audioguru2
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A coil and a capacitor makes a bandpass filter. They can be series or in parallelarsal_uet said:
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Don't know if you have any particular circuit in mind but here is a link where you should start your reading to get "some" understanding in resonant circuits, there might show up better places if you search google.
http://www.ibiblio.org/obp/electricCircuits/AC/AC_6.html
Oscillators is a huge subject, think you should do some studying by your own before you go further.
http://www.ibiblio.org/obp/electricCircuits/AC/AC_6.html
Oscillators is a huge subject, think you should do some studying by your own before you go further.
audioguru2
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Assuming that your cell phone operates only on a frequency between 800MHz and 900MHz (mine operates on many more frequencies), the tuning of the bandpass filter will be very wide.
Don't you think the circuit would pick up every RF signal between 800MHz to 900MHz that is around?
Don't you think the circuit would pick up every RF signal between 800MHz to 900MHz that is around?
Rl= load resistance.
To build a band pass filter 800-900Mhz is not an easy task I would say that some RF experience is needed.
MP it's a good calculator but as you probably know both C and L involved in a band pass filter like this aren't what the average hobbyist usually deal with, I'm not an Rf expert but to get a proper band pass filter for that frequency sure some experience
To build a band pass filter 800-900Mhz is not an easy task I would say that some RF experience is needed.
MP it's a good calculator but as you probably know both C and L involved in a band pass filter like this aren't what the average hobbyist usually deal with, I'm not an Rf expert but to get a proper band pass filter for that frequency sure some experience
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SM2,
The second part of my post was directed at members who stumbled into this thread by the subject line, "Bandpass Filter"
BTW: I think arsal is going in the right direction to learning all about filters, what he can do and what he cannot do.
MP
The second part of my post was directed at members who stumbled into this thread by the subject line, "Bandpass Filter"
BTW: I think arsal is going in the right direction to learning all about filters, what he can do and what he cannot do.
MP
audioguru2
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Why use a bandpass filter that will probably be at the wrong frequency?
According to Red's Cell Detector project, when a cell phone is about to ring it transmits a very strong signal to the cell headquarters to tell them it is ready to receive a call. The detector circuit has just a simple coil at its input which detects the transmission no matter which frequency the cell phone is using.
Arsal said he built a detector circuit that did not work. He also posted questions about a Hitachi ordinary 555 but the detector project must use a Cmos 555 because its battery is only 1.5V. Either he should use a Cmos 555 or he should use a 6V battery in that project, then it should work.
If Arsal stayed in the same thread then his ringing cell phone detector project would be working now.
According to Red's Cell Detector project, when a cell phone is about to ring it transmits a very strong signal to the cell headquarters to tell them it is ready to receive a call. The detector circuit has just a simple coil at its input which detects the transmission no matter which frequency the cell phone is using.
Arsal said he built a detector circuit that did not work. He also posted questions about a Hitachi ordinary 555 but the detector project must use a Cmos 555 because its battery is only 1.5V. Either he should use a Cmos 555 or he should use a 6V battery in that project, then it should work.
If Arsal stayed in the same thread then his ringing cell phone detector project would be working now.
MP I agree, it's a good way to learn how component values change with frequency and bandwidth 
I'm sorry arsal_uet but audioguru is right about the filter, strong nearby signals from other cellular phones or base stations would probably be detected by your circuit. if the frequency would be fixed a narrowband filter could have been a possible solution but then we run into another problem and that is to design and create the filter which need instrumentation that is far beyond what most hobbie electronics can afford.
I do encourage you to continue the project even though it seems to be a real hard thing to solve, don't give up there might be someone lurking around with exactley the right soulution for you, don't forget that you always learn something
I'm sorry arsal_uet but audioguru is right about the filter, strong nearby signals from other cellular phones or base stations would probably be detected by your circuit. if the frequency would be fixed a narrowband filter could have been a possible solution but then we run into another problem and that is to design and create the filter which need instrumentation that is far beyond what most hobbie electronics can afford.
I do encourage you to continue the project even though it seems to be a real hard thing to solve, don't give up there might be someone lurking around with exactley the right soulution for you, don't forget that you always learn something
Sorry I haven't read the other thread arsal_uet wrote.
