blowing a fuse.
The triac and SBS are both bilateral devices, the circuit is equally useful on ac or dc supply lines. With the values shown for Rl, R2, and R3, the crowbar operating point can be adjusted over the range of 60 to 120 volts dc or 42 to 84 volts ac. The resistor values can be changed to cover a different range of supply voltages. The voltage rating of the triac must be greater than the highest operating point as set by R2, II is a low power incandescent lamp with a voltage rating equal to the supply voltage.
Best Electronic Crowbar Circuit Diagram for AC or DC lines
It may be used to check the set point and operation of the unit by opening the test switch and adjusting the input or set point to fire the SBS. An alarm unit such as the Mallory Sonalert may be connected across the fuse to provide an audible indication of crowbar action. (This circuit may not act on short, infrequent power line transients).
Sunday, December 22, 2013
Photodiode Alarm
This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.
Photo-Diode Alarm Circuit diagram
IR Transmitter Circuit diagram
A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.
Photo-Diode Alarm Circuit diagram
Thursday, December 19, 2013
Luggage Security System
While traveling by a train or bus, we generally lock our luggage using a chain-and-lock arrangement. But, still we are under tension, apprehending that somebody may cut the chain and steal our luggage. Here is a simple circuit to alarm you when somebody tries to cut the chain. Transistor T1 enables supply to the sound generator chip when the base current starts flowing through t. When the wire (thin enameled copper wire of 30 to 40 SWG, used or winding transformers) loop around the chain is broken by somebody, the base of transistor T1, which was earlier tied to positive rail, gets opened. As a result, transistor T1 gets forward biased to extend the positive supply to the alarm circuit. In idle mode, the power consumption of the circuit is minimum and thus it can be used for hundreds of travel hours.
To enable generation of different alarm sounds, connections to pin 1 and 6 may be made as per the table.
| Select 1 (Pin6) | Select 2 (Pin1) | Sound effect |
| X | X | Police siren |
| VDD | X | Fire-engine siren |
| VSS | X | Ambulance siren |
| “-” | VDD | Machine-gun sound |
Note: X = no connection; “-” = do not care
Source: http://www.ecircuitslab.com/2011/05/luggage-security-system.html
Subscribe to:
Posts (Atom)