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FM Transmitter Bug 2008-02-07 05:32:00 This small transmitter uses a hartley type oscillator. Normally the capacitor in the tank circuit would connect at the base of the transistor, but at VHF the base emitter capacitance of the transistor acts as a short circuit, so in effect, it still is. The coil is four turns of 18swg wire wound around a quarter inch former. The aerial tap is about one and a half turns from the supply end. Audio sensitivity is very good when used with an ECM type microphone insert. David's email : radio_david@yahoo.comSource: Read more:Transmitter
Smart Phone light 2008-02-07 05:30:00 The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light
during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all. If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1). The first part of the circuit functions as a ring detector. When telephone is on-hook, around 48V DC is present across the TIP and RING terminals. The diode in the opto-coupler is ‘off’ during this condition and it draws practically no cur Read more:Smart
Soft Musical Telephone Ringer by UM66T 2008-02-07 05:22:00 The incoming ring is detected by transistor T1 and components wired around it. In absence of ringing voltage, transistor T1 is cut off while transistor T2 is forward biased as resistor R2 is returned to the positive supply rails. As a result collector of transistor T2 is at near-ground potential and hence IC1 (UM66) is off. Also capacitor C2 is charged to a slightly positive potential. During positive half of the ringing voltage, diode D1 forward biases transistor T1 and rapidly discharges capacitor C2 to near ground potential and cuts off transistor T2 which, in turn, causes IC1 to be forward biased and music signal is applied to base of transistor T3 which drives the speaker. During negative half of the ringing voltage, capacitor C2 cannot charge rapidly via resistor R2 and hence transis Read more:Musical
Time Delay Relay II by IC 4011 2008-01-06 09:25:00 When activated by pressing a button, this time delay relay will activate a load after a specified amount of time. This time is adjustable to whatever you want simply by changing the value of a resistor and/or capacitor. The current capacity of the circuit is only limited by what kind of relay you decide to use.Read More Source: you. Read more:Delay
Time Delay Relay by 555 2008-01-06 09:19:00 A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. The time is adjustable from 0 to about 20 seconds with the parts specified. The current capacity of the circuit is only limited by what kind of relay you decide to use.Read More Soure you. Read more:Delay
LM3647 Reference Design 2008-03-17 04:43:00 The LM3647 provides a single-chip charge management solution for Nickel Cadmium, Nickel Metal Hydride and Lithium-Ion cells. The device handles the entire charging process from rejuvenating deeply discharged cells to providing a number of charge termination and maintenance options. The LM3647 Demo Board allows users to create a battery charging solution with little effort.Link : -1165.pdf
7,2 Volt Field Charger 2008-03-17 04:41:00 The unit is novel as it’s display graph shows you the time the battery has been charging in 2 minute intervals up to 16 minutes when finished. The “power” led indicates source voltage as it dims, and goes out at 11 vdc, this is needed because the unit draws 20 amps fully charging 4 batteries as you will need to run your engine or you will walk home!!Link : ~antoon/circ/7.2V-Charger
.pdf Read more:Field
Low-Cost Anemometer Fights Dust 2008-06-26 13:33:00 This application note describes a low-cost circuit that can detect when a chassis fan filter has become clogged with dust. It does this by using a temperature sensor to determine the rate of cooling of a transistor in the air path of the cooling fan, thereby implementing a simple thermal anemometer.source: Read more:Fights
LX1970 VISIBLE LIGHT SENSOR 2008-06-26 13:29:00 The LX1970 light sensor can be used in conjunction with an LCD Front or Back Light Controller such as the LX1992 for LEDs or the LX1689 for CCFLs. This application note describes how to design in the LX1970.Source:
AM portable radio receiver by ZN414 IC 2008-06-21 09:14:00 An AM portable radio receiver
made from the ZN414 IC. The ZN414 ic has now been replaced by the MK484 which is identical in performance and pinout.Read More
Micro Power AM Broadcast Transmitter 2008-06-21 09:11:00 In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable (VFO) with a capacitor/resistor combination. A 100pF capacitor is used in place of the crystal for VFO operation. Amplitude modulation is accomplished with a s Read more:Broadcast
, Transmitter
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