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    design PCB using EAGLE

    Use CAM Processor to produce Postscript Files (.PS) of the layers you need. You can convert this file to any suitable graphics format you need. Personally I convert it to PDF so I don't run into problems
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    What is your favorate programing language?

    C, Assembly & VB whatever is appropriate for the task :)
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    Electronic Stethoscope 2

    It should be ok 'C' indicates commertial range & 'P'/'N' indicate package type (I believe P stands for Plastic & 'N' for ceramic). If you get hold of datasheet these differences will be mentioned.
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    SRAM Substitute : Address lines ??

    You don't need the address/data lines in exact order. Your circuit will function normaly. I generally reversr the D0-D7 lines on a 8051 board because they are easier to route that way ;D
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    problem with a rectifier

    Check your multimeter. If you are measuring DC voltage on AC range some multimeters display double the value (this was true with older analog ones). While measuring AC ripple put a 0.1uF cap in series with probes.
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    What is Diac?

    Okey so next time I should say it's a TRIAC without gate ;D Anyway, I have used BC547 with base removed in a light dimmer project instead of DIAC. The project is still working (Don't know how though ;D).
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    line sensor

    I hope this is what u want - http://www.kmitl.ac.th/~kswichit/LFrobot/LFrobot.htm try goolging with 'line folloer robot' for more such links :)
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    Capacitor to charge a battery?

    Regardless of other things, the energy stored in a capacitor is too less to charge the battery. You shall need capacitance in Kilo or Mega :o Farads to charge the battery ;D
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    frequency down conversion from 134mhz-174mhz to 34mhz- 7omhz

    You need a RF mixer for this. Check out the circuit in tunar of a TV. It is an excellant example of a downconverter. With little modifications you can use it for your frequency range.
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    What is Diac?

    DIAC is a 3 layer device N-P-N (take a transistor cut base lead & you get a cheap DIAC ;D). You can also view it as two zeners connected back to back. There was a topic about DIAC some days ago you can search this forum for details.
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    Digital circuit help

    Check out CD4033 it has internal counter & 7 segment decoder. You can use 74hc244 to interface it with a bus. But the discrete logic makes it cumbursome to mux display lines (you need too many IC's). And eventually cost of all IC's will equal a microcontroller. ;D
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    The backwards transistor

    The common base configuration works because collector can provide same current as emitter without caring for the load voltage. Indeed collector acts as a constant current source. You can not operate emitter this way so at the max you will get an attenuator. In fact you can view a voltage...
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    Simulation in Linux?

    Check http://www.sourceforge.net you may find something there. Off the topic also check http://humorix.org/ quite funny. ;D
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    SAW filters

    SAW filters provide accurate filter characteristics which are not influenced by temperature. Also the tolerance from one filter to another is very small. If RC / RL filter is used in it's place it would be very difficult to tune it (forget about replacing it ;D). Check this out...
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    Interpreting Datasheets

    Check out Practicle Transistor Circuit Design & Analysis By - Willems E. Gerald (PS - I am a looser when it comes to spelling ;D ) If you can lay your hands on it. It is the best book to learn transistor design from. Of cource Basic Electronics by Malvino is also a good book but he...
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    DC Motor Speed Modulation

    There are three ways to control speed of DC motor - 1. Field Voltage control 2. Armature Voltage Control (PWM falls into this category) 3. Armature Current Control Please visit http://www.epanorama.net/links/motorcontrol.html#dc there is a much better explanation than what I can provide ;D
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    Buried wire detector

    You need to measure two variables here - 1. Strength of signal 2. Direction of Signal You can feed a unique high frequency signal to the wire at one end so that the wire acts as antenna. And use a sensitive detector to pick up the signal. You shall need two antennas to check the direction. Same...
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    new design need HELP !!!

    Ante, SCR's gate only serves to turn it on. Only way to turn off the SCR is to interrupt current flowing through it. And this is the requirement
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    + and - input/output question

    You can connect LCD panel to transducer (provided these are not supply lines) if output range of transducer matches input range of LCD. (On many industrial devices this may be 4mA - 20mA). You need some thereshold detector to turn on the relay.
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    Digital circuit help

    Search the term 'Switch Debounce' & you will get hardware schmatic for it. As for the counting task check out http://www.ee.washington.edu/stores/DataSheets/cd4000/74c926.pdf but I fear it would turn out more expensive than PIC. P.S. Check out AVR or 89C2051/89C51 they are cheaper than PIC.
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