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Homemade Metal Detector
Posted on Wednesday, May 4, 2011   •   Category: Sensors


Nowadays, metal detection has become a hobby of many people. Besides as a funny and interesting hobby for them, they also wished indeed a treasure that is embedded in the soil when excavated. For this one hobby, you have to have a tool known as a metal detector. To undergo this hobby is quite expensive to buy. But for those of you who want to try to make yourself a metal detector, the following will be presented a simple schematic that relates to metal detection. The operation of metal detector is based on superheterodying principle, which is generally used in a heterodyne receiver. This circuit uses two RF oscillators. Both oscillator frequency is fixed at 5.5 MHz. The first RF oscillator comprises transistor T1 (BF 494) and 5.5 MHz ceramic filter commonly used in TV sound-IF section. The second oscillator is an oscillator Colpitt realization with the help of the transistor T3 (BF494) and inductor L1 (follow the details of construction) was driven by trimmer capacitor VC1.


Studio Stereo Headphone Amplifier
Posted on Tuesday, May 3, 2011   •   Category: Headphone Amplifiers


This is a dual/stereo headphone amplifier with high quality audio built around OPA2134. This headphone amplifier can drive high or low impedance phones with low noise and distortion. When used with line level signals from CD/MP3 players, etc., requiring only a power supply and volume potentiometer. Many high-power amplifier audio designs have already provided an output for headphones. To support simple headphones, additional circuitry is required by adding only two resistors in series with the loudspeaker output to limit the drive current and protects the phone that in terms of reinforcing failure. Considering its simplicity, this scheme works well resistive limit, although it will cause distortion if the load is non-linear - a prospect that may be most headphones. In addition to eliminating potential sources of distortion, there are a number of other reasons why you might consider to build a separate headphone amplifier.


ESR & Low Resistance Test Meter
Posted on Monday, May 2, 2011   •   Category: Test and Measurement


As electrolytic capacitors age, their internal resistance, also known as "equivalent series resistance" (ESR), gradually increases. This can eventually lead to equipment failure. Using this design, you can measure the ESR of suspect capacitors as well as other small resistances. Basically, the circuit generates a low-voltage 100kHz test signal, which is applied to the capacitor via a pair of probes. An op amp then amplifies the voltage dropped across the capacitor’s series resistance and this can be displayed on a standard multimeter. In more detail, inverter IC1d is configured as a 200kHz oscillator. Its output drives a 4027 J-K flipflop, which divides the oscillator signal in half to ensure an equal mark/space ratio. Two elements of a 4066 quad bilateral switch (IC3c & IC3d) are alternately switched on by the complementary outputs of the J-K flipflop. One switch input (pin 11) is connected to +5V, whereas the other (pin 8) is connected to -5V. The outputs (pins 9 & 10) of these two switches are connected together, with the result being a ±5V 100kHz square wave. Series resistance is included to current-limit the signal before it is applied to the capacitor under test via a pair of test probes. Diodes D1 and D2 limit the signal swing and protect the 4066 outputs in case the capacitor is charged.


RF Control for Home Appliance
Posted on Monday, May 2, 2011   •   Category: Remote Control


This circuit consists of Transmitter and Receiver section. The circuit can be used to control home appliances within a range of 30 meters. In open area, you can expect a range of 100 meters. The circuit comprises HT12 Encoder and Decode IC's. HT12 Encoder is used in the transmitter (remote) circuit where as HT12E is used in receiver circuit. The Encode IC encodes the 4 bits of data and transmit it serially to to RF Transmitter module. These 433Mhz transmitter and receiver modules operate using ASK Modulation.


Light RF Remote Control
Posted on Sunday, May 1, 2011   •   Category: Remote Control


This is another remote control for my RF light switch. Pretty much the same as before but on a smaller PCB. Also ended up putting it in an old Maxim sample box. I found a couple of button nubs in my junk box so decided to go with those. Even so I had to raise the buttons with pieces of rubber. A piece of tape keeps the buttons from falling out when the box is opened and also adds some tolerance for misalignment.


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