rf coil

[mvs sarma]

if it is aroud distinguhing between two cellponones ringing--RF has nperhpas less to do--all cdma or gsm technology-- setting a bit inyour phone makking it generate (simulate ringing)-- if it is only rquirement-- perhaps one could change the ring tones by selection and crate two different tones  towards ring distingushing--

even if the request is centered around detecting signal from the air-- i fear one may not be able to use simple technics like filters detectors etc,, pardon me --

sarma

 

[arsal_uet]

hi respected contirbuters.
i got the circuit working today, but not because of the coil that is mentioned in the circuit but rather i took a rf coil from the market of about 10mH same as that is found in our radios. so mak it clear that u use the same as that is used in our radios of about 10mH, because its hard to make a coil the way its described in the specification sheet. I almost spent one and a half week on making it but of no use. now my circuit working and of about range of some a meter or a two.To exaplain to the teacher and my fellow class mates can u plz tel me that how at the pin 2 of the ic 7555 when the cal is incoming.i mean to say what actaully happen at that point. because there are two cirrents coming one from top tp dpen because of the batery 1.5 volts and secondaly the transistor.in other words can u plz exaplin the inner working just at the point pin 2.other i can understand a bit.

Can u tel me how can i measure the frequency that is disturbing the coil just to make an additinal feature to the circuit. and what would be the ic that can be used for this.

 

[audioguru2]

i got the circuit working today
now my circuit working and of about range of some a meter or a two.
Good. ;D


Pin 2 is the 555's Trigger Pin. The 555's datasheet explains how it works. The transistor's collector signal triggers the 555 monostable circuit.



It is very complicated to make a frequency display circuit that operates at the extremely high frequencies used by cell phones. My multimeter displays frequencies up to only 200kHz but my cell phone operates up to 1.8GHz, nearly 10,000 times higher.

Here is a clipped paragraph from the datasheet of a 555:

View attachment 38980

 

[arsal_uet]

another problem.
my teacher has asked me to give him the comlpete design.can anybody help me here now

 

[audioguru2]

another problem.
my teacher has asked me to give him the comlpete design.can anybody help me here now

I already showed a clip from the datasheet of the 555 timer IC that explains how it works.
All that remains is the transistor that amplifies the RF signal and the capacitor that voltage-doubles the supply to a high enough voltage to light the 2V LED.

 

[arsal_uet]

me asking for the calculations of the indutor indectance and the capacitor attach to it

 

[audioguru2]

me asking for the calculations of the indutor indectance and the capacitor attach to it

The inductance and capacitance values are far too high to be resonant at the very high RF frequencies used by cell phones. You don't want resonance anyway because cell phones use a very wide range of RF frequencies.

I think:
The capacitor just blocks DC so the base of the transistor is at the proper voltage.
The inductor is just a folded-up antenna.

 

[arsal_uet]

can u plz tel me what is the function of the capacitor c2 that is attached to the shorted pin 6 and 7 and then to ground.

 

[audioguru2]

can u plz tel me what is the function of the capacitor c2 that is attached to the shorted pin 6 and 7 and then to ground.

The datasheet for the 555 tells you how its monostable works:
When pin 2 is triggered by the transistor driving it to ground, the 555's pin 7 reset transistor
no longer grounds pin 7 so R3 charges C2 until its voltage reaches the threshold voltage of pin 6.

 

[arsal_uet]

thanks to all of the contributers to my project.
me got A++ grade in the project.
but i wold strongly recomend that before doing anything just read the monostable operation of the 7555 ic. all the questions wold be solved bc how this circuit works and how the 7555 and the inciming signals works will be clear.

 

[audioguru2]

Hi Arsal,
You got a pretty good grade. Nice going. ;D
I was glad to help you.