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Posts posted by mozikluv

  1. hi guys,

    the voice activated switch has certain drawback like when your voice is not of the same pitch when you have recorded it. in case you have a hoarse voice or use a high pitch or shouting, it won't be able to recognize your command. just like one of the features of a cellphone on voice activated dialing.

  2. hi hearmewell,

    nice user name you've got.

    all the problems encountered in building this project has been addressed in this forum. the datasheet you were asking is also here. browse thru all the Q & A here.

    good luck

  3. hi thanhyuse,

    i don't know how far you are into electronics, but base on your question i could probably presume you are a real beginner. if that is the case my friendly advice is to look for circuits not using mosfets as the output stage and using single rail supply.

    but if you insist in building that circuit, pay attention to the following;
    R13 & 16 10ohms should be match (same value when tested)
    R14 & 15 220ohms should also be match
    Q1 & 2 should also be match
    you should a single ground point entry
    Q6, 7, 8 & 9 should be properly heatsinked

    i have build that circuit and it was good, just follow the recommended parts. use high quality electrolytic caps.

    hope this would help you :)

  4. ;)hi,

    since you need a long interval the accuracy of using the 555 is questionable since i believe the 555 was not designed for this although it can still be used. try using a programable timer ic like the CD4536 or the CD4541 w/oscillator. you can program this as long as 36hrs. :)

  5. :)hi there,

    it seems a few members have a problem having this project work. my xperience when i first built this project cost me 2 damage CD4027. the most common problem is the damage CMOS.

    another member was asking if the series/parallel signal diode (IN4148) is presented correctl in the schem. yes, it should be connected as presented in the schem. remember that what the author had in mind when he designed this circuit that it can be used to test transistors in-circuit, so he has to employ such circuit configuration. am not trying to be the spokesman of the author but let me try to explain why this circuit is used in the design:

    looking at the schem you will see that the 2 sets of series IN4148 are connected in series with the D.U.T. via its Collector terminal. it works this way, they allow only a current path thru the DUT as long as the transistor is fully saturated. thus insufficient current would flow thru parallel resistances resulting that 1 or both LED would be dark or unlit.

    i hope this would make things clear.

    in fact i have made revisions to this circuit using only 1 ic (CD4093) a quad 2-input NAND Schmitt Trigger in place of the 555 & 4027, but still using the same basic set up on the testing side, and it work just fine. i could check diodes, SCRs & transistors and it could also show the transistor type.

    also pls remember that the output at pin 14 & 15 are at opposite of its other state. when 14 is high 15 is low which causes both LED to flash alternately. so if only 1 LED lights up continously, no alternate flashing, it means one of the output is not functioning. so what would be your logical conclusion. :)


  6. :)hi bonanz,

    sorry i was not able to complete my reply, one way to solve your -5v swupply source is to use a 10v transfo. this is how you do it,
    1. series 2 resistors
    2. shunt the resistors across the rectified output
    3. from the junction of the 2 resistors, this is where you tap your ground
    4. connect the usual filters
    5. connect your 7805 for +5v and 7905 for -5v

    suggested resistance value is 47K 2w

    hope you can benifit from this :)

  7. :)hi bonanz,

    you said you would be measuring only positive voltages, now what would happen if you accidentally reverse your probe. wont your voltmeter get burned? i believe one of the reson why this device was designed to have a dual supply is bcoz of that. if you reverse the probe your display will have a negative sign.

    since you said you only have a 5v positive supply, try using LM7905 to get a 5v negative supply.

    hope this solves your problem.

  8. :)hi EDY

    am i correct to assume that you are trying to build an electronic ignition system, well here's a few that you can consider;

    1. MJ10008 npn 175w 450v 20A (darlington) TO-204
    2. MJ10023 npn 250w 400v 40A (same) TO-3
    3. MJ10015 npn 250w 400v 50A (same) TO-3 :)

    these are motorola products.

    hope this can help

  9. :)hi everybody,

    i will not try to comment why the author configured U5 that way, but here is a very simple suggestion, try substituting with LM386 for U5, see what happens. if the circuit board had been set use an ic socket, solder wires to it and connect to the appropiate holes on the board.

    LM386 pin configuration:
    1. gain
    2. inverting input
    3. noninverting input
    4. ground
    5. output
    6. Vcc
    7. bypass (if you will use connect a ceramic cap 0.01uf to grnd if not leave it open
    8. gain

    this is the output amp of my electronic stet. ;)

  10. :)hi bonanz,

    would you care to provide me with the full circuit diagram of your project once you have solve this problem. i really would to help you out but am not very good at digitals, but am good in building circuits. :) i have read articles about those problem and what they suggest is to use pi filter.

    hope this can solve your problem.

    pls. email me once the problem is solve, thanx ;)

  11. :)hi there,

    you mentioned you used ceramic caps, try replacing those with mylars or polypropylene caps.

    there are several sources of hum in an amplifier,
    1. poor grounding connection
    2. defective capacitors
    3. inadequate power supply filter
    4. poor ground line lay-out
    5. ground line loop
    6. external input hum

    Quest. 1. on a stand alone, meaning no signal input, do you hear any hum from your amp?
    Quest. 2. does your input ground share the same line with your power line ground?

  12. :)hello aichaila & t_ang4 & Staigen

    Aichaila, the C1 is your ripple filter for your power line

    Staigen, there is nothing wrong with the circuit diagram concerning C3 & R7 & R8. I have a question for you to analyze, from U1 output, where do you think does the signal go, does it go to the non-inverting input or inverting input ::)

    T_ang4, nice observation, what do you think is the main function of the gadget? So what do you enhance? ;)

    What kind of microphones are you using, is it the electet condenser microphone (EM-60 or EM-80)

    Aichaila, now that you have made your project work, where are you gonna use it, just curious ;D As an added idea, you can tinker around with the input of U2, you can experiment with different values for R & C, see what you'll have ::) ::)

  13. :)hi t_ang4,

    Question 1: formula for op amp
    Ans: none due to lack of info like amp gain

    Question 2: funtion of each op amp
    Ans: A1 - microphone preamp
    A2 - acts as buffer amp or isolating amp (isolates the input signal to load)
    A3 - buffer amp or unity gain amp (notice there is no Rf only direct connection)
    A4 - LED driver
    A5 - power amp

    Question 3: R14 - 3.9ohms, what will happen if you increase the value.
    Ans. Would like to give you an answer, but would rather let you experiment and see what happens. As a hint R14 works together with C5 to stabilize the output stage and to prevent oscillation.

    Question 4: whats the LED for
    Ans: since this is a stet used for monitoring heartbeat, the 1st led indicates the thumping of the heart and the 2nd led indicates the thomping of the heart. notice the spelling of the word thump & thomp. got what i mean?

    Question 5: you are hearing noise from your headphone
    Ans: what you hear is probably background noises or rf noise

    re Q5, if it is rf noise your line from the output jack could be very long which can act as antenna or your line from the mike to the board is also very long.

    Am quite interested with the outcome of your project, coz i also have designed an electronic stet but my parts count are low and i use it to detect engine noise.

    happy experiment :D
  14. :)hi there DerFly, you hit it rite, you have current overload on your 350. my suggestion is this, determine first your current need, if its 8A then get the needed parts you need, if its 12 A, then do it, there are plenty of circuits in the web, but if you want some allowance for some experiments then make a 25A transfo at 13.8v. this is usually used in a base transceiver.
    here are some sites you can visit:
    1. http://www.sam.dk3.com
    2. http://www.discovercircuits.com
    3. http://www.geocities.com
    happy hunting! ;)

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