Audiguru if that's the case a detector is a simple solution but keep in mind that it will also detect every time the cell phone talk with the base don't you think? ;D
MODERATOR EDIT: I have now merged the topics into one 5-3-2006
Audiguru if that's the case a detector is a simple solution but keep in mind that it will also detect every time the cell phone talk with the base don't you think? ;D
MODERATOR EDIT: I have now merged the topics into one 5-3-2006
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audioguru2
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It gets more complicated. The detector must discriminate between two cell phones ringing simultaneousy. This is what Arsal wrote:
"assign me to make a circuit that detects the incoming call, but the problem is he has made a condition if two mobile in the reach are being called simultaneously then that device or the circuit should tell that either they are being called from the same bandwith or the differnt ones, that is are the being called by using the same mobile network or the different.
i have seen the circuit here which just tells us the incoming call from any network any i think, but me want ur help how to make it for atleast two networks and how to make the ciruit sensitive to two seperate networks. and also how to show either using some leds
i want to actuallly catch the incoming call signal for a device to tell me about the incoming call before the mobile rings-
you all might have observed that when u place ur cellphone near ur audia tape or the television or even the mic, a second or so before the call actually appers on the cellphone, ur heard a beep like tic tic from ur audio devices. on the same basis i want to make a circuit that just indicate me by a just light emitting led or thing like this to tel me that a call is comming.
the ciruit whose figure is pasted above, its not working.
HA17555"
"assign me to make a circuit that detects the incoming call, but the problem is he has made a condition if two mobile in the reach are being called simultaneously then that device or the circuit should tell that either they are being called from the same bandwith or the differnt ones, that is are the being called by using the same mobile network or the different.
i have seen the circuit here which just tells us the incoming call from any network any i think, but me want ur help how to make it for atleast two networks and how to make the ciruit sensitive to two seperate networks. and also how to show either using some leds
i want to actuallly catch the incoming call signal for a device to tell me about the incoming call before the mobile rings-
you all might have observed that when u place ur cellphone near ur audia tape or the television or even the mic, a second or so before the call actually appers on the cellphone, ur heard a beep like tic tic from ur audio devices. on the same basis i want to make a circuit that just indicate me by a just light emitting led or thing like this to tel me that a call is comming.
the ciruit whose figure is pasted above, its not working.
HA17555"
Well that is a hard to tackle circuit I would say, to detect rf is one thing but discriminate between two cell phones make things a lot more difficult.
As I understand (and what audioguru said) every cell phone has its own ID and when the base is calling one of the cell phones it answer, here I am go ahead!
It means that to detect that a incoming call is directed to one of your cell phones you got to have a receiver with same ID otherwise the receiver/detector doesn't know which of them the base is calling.
As I understand (and what audioguru said) every cell phone has its own ID and when the base is calling one of the cell phones it answer, here I am go ahead!
It means that to detect that a incoming call is directed to one of your cell phones you got to have a receiver with same ID otherwise the receiver/detector doesn't know which of them the base is calling.
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audioguru2
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Simple, isn't it? Make your own cell phone receivers.
The professor further confuses things by saying it can be done with RF oscillators.
The professor further confuses things by saying it can be done with RF oscillators.
in the ciruit suggested to me by someone here;in that circuit the 7555 has one pin empty. i grounded that pin and now the result is that there is a but high chnge in amplitude across the inductor but that is only about few millivolts and they are not being amplified by the transistor, so tel me how to mak the currnet in crease to mak the led turn on.thanks for ur suggestions all u guys.
audioguru2
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Hi Arsal,
Is this the circuit that you made? http://www.electronics-lab.com/projects/misc/010/index.html
Did you use a Cmos 555 IC like it says?
Did you make the coil like it says?
Did you connect the pins of the transistor the correct way?
Did you use a fresh 1.5V battery? It might work better with a 3V battery.
Pin 5 of a 555 IC is its control voltage. Sometimes it has a filter capacitor to ground. If pin 5 is grounded then the 555 IC won't work.
Measure the voltage at pin 2. It should be higher than 1.0V at rest. Then it should drop to close to 0V when the cell phone transmits that it is ready to receive a call. Then pin 2 should go higher than 1.0V again when the cell phone is no longer transmitting and the LED should blink one time.
View attachment 38949
Is this the circuit that you made? http://www.electronics-lab.com/projects/misc/010/index.html
Did you use a Cmos 555 IC like it says?
Did you make the coil like it says?
Did you connect the pins of the transistor the correct way?
Did you use a fresh 1.5V battery? It might work better with a 3V battery.
Pin 5 of a 555 IC is its control voltage. Sometimes it has a filter capacitor to ground. If pin 5 is grounded then the 555 IC won't work.
Measure the voltage at pin 2. It should be higher than 1.0V at rest. Then it should drop to close to 0V when the cell phone transmits that it is ready to receive a call. Then pin 2 should go higher than 1.0V again when the cell phone is no longer transmitting and the LED should blink one time.
View attachment 38949
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