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Everything posted by walid

  1. Hi I built a circuit that when a person pass some red led illuminate This signal is connected to a pic to count. The problem is that when that person pass, the led is Intermittent lighting glows irregular and weaken and boosted in a very short time The pic see that several persons How can stabilize it at 5 volts Thank you very much
  2. At the outset extend deep thanks to Mr. AUDIOGURU for his effort and interest and wonderful answers. In truth, I thought the circuit was working in a different way, but now the picture clarified somewhat. Still I have some questions: (1)I am confident that your true 100%, but I can not imagine. Note the following figure: please comment. (2) I know that: to turn on the npn transistor, its collector must be connected to +ve batt (through a resistor) and its emitter to ground, then when applying a voltage to its gate it passing current from C to E. In our Q2 its collector didn't connected to any Vcc, so how to be ON. (3) Are concluded from this talk that it could be removed from the circuit without any difference? thank you guru
  3. Hello, Have a look at the amplifier circuit shown I want to know your views about it..... if u find any mistake in it, do point it..... one stage to be mosfet was the requirement, so i have used the mosfet as voltage amplifier and then connected it to the power amplifier...... Thanx for any help MNA
  4. Hi I make a google search "transformrs core materials " i get many information, the followinf is an example: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19650009347_1965009347.pdf hope it benefeted you
  5. Hi at a certain freq Xl = Xc so the series Z = 0 and the parallel Z = infinity if you still confused, please choose some values to C and L and try calculate Z at different frequencies.
  6. Hi I built this circuit on a test board http://www.redcircuits.com/Page68.htm the sensing leads are simply two thin copper wires i connect these two leads together, this equivalent to a very low resistive solution. when operate the circuit, the red led (D3) is on and the other green and yellow are OFF when trying to adjust the variable resistor R4, it has no effect at all i check the connections many times, they are OK. I understand the three comparators operation and know that the two red leds D1 & D2 are a voltage references as the writer said also i know that the first op amp (IC1A) is function like this: and this: I use a 10.5V power supply I measure pin1 voltage = 9.1V where pin5 = 4.3v i try to make pin1 voltage lower than pin5 but can't please help me in fixing the broblem thanks
  7. Hi guru First, thank you very much A thyristor has 3 terminals; A1, A2 and G. Can you please mark these terminals on the schematic (Q1 & Q2). I think they are as shown in the following fig.thyq1q2-001 In the above Fig, and if my idea is true, this thyristor is triggered when a 0 volt signal is applied to its gate. when a high or a VCC signal is applied, it is turned OFF. please guru correct me. there are two push button, P1 and P2, I think you mean P1 which when we pushing it we triger or RESET the counters to begin counting. pin3 of 4060 o/p is zero for 30 minute, and so the thyristor is conducting. at the end of the 30 minutes, pin3 go HIGH so turn off the thyristor. In fact I try to understand the mechanism of turning this thyristor ON and OFF but can't. I used SWCAD III but still unclear. please guru explain it for me. Before pushing P1, the lower terminal of C3 was float. When pushing P1, this applying a negative pulse to the emitter of Q2 turns it ON which turns on Q1. After 30 minutes, the o/p of pin3 is changed to HIGH this applying a positive pulse to the emitter of Q2 turns it OFF which turns OFF Q1. OK, I can keep this in my mind, but i'm sure that i didn't understand how this be done. I'm waiting hope GURU explain it. the last point: Is C2 (=100n) is a part of the thyristor equivalent circuit. thank you GURU very very much.
  8. Hi Three days and there was no answer or response, this means that what I said is true and the original writer of the article was wrong. I have another question: We know that Pin 3 of 4060 turns from Low to the High after half an hour. This High signal is applied to the emitter of Q2 through C3 The subcircuit composed of Q1 and Q2 and related components is responsible for connecting or disconnecting the operating voltage from the rest of the electronic circuit. Can you please explain the mechanism of how these two transistors do their job. thank you very much.
  9. 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 starts to blink for two minutes, stops blinking for two minutes and blinks for another two just before switching the lamp off, thus signaling that the on-time is ending. If the user want to prolong the reading, he/she can earn another half-hour of light by pushing on P1. Turning-off the lamp at user's ease is obtained by pushing on P2.} I calculate the clock pule duration T = RC/0.455 = (1M*100n)/ 0.455 = 0.22 sec Now the clk o/p (pin 9) is ON - OFF at rate of 0.22 sec And according to the values at the above schematic (the colored one), I think that the LED is illuminate from 0 sec up to 15 minutes, then it blinking for anther 15 minutes before the lamp off. WHO IS TRUE THE WRITER OR I'M? thank you in advance
  10. Hi I answer myself look at the followig figure: At the +ve half of the main AC voltage (311 V peak) the upper zener acts as a diode and the lower zD2 acts as a zener regulating the voltage to 16.7v At the -ve half of the main AC voltage (-311 V peak) the lower zener acts as a diode and the upper zD1 acts as a zener regulating the voltage to -16.7v In my software there is no 16V zener, there is a 15 v zener so I use it to simulate this part of the circuit THANKS TO MY TEATCHER AUDIOGURU WHO LEARN ME 99.9999% of what I know in ELECTRONICS
  11. walid

