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  1. walid1

    A sleep Timer

    Hi The following circuit is function as a sleep timer: from: http://www.redcircuits.com/Page4.htm I edited it and put the parts values and some other information The writer wrote the following about it: {After turn-on by P1 pushbutton, the LED illuminates for around 25 minutes, but then it...
  2. walid1

    NAND gate

    Hi look at the figure shown below: you noticed that the two nand gates have the same inputs, so they willl have the same outputs the led is always on till all the i/ps are High my question: if the two nand gates have not the same inputs, and the o/p of one of them is high and the other is low...
  3. walid1

    Logic gates question

    Hi everybody If i have 4 inputs (logic 1 or 0) What logic gates must be to light a lamp if only two (any two) of the input is at logic one? THANKS
  4. walid1

    Hearing aid circuit

    Hi for the following circuit if i replace R2 by 10 k and C3 by 10u what would youy expect. someone told me that the circuit operate fine it is a hearing aid thanks
  5. walid1

    The caps surrounding the LM7812 regulator?

    Hi please look at the attached figure below: u can see two caps around the LM7812 I go to datasheets and read about them, After read that I felt I did not reach the result required. can you explain it more fore me Thank you for your cooperation
  6. walid1

    OVER-/UNDER-VOLTAGE PROTECTION CIRCUIT ANALYSIS

    Hi The circuit attached below is OVER-/UNDER-VOLTAGE PROTECTION. I have some questions: 1- R4 & R8 are 1K why not 10K? 2- Why D5? 3- the voltage divider consisting of the resistors R1, VR1 and R2, is to monitor the voltage, i can use the same voltage division with smaller or bigger values...
  7. walid1

    LM308 maximum ratings

    Hi all my friends In the datasheets of  Lm308 attached below (at the end) I cut this part for discussion: and here are the notes: my questions: 1- What is the differential i/p current, and how to ensure that it will not exceed    10mA? 2- Please explain Note 1, I did not understand it...
  8. walid1

    high wattage resistor in batt charger?

    Hi Why, usually using a resistor with little resistance and high-value wattage in  battery chargers circuits? why not connecting the batt directly with the source? thank you
  9. walid1

    transistor as a switch

    Hi can you explain What R8 (1K) exactly do? is it a voltage divider?? thanks
  10. walid1

    very simple PS

    Hi please look at the figure below: if as seen, the X1 secondary voltage is 6V AC, then the rectified DC voltage after the bridge and a cap (1000u/25V) filter is 6* sqrt 2 =8.49 VDC is this true, please comment. thanks
  11. walid1

    IC controlled emergency lamp with charger

    Hi all In the attached file below u can find the circuit diagram of the IC controlled emergency lamp with charger my question is what the purpose of using D5 and D8, what they do in the circuit?? thanks
  12. walid1

    Adjustable precision shunt regulators, TL431

    Hi In its datasheets attached below, and looking to the atteched figure below, we can see that: Vout = (1 + [R1/R2]) * Vref If +V = 12v, R1 =10k, R2=2K What is Vout I cannt understand how to get Vref value please help me to solve this thanks 431-2.pdf
  13. walid1

    transistor saturation

    Suppose that You used a transistor 2N3904, in its datasheet I found that the Po = 625 mW; the power which this transistor can dissipate (in the form of heat) equal to 625 m Watt. Now, if we assume that VCE = 0.4 V at saturation, this transistor can pass to 1.5 ampere as Ic. But in the datasheet...
  14. walid1

    Computer power supply question

    Brothers hurt, the most important stage in the Computer power supply is the input stage
  15. walid1

    Crystal examiner

    Hi often have some friends with their remote control to to repair it. This requires that you have the examiner Cristal to ensure the validity of this piece. In the past, I was immediately replaced them with new, but I know I need to examine the crystal. Searched in the internet and I found this...
  16. walid1

    help in using google

    hi all sometimes i want information about IC It is easy for me to write its number and get the datasheets I want circuits that uses that IC, what to do. can anyone help thanks
  17. walid1

    cordless phone SENAO SN-736

    Hi I need the circuit diagram of SENAO SN-736 thank u very much
  18. walid1

    Help me to understand the MC3359P IC

    Hi Below I attached the datasheets of the MC3359P IC. I have a ruined cordless phone (SENAO SN736) From this phone I’ll get that IC and the related components, and with your help and some modifications, I want to build a FM receiver. Lets go: (1) What the meaning of RSSI written at the...
  19. walid1

    preamp op amp circuit question

    Hi For the circuit shown below I want: to calculate the o/p gain to know what the function of C1 I noticed that there are something strange in it, the feedback is connected to the noninverting i/p and the voltage divider to the inverting i/p thank u in advance
  20. walid1

    a high pass filter question

    Hi when we come to design a high pass filter like that formed between stages Here C is the coupling cap and R is the i/p impedance of the next stage the cutoff freq = 1/(2 pi R C) To make the cutoff freq = say 100 Hz, u can: take C = 10 uF and R = 160 ohm OR take C = 1 uF and R = 1.6 Kohm You...
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