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Posts posted by walid

  1. I'm disagree with you, for beginners like us, it is diffecult to search and facing the huge quantity of information and easier to ask
    Also it make this community very rich
    I think there are  many persons who only read what we write and benefeted from that so don't worry at all

  2. I read in a pdf file what appears in fig.oscillator drift below.
    as you see there is 6 points to take into account to make the osc. stable, I'll
    concentrate on the first one labled (a); the c/L ratio.
    what I want is to explain it numerically for FM 100MHz.


  3. I an not so familiar with PNP type transistor.
    when I see a PNP tran. in any circuit like one that shown below that using a PNP, I immediately think to replace - at least in mind- with NPN.
    If I want to do so I must invert the power supply. is this what must to do or there are many other things?
    Another question about the circuit below:
    I see a hartly osc. before many times and noticed that the tank circuit conected-always- between Vcc and collector and not base and Vcc. What the difference?


  4. Please Audioguru tell me how to calculate the freq. of the NAND schmitt in the moisture content detector the first one gate that work as an oscillator
    you answered me before abot two inverters oscillatoe
    i want like that answer
    thank you very much power 10000000000000000000000000000000

  5. This site is good but not excllent, I see it befor, it provide a surface info.
    I want info enable me to identifiy the TX and Rx sections and isolating them and using them say as a walki-talki, or eabling me to make a hand set of different device see another main one, like this.......
    I hear about some people i mt city doing this, what the amazing thing is that those people are out of electronics field at all, what they do? I don't know. How they learn this!!!!

  6. Thank you very very much audioguru, it is helping me very much.
    (1) Gates come in two series, 40xx series and 74xx series, I read somewhere that the difference is that 74xx series working on 5vdc only where 40xx series can work up to 18vdc. Is it right?
    (2) And also I read that 74xx series are TTL and 74xx series are cmos, I don't sure if this true?
    (3) R2 <<< R1 means R1 >= 10 R2 is it ok?
    Thank you

  7. I need a circuit that composed from a 220 to say 12 volts transformer then I rectify this to DC and then connectes to some transistor citcuit. this transistor citcuit must sense the existing or not of the 220vAC.
    if there is no 220volts the circuit o/p is high and vice versa.
    thank you for your help.

  8. Hi all
    The circuit shown below represent a 12 volt battery charger from "Sam Electronic Circuits" and I have some questions about it:
    (1) I noticed in this circuit and all charger circuits that they omit the smoothing cap after the rectifier, why?
    (2) Q1= BTY79 or similar 6A SCR and Q2= C106D  SCR, they are thyristors not traiacs, thats means they latch the state even if we disconnect their gates. How they can control the charging process in this manar?
    (3) D1= 1N4001 which permit current to fllow to the gate and not from it or I think that. But I see that there is no current may pass from gate, please EXPLAIN?
    (4) The GR1= 50V 6A Bridge Rectifier and the transformer is 4A also the Ammeter is 0 to 5A. What making the designer sure that the batt not demand mor current like 10A, what happen if this occur?
    (5) Is it necessary to connect the EARTH to the -VE terminal of the supply as shown in the schematic, EXPLAIN?
    Thank you.


  9. Hi audioguru
    Thank you very much for your very good answer, especially that part about D1 which helps in discharging the cap C2.
    Now, I use Electronic Workbench EDA software to simulate the circuit shown below as Fig.PU1. I noticed that the readings are dependant on R_load value. At low values of R_load zener OFF and I_z = 0 A.
    I record some of these values as follow:

    R_load I_c2 I_R1 Iz I_load V_load
    10K 106.4 1.466 46.30 1.2 12.05
    5K 105.8 1.457 44.24 2.4 12.05
    1K 105.9 1.456 34.33 12.02 12.02
    0.2K 104.4 1.452 0 46.25 9.25
    0.01K 107.2 1.467 0 47.5 0.475

    Can you please explain why this dependence?
    thank you very much.


  10. Hi Audioguru
    First of all I thank you for your kind answer. you must complete the road with me to make me understand as you hope, so
    (1) The 1.6mA, I think you depend on my calculations to get this number, that is 1.6mA approx = 220Vrms/130.5Kohm, is this true?
    (2) If (1) is true, R2 must connected to GND, where is it?     
    (3) I agree with you that it is a half wave, D2 passing the +ve half to zener, and D1 passing the -ve half to GND, the question is why D1, I think that D2 is sufficient to do the job!
    (4) If I want this circuit to provide me a 12 VDC 50mA, I do the following:
            ->for 12VDC I use a 12V zener
            ->for 50 mA I reduce the Rtot to 220/50m = 4.4K ohm\
            -> calculate C2, R1, R2 as follows:
                  C2 is the same 10nF 400V Ceramic or Polyester Capacitor
                  R2 also the same = 470R 

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