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DTMF Phone Decoder
Posted on Sunday, January 30, 2011   •   Category: Phone Circuits

DTMF tone is mainly used in telecommunication technology, such as dialing a phone number, handling various services over the telephone, as a selective choice of radio stations, etc. The individual characters are assigned to different pairs of tones. The described decoder Received characters on the LED display, and stores them in memory, where they can be retrieved later. No matter allows for some sequences of characters on and off properly connected device. In practice, the decoder can be built as in the transmitter and connected to feeder line, the transmitter can then be remotely switched on and off, or you can run such a parameter indicating the traffic reports TA in RDS. The required sequence of tones may be part of the jingle.

Importance of X10 Oscilloscope Probes
Posted on Sunday, January 30, 2011   •   Category: Oscilloscopes

A scope probe is built to minimize ringing by adding resistance. A X1 is better than a piece of co-ax, but a X10 probe is more effective than a X1. A X10 probe has the effect of reducing capacitance by a factor of ten. The trade-off is that is also attenuates the signal by a factor of ten. That is, 1/10 the signal applied to the tip of the probe actually reaches the input of the oscilloscope.

MT8870 DTMF Telephone Dial Tone Decoder
Posted on Sunday, January 30, 2011   •   Category: Phone Circuits

Today, most telephone equipment use a DTMF receiver IC. One common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications circuits. The MT8870 isan 18-pin IC. It is used in telephones and a variety of other applications. When a proper output is not obtained in projects using this IC, engineers or technicians need to test this IC separately. A quick testing of this IC could save a lot of time in research labs and manufacturing industries of communication instruments. Here’s a small and handy tester circuit for the DTMF IC. It can be assembled on a multipurpose PCB with an 18-pin IC base. One can also test the IC on a simple breadboard. For optimum working of telephone equipment, the DTMF receiver must be designed to recognize a valid tone pair greater than 40 ms in duration and to accept successive digit tone-pairs that are greater than 40 ms apart.

56W LM3886 / LM3876 Gainclone
Posted on Sunday, January 30, 2011   •   Category: Amplifiers

It is a 2x56W stereo amp based on National Semiconductor's LM3876T chip (they come in 2 versions T and TF the latter having an insulated case), this type of amp is also known as a gainclone because it is an improved copy of Gaincard amplifier. seriously this amp can outperform most commercial amplifiers/receivers (minus the video upscaling/switching) when built properly ie it has very low THD you will not be disappointed by how good it sounds . When connected to AV equipment such as dvd players this thing gets insanely loud (despite having only 56W per channel), i've have never required more than 25% volume because it hurts my ears NOTE: a even more powerful version using the same circuit with a LM3886 chip can be made giving 68W per channel.

LM386 Amplifiers
Posted on Sunday, January 30, 2011   •   Category: Amplifiers

Many electronic projects require the use of a small audio amplifier. Be it a radio transceiver, a digital voice recorder, or an intercom, they all call for an audio amp that is small, cheap, and has enough power to provide adequate loudness to fill a room, without pretending to serve a disco! About one Watt RMS seems to be a convenient size, and this is also about the highest power that a simple amplifier fed from 12V can put into an 8 Ohm speaker. A very low saturation amplifier may go as high up as 2 Watt, but any higher power requires the use of a higher voltage power supply, lower speaker impedance, a bridge circuit, or a combination of those. During my many years building electronic things I have needed small audio amps many times, and have pretty much standardized on a few IC solutions, first and and foremost the LM386, which is small, cheap, and very easy to use. But it does not produce high quality audio... For many applications, the advantages weigh more than the distortion and noise of this chip, so that I used it anyway. In other cases I used different chips, which perform better but need more complex circuits. Often these chips were no longer available the next time I needed a small amplifier.

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