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Everything posted by walid

  1. thank you very much for this valuable information !!!!!!!!!!!!!!!!!!
  2. please I want a datasheets for CL8867B-A it is used in cordless telephone, thanks
  3. 8) Since long time I search about formulas used in winding a new transformer such that determining core area, primary and secondary number of turns and wire diameter etec Please if you Know them tell me. thanks WALID
  4. How can I identify IF transformers like this one: 002 0070 P0N2 this is what written at its outside can. I put these numbers in google for search, the results are nothing. can ay one help me please I want to know everything about it like i/p and o/p impedances, turns ratio, ...etec thanks walid :D
  5. Please where can I Find service manuals of cordless telephoes like GREAT FCC ID: A7PCS8100DS Manufactured in TAIWAN R.O.C. beleive me I need it. thanks, walid.
  6. Please I want anything about Wireless telephones, how they work, block digrams, schematic...anything. I have to understand this subject. thank you all for ay help.
  7. i have many Audio Transformer from my scrap, there is no part no., no spcification or anything to identify it. i want to use them in audio circuits, but i want to made some experiments to make an initial idea about them, i kow they are consista of a primary and secondary coils, the primary has three terminals and the secondary has two. in sammery i want to know its impedance ratio. thanks. note dont tell me that put connect it with say 1v rms (50Hz) and measure the output, i know this i want some thing new. you all very good. walid.
  8. I have many of these coils shown in the figure below, the looks like a resistor and have the same colored circle to identify its value, but i cant know is this value in pico H,nano H, uH .... the upper one in the image is brown black black then silver, i think this is 10 xxH with 20% tolerance the one in the middle is yellow violite black then silver, i think 47 xxH with 20% tolerance the last one is brown red gold gold, i think it is 12/10 = 1.2 xxh with 5% tolerance. Thanks
  9. Hi all of you, her is the circuit from: http://www.zen22142.zen.co.uk/Circuits/Misc/insecrep.html you must know that if i go to any part supplier and ask for 3.25" piezo, they will not understand what i want, i depend on scrap board to get my parts, may i have one piezo somewhere but i can't identify it, so it is better idea to see this great piezo. for audioguru i have many speakers from distorted radio-cassette, tvs and telephones, the only data i know is the dc ohm and power rating like 8 ohm, 0.25W. thank you all.
  10. I want to make one, but i have not a piezo, can i use an ordinary speaker, thanks. note: i never see a 82dB peizo if anybody have a picture to see it.
  11. This circuit from http://www.uoguelph.ca/~antoon/circ/flash2.htm is a led flasher, my question is what is its frequency, write the expression used to calculate it? at what maximum freq it can operate? thanks
  12. can i relace it with a 10 watt ordinary speaker to make a pest repeller. thanks.
  13. If I want to simulate the circuit shown in Fig.FM01 using pspice, and I want to module the mic and putting an ac sig source in its place. what are these values representing a human voice: 1- Peak to peak amplitude 2- Rs - source resistance 3 frequency i think it is between 300 to 3400 Hz i choose 2000Hz Now to simulate antenna, what parameters should i have, thanks. Note: Fig.FM01 from: http://hem.passagen.se/sm0vpo/tx/bug.htm
  14. If I want to simulate the circuit shown in Fig.FM01 using pspice, and I want to module the mic and putting an ac sig source in its place. what are these values representing a human voice: 1- Peak to peak amplitude 2- Rs - source resistance 3 frequency i think it is between 300 to 3400 Hz i choose 2000Hz Now to simulate antenna, what parameters should i have, thanks. Note: Fig.FM01 from: http://hem.passagen.se/sm0vpo/tx/bug.htm
  15. When one uses Pspice software to primarily check his simple design before construction, what points should he take in account before transferring to real life circuit? How much the simulation be far from the real circuit? Thanks.
  16. When someone want to make a design using a BJT as amplifier, he needs to determine the early voltage of that BJT. How one determine it, or are there any standard approximations of it? Thanks.
  17. All of us know that beta of any BJT is not constant value and it is change depending on temperature and biasing conditions...etc. L know three methods to primarily determine its value: 1- data sheets (not always available) 2- measuring it using hfe function of a digital multimeter 3- put the BJT in a simple circuit and measure Ic & Ib then calculate it. Now the question is: Which method of the three can I rely on? Or you may have a different method more effective.
  18. What the difference between: 1- Using one 12VDC power supply connected to RC, and 2- Using two power supplies; +6VDC connected to RC & -6VDC connected to RE, thanks.
  19. if I have to amplify a sig of 10mV peak (20mV P-P) using a voltage divider common emitter configuration. Power supply is 9VDC. What values of RB1 & RB2 should be to maintain these two conditions: 1- conserve (not waste) the battery. 2- No distortion in the o/p sig. Note: please write the expression you use to solve this problem, thanks.
  20. Hi audioguru you confused me, is the transistor operate in common emitter or common base? and, if L = 0.2uH what is the carrier frequency? thanks.
