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radio frequency circuit design

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Nigel Goodwin said:
bananasiong said:
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.
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.
 
Ron H said:
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.

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?
 
bananasiong said:
Ron H said:
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.

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.
 
bananasiong said:
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..

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.
 
mstechca said:
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.

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

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

haa.. yea.. we are talking about the 555 timer as a signal and transmitter but not only the signal.. am i right, akg?
i've already tried this circuit, and it gives response!! but i still need to troubleshoot to get the right frequency and range.. thanks for ur help..
 
the transmitting frequency is calculated by 1.44/(Ra+2Rb)*C right?
then how about the receiving frequency? is it f = 1/(2*pi*sqr(l*c)) ? by calculating the LC circuit? must these 2 frequencies be the same?
 
bananasiong said:
the transmitting frequency is calculated by 1.44/(Ra+2Rb)*C right?
then how about the receiving frequency? is it f = 1/(2*pi*sqr(l*c)) ? by calculating the LC circuit? must these 2 frequencies be the same?
Because of component tolerances, you will need to adjust either the transmitter or the receiver.
 
Ron H said:
Because of component tolerances, you will need to adjust either the transmitter or the receiver.

akg said:
Yes..go on..

thanks ya... can i know.. if i construct the circuit like what mstechca said.. can it be done? i mean from the transmitter circuit. can i use the same value of LC as in the receiver part so that i get the accurate tx and rx frequency? i just want to know what is going on.. thanks!!
 

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i've tried this circuit, and i found out some problems, hope that they can be solved, thanks!

1. can i transmit the signal in 10Hz? i mean, for the tx, R1=1K, VR2=2.5K (use 10K VR), C1=22uF
for the rx, L=100mH and C=2200uF.

2. can i get the signal in that low frequency?

3. what's the output of the op-amp if there is no signal? is it high?

4. and what's the output of it if it receives signal? is it pulses?

thanks for sharing.. :D
 
thanks ya... can i know.. if i construct the circuit like what mstechca said.. can it be done? i mean from the transmitter circuit. can i use the same value of LC as in the receiver part so that i get the accurate tx and rx frequency? i just want to know what is going on.. thanks!!

You know, Nigel is 100% right here with respect to a gigantic number of FM transmitter schematics out there.


, don't pay any attention to what he says!.
any attention? :lol:
If my answers can generate some success, why not?

But anyways, that LC circuit I designed is intended to prevent newbies from creating shorts (unless of course the antenna is connected to +ve).

The LC network alone without the coupling capacitor, and without the antenna is the LC network used in EVERY radio, unless it has a crystal.

the LC network primarily determines the frequency of the signal. There may be other components in a transmitter that could affect the frequency as well.

As for accuracy, your best bet is to use two trim capacitors for C, one being a small range (for fine tuning), and one being a larger range (for coarse tuning, like adjusting a few dozen megahertz at a time)
 
bananasiong said:
i've tried this circuit, and i found out some problems, hope that they can be solved, thanks!

1. can i transmit the signal in 10Hz? i mean, for the tx, R1=1K, VR2=2.5K (use 10K VR), C1=22uF
for the rx, L=100mH and C=2200uF.

2. can i get the signal in that low frequency?

3. what's the output of the op-amp if there is no signal? is it high?

4. and what's the output of it if it receives signal? is it pulses?

thanks for sharing.. :D
u can use low feq , but higher the freq the transmission efficiency and also the voltage induced in the receiver coil will increase.the normal o/p of the ckt is low, when receiving signal , it will give that freq as the o/p
 
mstechca said:
, don't pay any attention to what he says!.
any attention? :lol:
If my answers can generate some success, why not?

Because you were posting complete rubbish, with no relevence to the posted circuit - and with (obviously) not the faintest idea of how it was supposed to work! (as with most of your posts?).
 
akg said:
u can use low feq , but higher the freq the transmission efficiency and also the voltage induced in the receiver coil will increase.the normal o/p of the ckt is low, when receiving signal , it will give that freq as the o/p

but i get a high from the rx output. i tried to connect a LED from the output of pin 1 and ground level but it shows high without the tx.

can i know which part is the antenna for the rx?

if i use high frequeny, i can't see the LED blinking, i think i will use low frequency :D .
 
mstechca said:
The LC network alone without the coupling capacitor, and without the antenna is the LC network used in EVERY radio, unless it has a crystal.

the LC network primarily determines the frequency of the signal.
A parallel tuned circuit is a very high impedance at its tuned frequency. The output impedance of a 555 is a very low impedance and shorts the tuned circuit at the tuned frequency.

Quote audioguru: Posted: Sun Mar 12, 2006 10:59 pm
"A tank circuit is a high impedance parallel resonant circuit. It should be driven from the very high impedance of the collector of a transistor, not the very low impedance output of a 555 where it won't do anything.
_________________
Uncle $crooge"
 
can anyone help me?

i've tried this circuit, and i connected a LED to the pin 1 of the op-amp and ground to the cathode of the LED. when there is no signal, the LED is high.
 
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