Missing Pulse Detector Circuit

Posted by Micro System

on Tuesday, September 14, 2010

This is a circuit for missing pulse detector circuit that can be used to detect missing pulses in an incoming pulse train. The main component of this circuit is the 555 timer IC.  In this circuit, it is configured as a mono stable multi vibrator, i.e., a circuit which will output a single pulse every time it is 'triggered'. This is the figure of the circuit;

Every time a pulse arrives at pin 2 of the 555 timer in this circuit, the 555 is triggered to output a single pulse at pin 3. The width of this output pulse is defined by the values of R2 and C1.  R2 and C1 must be chosen such that the output pulse width is slightly greater than the time between each incoming pulse.  If the arrival of the pulses at pin 2 is continuous, the output will never complete a single pulse.  This is because the 555 timer will always be retriggered and C1 will always be discharged through Q1 every time a new input pulse arrives.  As such, the output of pin 3 will always be 'high'. However, a missing pulse will allow pin 3 to output a complete pulse.  This means that it will change its state from 'high' to 'low' after the set pulse width has been attained. Thus, a change in state of the output of this circuit signifies that it has detected a missing pulse in the pulse train arriving at the input.

Lightning Detector Circuit Using Transistor

Posted by Micro System

on Tuesday, August 17, 2010

This is a circuit for lighting detector circuit that is using a VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning. A bright lamp flashes in synchronize with the lightning bolts indicating the proximity and intensity of the storm. This is the figure of the circuit;

This circuit is the simple receiver which consists of a tuned amplifier driving a modified flasher circuit. The flasher is biased to not flash until a burst of RF energy, amplified by the 2N3904, is applied to the base of the 2N4403. The receiver standby current is about 350 micro amps which is nothing at all to a couple of D cells, hardly denting the shelf life. Of course, the stormier it gets, the shorter the battery life.

Adjust the potentiometer until the regular flashing just stops. (Use a multi-turn trimmer.) When properly adjusted, the lamp will occasionally flash when large motors or appliances switch on and off and an approaching storm will give quite a show. Obviously, tune-up is a bit more difficult during stormy weather. Adjust the pot with no antenna if lightning is nearby. Tune an AM radio to the bottom of the dial to monitor the pulses that the lightning detector is receiving. This lightning detector is not so sensitive that it will flash with every crackle heard on the radio but will only flash when storms are nearby. Increased sensitivity may be achieved by increasing the antenna length. The experienced experimenter may wish to add another gain stage after the first by duplicating the 2N3904 circuitry including capacitor coupling with the addition of a 47 ohm emitter resistor to reduce the gain somewhat.

Electric Field Detector Circuit Using 6 Million Gain Transistor

Posted by Micro System

on

This is a circuit that can produce 6 million gain. As well as detecting general electric noise, this circuit can be used to detect “mains hum,” the presence of your hand without any direct contact, and detect static electricity. This circuit is based on transistor BC547. This is the figure of the circuit;

The mains cable can be located by this circuit by moving it across any wall. The gain is achieved from 200 x 200 x 200. Since the circuit detects very weak electric field, it might look like ghost detector because electric field has weird pattern sometimes.