  21. I'm asking the entire world what I learn from this picture... The picture provided her is from: http://www.rf.fcpages.com/Fm-spy.htm If you go to this page you will find only this picture without any reliable comment. You find similar pages in more than 90% of the web. They only told you that they are super men and can do what you can't, they challenge you if you can build this circuit, they know you can't because they didn't provide you with the minimum limit of information you need to build it and how they choose the components. If you lucky you may succeed in making this circuit work in any level, what you gain, what you can tell others, I built this circuit and the only thing I know about is that it is FM transmitter, is it enough? Is this the only thing for which you spent your time? If I design a circuit and want to put it for others to help them understanding something I shall provide them with the secrets of my design, how I make it, how I calculate these values... So I want to complete the missing info by correct and incorrect statements, I want to put what I know or think though some is not true. Here are what I think about this circuit and I welcome any corrections, comments or additional info: (1) MIC circuit: consists of power supply (1.5VDC battery) - R 22k - MIC - Ground - R 100 ohm - C 1uF. The R 100 ohm is not necessary be part of ordinary MIC circuits but I think that he put it to attenuate the level of MIC signal so that not to get a distorted o/p sig of the VCO. Its value is obtained by experiments, but the thing which I don't know is how he discover that he needs to put this 100 ohm resistor, may he has an oscilloscope. R 22K ohm used to limit current feeding MIC, the higher this R the lower current pass, this current is modulated by the voice sig. striking MIC diaphragm, you can calculate this current by dividing 1.5VDC/ R (22K). I'm not sure if we can neglect MIC impedance, but the important question her is: how they decide this current value? And the more important question is that: are there some standards to the peak voltages out of MIC circuits that help the designer by consider them in his design. Another point I want to refer to is that if the 100 ohm resistor is to attenuate the o/p sig. from MIC, he can do this by increasing the 22kohm and reduce the number or elements used! May be this incorrect! C1 (1uF) is for DC blocking, it is her to prevent dc currents from flowing to where it must not, if it does it then alter the transistor bias. This C has a value different from design to design. I see many many FM trans. circuits that uses different values of C1 for the same circuits, and when I ask about this they tell me this is not critical, it affect only the tone of the incoming voice, is it true? The human voice frequency is approximately 300-3400 Hz and a capacitor of 1uF has a reactance of about 530 ohms at 300 Hz and 47 ohms at 3400 Hz. These are the two limits of audio frequencies for communications purposes. These values are considered low enough to use this capacitor here. Of course a higher value can be used. Reactance of C denoted Xc = 1/(2 pi f C), where f is the frequency. (2) Voltage Control Oscillator (VCO) consists of the transistor and related components. VCO is an oscillator that changes its output frequency According to transistor's base voltage. What signals are at this base? There are two signals, the first signal is the dc voltage bias from 1.5v battery through the 39kohm resistor to base, which make this oscillator to oscillate at a constant frequency, say 100MHz, the carrier signal. The second signal is the MIC signal which when applied shift the DC voltage bias up and down result in changing the previous mentioned frequency also up and down, thus Frequency modulate the carrier signal according to voice signal. All this is ok I think, now, this oscillator is basically colpitts oscillator. How I know? From the two 10pF capacitors connected from BATT to collector and from collector to emitter. As mentioned before, if no MIC signal applied to base, this oscillator will o/p a constant frequency calculated as: f = 1/[2 pi sqr(LC)]. L is the inductance of the coil and I can't calculate it due to the existence of the ferrite core. I have an expression to calculate inductance for air coils from: http://www.electronics-tutorials.com/basics/inductance.htm C is the equivalent capacitance of the two 10pF capacitors which are in series => C1. C2/(C1+C2) = 5pF. If we know L we can find the main (carrier) frequency. You may get approximate value of this frequency if you operate the circuit and looking to receiver pointer at FM range. If you get it, you can use the frequency expression above to find L. An alternative approach to make this LC portion of colpitts oscillator is to use air coil, calculate its inductance L using the expressions in http://www.electronics-tutorials.com/basics/inductance.htm . You can wound say 5 to 8 turns of insulated copper wire (from a bad transformer or anything else) on a former like a pen. Record the radius of the former {r} and the length of the coil {len} (not the length of the wire) and number of turns you choose {n}. Then choose your carrier frequency say, 88MHz , and finally calculate the capacitor values. You may change the frequency by changing L value, if you squeeze the coil you have more inductance and if you stretched it you have lower inductance since L is inversely proportional to {len}. It is easy to do so if the two caps are equal, but I see many circuits using different values for these caps. In fact most of FM transmitters using colpitts oscillator uses a trimmer upper cap and a fixed lower cap. The upper cap with the coil makes a tuning circuit that permit only one frequency to pass from it. I don't know if we want to calculate the center main frequency whether or not to take the lower cap into account. Someone may tell me! I leave this portion of discussion about oscillator to an expert. Now I go to rest, but when I return I shall tell you what I know about the feedback 1nF cap, the emitter 100 ohm resistor, the filter 100nF cap and finally the antenna 22pF cap. Goodbye.
  22. Reply to audioguru: First of all welcome, I wait for your reply you are my great teacher… (1) You said: “Your audio cable carries a low level signal and hopefully is electrostatically shielded.” What you mean by shield, is this shield which we find inside any antenna cable or you mean that to put signal cables far enough from power cables, if you mean this we then fall down to the first square…… (2) From the rest of your reply I conclude that making a LPF is not the good choice, so, what to do? Yours, Walid. >:(
  23. Reply to Bjorn: You ask: “I'm not sure what you meant when you say that you take the power from you generator. Are you running two power systems at the same time?” No most of the time we take the power from the local electric company, but when the company cut off feeding electricity then we use a standby generator about 500KVA. At the period before the generator handle the load, there is a huge UPS carry out the load for say 15 to 30 seconds. I said earlier that the hum increases especially in audio sig. When we operate on our generator not from the electric company.
  24. Hi Hany, These sites are very good but long text you must be patient read it carefully ask about what you can’t understand: 1) http://www.opamp-electronics.com/tutorials/ 2) http://www.kpsec.freeuk.com/analogue.htm 3) http://www.faqs.org/docs/electric/AC/AC_3.html Please note that you may go to the main page of each site to look at the table of contents and choose subjects or download all and save them for later reading. You must read all what you find and ask about what you could not understand, be patient this is long text. Walid. 8)
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