increase the parallel C 2.7 times or , increase the Tx freq 2.7 times .
range depends on the current thru the (ant) loop ., need to check it .

 

1. increase the parallel C? u mean the C which is parallel with the inductor at the receiving part? but i don't think i can get a 0.027uF capacitor..
2. how to increase the Tx frequency?
3. the VR at the Tx, i only need to turn it until i get 5.6K right? or it is a frequency tuner?

 

u can have a 0.022uF
adjust the VR , here Ra is 1100, Rb is ur VR (@5600), C is 0.01
now freq of 555 is 1.44/(Ra+2Rb)*C

adjust Rb or C as per ur need.

 

why must use 1.44 to calculate? which c is used to calculate the f? the C is the numerator or denominator?

i've try this circuit, since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but the output i get is exactly same as the supplied, nothing to do with RF... why?

 

pls refer to
http://www.uoguelph.ca/~antoon/gadgets/555/555.html

also u need "..since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but.." such type of adjustments .
use any nearest value u get.

 

thanks for the info.. yes.. i have already learned how a 555 timer works.. need some time to try this circuit... thanks ya.. any question i'll ask u again.. thanks

 

another question... what is the output at the receiver? is it the same pulse as the 555 timer?

 

yes it will give u the sq:wave when it receives the tuned freq.

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why must the output of the 555 timer (after the 100R) be connected to the GND (-ve terminal of the battery)? can i connect it to nothing? as an antenna..

 

It's not connected to ground, it's connected to an 'antenna', a loop of wire which surrounds your area as you required.

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I think he's asking if the loop will work without grounding the other end, and I think the answer is, not very well. He could tweak the series resistor (100 ohms) to adjust the sensitivity, once he starts to test it. If it works without the GND, so much the better. He did say he wants less than 10cm range.

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Ron

 

Thanks.. Ron H... so u mean... it is better if i don't ground the other end of the antenna.. right? what about the 100R? can it make the range of the detection between the antenna and the receiver less than 10cm?

 

No I definitely did not say that. I thought I was pretty clear.
It might work not grounded. It has a better chance of working if it's grounded. Try it both ways. If it works when not grounded, use it that way. It will save power.

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Ron

 

The output of the 555 timer is the output of the signal generated by the 555 timer.

Connecting a pull-up or a pull-down resistor with a very low value is IMO a bad idea, because current can be wasted that way.

Why not just add a transistor FM transmitter circuit and connect it's "Signal In" to pin 3?
An FM transmitter is also available from antoons Page. See the url that someone posted above as part of their answer.

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mstechca - seems to me that , it's out of context.

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