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100 Seconds Duration On Switch with Touch Control
This is a touch control switch which keeps the circuit on about 100 seconds after touching the plate connected to the 2 numbered pin. At the end of this time duration, relay releases and the circuit gets to off position.
The impedance of the trigger input of the 555 timer IC is very high and the inductive voltage on the human body is enough to trigger it. The circuit works based on this principle. You can use a piece of metal as a plate. The circuit can be used in toy circuits, buzzers or any project that is suitable. You can adjust the duration time by changing the R1 and C1 values.
100KHz Crystal Oscillator
There is a great deal of old amateur gear which many amateurs have decided to restore and bring back to life. While much of the early amateur transceivers work just fine they usually lack a digital readout and must rely on analog dials for tuning. The problem of dial calibration is complicated by the non-linear effects of tuning capacitors. This month's circuit is a 100Khz crystal calibrator using an inexpensive microprocessor crystal and CMOS IC's which are readily available at Radio Shack.
The main problem with building a 100Khz oscillator is the unavailability of 100Khz crystals. Even if you find a vendor willing to cut such a crystal for you, plan on paying $20 or more not including shipping charges. The circuit uses an inexpensive 8MHz microprocessor crystal which can be easily obtained from most parts suppliers. Using a 74HCT393 binary counter IC, we can easily divide down the 8 MHz signal from our crystal into 100Khz or almost any frequency we need.
5 - 30 Minute Timer
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps. Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type.
A Simple BFO Metal Detector
A Very Simple "Beat Frequency Oscillator" type of Metal Detector.
These are about the Simplest of all Metal Detector types,
But still quite useful for many Detecting applications.
And although this one is particularly simple, I find it works very well.
For use outside on the ground the coil "MUST have a Faraday Shield", or it will not be of any use because of Ground Effects.
AC Power Meter
If you attempt to save power in the house thoroughly, you can not ignore the standby power consumption of appliances. We made a device to measure the power consumption of appliances. Actually, to say the AC power meters measure the 100V AC current is flowing in the power cord over do it. In general, the voltage is measured casually, is difficult to measure the current. To cut off a part of the circuit current flow from a current meter must be connected to it.
AC-AC Solid State Relay or SSR
This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this. A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC control signal is available. The BTA series has the heatsink tab insulated from the Triac chip inside. The BTB needs electrical insulation to the heatsink.
Alarm Sounds When Refrigerator Door Remains Open Too Long
Not properly closing a refrigerator door will no doubt invite huge electricity bills. This gadget is an alert device that beeps if you leave the refrigerator door open for more than 20 seconds. When the door opens, the lamp illuminates and the IC (a 4060B counter/oscillator) starts counting down. After a preset delay of 20 seconds, the piezoelectric buzzer beeps intermittently for 20 seconds and then stops for the same amount of time. This cycle repeats until the refrigerator door closes.
Animated Christmas Star
The star is about 35cm across and designed to be displayed indoors in a window.
I originally created the star three years ago using a 16F872 controller. The original version worked ok - but had no spare memory for adding more features.
This new version uses a 18F2620 because I now prefer the 18F series and decided it would be a good general purpose 28 pin chip to use. It has more than enough memory (64K) so I can add as many features as I want now.
(It should also work using a PIC18F2525 instead if you find it easier or cheaper to obtain)
Since, I made the first version, brighter LEDs are now available and cost is much lower - this project currently uses a total of 60 comprising of 25 Blue, 15 Green and 20 Red.
Anti Theft Car Wireless Alarm
This is anti theft alarm with wireless connectivity ,called Anti Theft Car wireless alarm The FM radio-controlled anti- theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park.
Automatic Fan Controller Circuit
This circuit will turn on/off 12V DC fan or CPU fan when temperature above normal temperature.You can set turn on temperature by adjust VR1. This circuit use an NTC (Negative temperature coefficient)which is a thermistor is one in which the zero-power resistance decreases with an increase in temperature. So If temperature increase the voltage at pin 3 on LM311 will decreased .The resistance of NTC is about 10K at 25'c.