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  1. Shahriar

    Small Cap between OpAmp Input Pins?

    Hi In the following picture which belongs to a Tone Control Circuit, Can anybody tell me what that Small Value Cap (10pF) Is for? Between In+ & In- Pins I remind I saw the reason somewhere Once, but todayI looked it up in all my books, But did,'t find that. I guess it is some how...
  2. Shahriar

    3uH Inductor at the output of PowerAmplifier?

    Hi In the following picture which belongs to STK4121 Power Amplifier IC, Can Anybody tell me what that 3uH Inductor at the output is for? In Car Power Amplifiers, there are some big Inductors wounded on a big Core, Are they the same as this inductor? ThanX in advance Shahriar
  3. Shahriar

    Universal Laborator System!

    Hi Imagine you want to build a Laboatory System which has a common Shield cable through all Sets.The system should have the capability of talking persons to each other seperately. I mean in the following System with 4 Sets, Person No.1 wants to talk to No.3 and No.4 Wants to talk to No.2...
  4. Shahriar

    Horn Sound when The mic is close to LoudSpeaker!

    Hi I have built a PreAmplifier and a Power-Amplifier and it works Very good when I coonect my PC output to it. When I connect My Electric Mic to it and Increase the volume, a Sound Like a horn appears On the Loud speaker.This also happen when mic is Close to LoudSpeaker. Let me tell My...
  5. Shahriar

    100Hz TV???

    Hi When I go to market, I see some modern TVs which is written on them: " 100Hz Scan " My question is when the Transmitter sends 50 Pictures per second, then How they show 100 Picture per second? ThanX Shahriar
  6. Shahriar

    when should use FPGA?

    Hi, My question is: when should the project use a microcontroller, or when should it uses FPGA? Can you provide a good example of the project. The project that comes to my mind are:             a.  A pong game using LCD interface and push buttons.             b.  A stepper motor controller...
  7. Shahriar

    Send Data to PC Via USB Port Using an AVR MCU?

    Hi Does anybody know How is it possible to send some data to PC via USB Port Using an AVR MCU. I think this is the problem of so many people. ThanX in advance Shahriar
  8. Shahriar

    A vizz Appears on Telephone line when I connect the serial port!

    Hi I have built a device which shows Caller ID on PC via Serial port. that works properly, but the problem is that when as soon as I connect the serial port to my device a Vizz(bad sound) apears on telephone. the serial port has the same GND with telephone line and other pins of serial port...
  9. Shahriar

    Why the Isolted 130V in Tv give us a shock!

    Hi In a TV, in its Isolated Sectin (Cold Chasis), when You touch 130V line, it gives you a Shock? How electricity close its circuit? This happen seriously with High voltage pins in deflection section too. Can anybody say why? ThanX Shahriar
  10. Shahriar

    The Triac doesn't turn off when I connect it to DC voltage!

    Hi I have a Triac, "BT136" when I connect the T1 and T2 Pins to AC voltage, I can turn it off and On with giving a DC voltage to Gate Pin, but when I try to Turn On and Off a DC load, the triac Doesn't turn Off? it remains On, till I disconnect the power! Shold I trigger the gate with a...
  11. Shahriar

    15A Lead Acide Battery Charger!

    Hi Someone has asked me to build a battery charger. The battry is a 24V / 150Ah from those kinds which is used in big vehicles. I think they Are called Lead acide battery!!! Am i Right? the battery is to be charged with a max Current of 15A! I decided to charge it with a circuit like the one I...
  12. Shahriar

    What is "tunable ferrite"?

    Hi I want to build this Little transmitter. In descriptions,is written: " L1 = 9 turns, .15mm wire on 4.5mm diameter tunable ferrite coil former " 1- What is "tunable ferrite"?  L2=15 turns, .5mm wire, 5mm diameter L3=3.5 turns, .5mm wire, 5mm diameter 2- Can I replace L2 and L3 with...
  13. Shahriar

    Outout of a transformer!

    Hi A university expert has said that: Imagine a transformer connected to a Ac Voltage (between Phase and Nuetral i.e. 100V). it has an output of i.e. 12V ac. If you connect this trasnformer to the same AC Voltage (100V) which this ac voltage is comming from Two Phase which have 100V then the...
  14. Shahriar

    Low drop out voltage regulator with TL431 Problem!

    Hi I want to build a Low Drop out voltage regulator(LDO) I tried the schematic Below but the output Changes when I change the input voltage. I wrote the voltages I measured at Vi=8V. I put that 8.2K and 2.2K to create a voltage devider at the base of NPN tarnsistor because the lowest voltage i...
  15. Shahriar

    a Constant Power consumption design

    Hi I have a SMPS that its output varies from 4V up to 32V. As you know at the output of most SMPS there must be a Load to Dissipate some power. For my SMPS, it should be at least 2-3W Because this SMPS is to be used as a Laboratory Supply, I have to put a load at the output. I can not use a...
  16. Shahriar

    What does Complementary Means?

    Hi In Transistor datasheet there is alays a word “Complementary”. For example TIP42 is TIP41 Complement. What does this mean? ThanX Shahriar
  17. Shahriar

    Design Steps in Big Companies!

    Hi Maybe this topic is not related to this forum; Take it easy, because in this case, MP will move the topic. ;D ;D Today, when I was looking at my Camcorder, I thought to myself How Big Company engineers Build such complicated Devices. when a big company decides to design a new device, i.e. a...
  18. Shahriar

    Variable SMPS + Variable Linear PS!

    Hi I want to add a linear PS to a SMPS to improve regulation and vary the output voltage between 0-30V. The Vi in the schematic comes from SMPS .In worst condition it has 250mV ripple. To reduce power dissipation in trasistor I plan to change Vi when I want to change Vo, But I always have to...
  19. Shahriar

    the voltage drop across an Inductor instead of a Res. for current adjust.

    Hi I want ot add a current limit to my SMPS. at the output, I have an inductor that creates a LC filter to reduce ripple. Can I measure the voltage drop across this inductor instead of putting a low Value resistor? Please do not care about little voltage drop across that inductor because of...
  20. Shahriar

    Tracks Shape in RF PCBs are like two comb!

    Hi Today when I was looking at my TV Antenna mixer PCB, I saw that some of the tracks have been made in a shape like Two Comb. you can see such shapes in PC Motherboard's Tracks too. What I guess is that they want the two tracks have a same condition like Twisted Wires to remove the Common Mode...
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