    NAND gate

    thank you guru but i think if one o/p high =5v the other o/p low = 0 volt so it will sink all the current and the LED OFF what would u say
  12. I asked why ZD1 and ZD2 in this schematic
  13. 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, will the LED ON or OFF? thanks
  14. ok thanks guru in the following schematic: Why ZD1 and ZD2? thanks
  15. hi guru to the following circuit, (1)if i changed it to be a half wave rectifier, is the current still 15 mA as with full wave (2) what the difference of putting a 300 ohm resistor in place of the red line or blue line in the followin circuit. thanks
  16. Hi guru (1) the word "at the moment" is the problem if we agree that the voltage reaches 311 volt 100 times per a second that is every 1/100 sec the voltage value is 311v in the human sense it is every time, every any bit of time.......... (2) in this circuit there is no resistor to limit the capacitor's charging current, why there is no problem? (3)Also related to the above circuit; if i increase C1 to 900nF to get about 60mA, when there is no load, zener eats all this current if it is, for discussion, 1/2 watt it will be burned, so if i don't want to use a 2watt zener, and i want to use a 300 ohm resistor in series with the 1/2 watt zener, would this protect the zener? How much this resistor decrease the current? thank you very much
  17. hi please look at the following circuit, it is a transformerless power supply: this is a 12 volt and can supply a max current = 15 mA I calc this current as: Xc = 1/2 pi f C = 14.47 K ohm I = (220 -12 - 1.4)/Xc = 15 mA the 1.4 volt is the drop voltage on two diodes Now, please tell me What are the disadvantages of this circuit, and why the zener diode is Often burned what if i connect 100 to 300 ohm resistor in series with that diode. the last question: at the ollowing circuit, why using R3 =220 ohm its value did not affect the the current at all guru said before that: "The circuit needs this resistor to limit the current in C1 if the circuit was connected to the mains at the moment it is at its peak of 311V" I did not fully understand the intent, especially, I know that the freq of electricity = 50 that the voltage reaches 311 fifty times per second, how can this be? thank you very much.
  18. 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
  19. Hi guru No, the circuit worked i built it 3 times for me and for some frinds it was very very sensitive to voice it picks a very very low voice at night i put it and hear persons speak with eachother, Believe me. the only change i do, it was by a chance, is that it operate very well with one not new 1.5v battery with this batt u will Surprised great ability to capture votes
  20. Hi sarma What is the 0.9V? Why? Hi guru I read somewhere that the Q1 stage voltage gain = approx. R2/R1, with R2 = 680K Av= 680/3.3 = 206, where at R2=10, Av = 3 only?????? No it is biased through R7 = 100K please explain it more. I enjoy seartching the errors I'm sure it is a hearing aid without a volume control, later I'll attatched it. Finally, you use a very good simulator, can you please tell the its name to try get it.
  21. 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
  22. Hi guru BC547 max allowed collector current is 500mA and not 100mA BC327 is pnp tansistor and not npn 2N4401 is 1000mA but the same power of 625mW here is a table of some suggested transistors, i see all are suitable. thank you guru
  23. hi guru It is very good answer. I read somewhere that op-amps designed to be a comparator has an o/p stage like open collector transistor or a darlington pair. is this true? AND what is the frequency compensation ? No thanks I found it in: http://en.wikipedia.org/wiki/Frequency_compensation thank you guru
  24. Hi For a comparator : What will be the form of the o/p when exactly equal voltages applied on the inputs. Also, what the less difference between the two inputs to turn the o/p of the comparator to another, thank you for your attention
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