Problem in getting signal from RF MODULES

laxman3018 · Jan 19, 2014

but i ma not from elctronic background so i cant understand that datasheet....pls tell how to connect....???

laxman3018 · Jan 19, 2014

audioguru said:
No Ron.
The 555 uses a HUGE 100uF timing capacitor so it turns on and off at a few Hz. The buzzer makes the tone.
But the metal detector transistor continuously oscillates and holds the 555 always turned off.

A metal detector is supposed to detect the frequency change when metal gets near the coil. This circuit does not detect a frequency change.

so what shud i do

laxman3018 · Jan 19, 2014

audioguru said:
Does the metal detector work or not work? Please say, "Yes it works" or "No it does not work".
The datasheet for the RF Tx and Rx shows exactly how to connect them.

yes it work i have tested it when any metal comes it start beeping sound...

alec_t · Jan 19, 2014

Whether or not the posted circuit oscillates is critically dependent on the coil inductance, according to LTspice. So it can act as a metal detector if the trimmer is set such that the circuit is on the threshold of oscillation.

laxman3018 · Jan 19, 2014

alec_t said:
Whether or not the posted circuit oscillates is critically dependent on the coil inductance, according to LTspice. So it can act as a metal detector if the trimmer is set such that the circuit is on the threshold of oscillation.

the circuit works fine iwant to conect it with rf module. that i can get signal wireless like led glows on reciever side thats it but how shud i connect it with given circuit

audioguru · Jan 19, 2014

I think the metal simply shorts the terminals on the coil.

Don't you think the coil has more inductance and a higher Q when it has a core made from nearby ferrous material? Then it is MORE likely to oscillate?
Oh, the circuit is a brass detector that reduces its inductance and Q? Then the oscillation stops?

Reloadron · Jan 19, 2014

laxman3018 said:
iF i connect that pin 4 to my TE pin of encoder will it work????

I told you, pin 4 of the 555 is the RST. While pin 4 is held low the 555 will not oscillate. Look at the circuit and understand how it works. So you have a signal in the circuit to pin 4 of the 555 correct? When that signal is high metal is detected and when it is low there is no metal detected. So th signal to pin 4 of the 555 needs to be inverted, use a transistor like a 2N2222 or 2N3904 to drive the HT 12E pin 14.

Now on the HT12E pin 14 is the transmit enable pin. When pin 14 is low the /TE is enabled. Read the data sheet for the HT 12E and understand how it works.

You don't really need the HT 12E for this. You only want to light a single LED as I read it but your choice.

Ron

laxman3018 · Jan 19, 2014

audioguru said:
I think the metal simply shorts the terminals on the coil.

Don't you think the coil has more inductance and a higher Q when it has a core made from nearby ferrous material? Then it is MORE likely to oscillate?
Oh, the circuit is a brass detector that reduces its inductance and Q? Then the oscillation stops?

i dont know all about that becoz..i am not from electronic background....so i cant understand all that things...

laxman3018 · Jan 19, 2014

Reloadron said:
I told you, pin 4 of the 555 is the RST. While pin 4 is held low the 555 will not oscillate. Look at the circuit and understand how it works. So you have a signal in the circuit to pin 4 of the 555 correct? When that signal is high metal is detected and when it is low there is no metal detected. So th signal to pin 4 of the 555 needs to be inverted, use a transistor like a 2N2222 or 2N3904 to drive the HT 12E pin 14.

Now on the HT12E pin 14 is the transmit enable pin. When pin 14 is low the /TE is enabled. Read the data sheet for the HT 12E and understand how it works.

You don't really need the HT 12E for this. You only want to light a single LED as I read it but your choice.

Ron

yes i want only one led to glow when metal detects(wireless)
i have both RF modules and HT12e,d encoder decoder...

MY friend told me about BC547 register and told to connect like this...
Take pin 3 from
metal detector, give to base of transistor with 10k resistor. emitter
is grounded. connect RF trasmitter pin to collector. then collector
is connected to 5v with a 10k resistor.
circuit image is down..
will this work????

Reloadron · Jan 20, 2014

laxman3018 said:
yes i want only one led to glow when metal detects(wireless)
i have both RF modules and HT12e,d encoder decoder...

MY friend told me about BC547 register and told to connect like this...
Take pin 3 from
metal detector, give to base of transistor with 10k resistor. emitter
is grounded. connect RF trasmitter pin to collector. then collector
is connected to 5v with a 10k resistor.
circuit image is down..
will this work????

Yes, that will work.When the base is low the out collector) is high. That is what you want to enable the encoder. You may need to reduce the base resistor but that is what you want.

Ron

laxman3018 · Jan 20, 2014

Reloadron said:
Yes, that will work.When the base is low the out collector) is high. That is what you want to enable the encoder. You may need to reduce the base resistor but that is what you want.

Ron

how much resistor should i use at base???

Reloadron · Jan 20, 2014

I would start with 10K as shown and work down. Actually around 2.2 K or 3.3 K should work fine.

Ron

laxman3018 · Jan 20, 2014

Reloadron said:
I would start with 10K as shown and work down. Actually around 2.2 K or 3.3 K should work fine.

Ron

both resister shud be 2.3 or 3.3k...?????
can u do me a favor plss..can explain in simple word what will happen when i will connect that circuit...how it works???? my metal detector works with 9v battery and encoder is working with 5v micocontroller power....

Reloadron · Jan 20, 2014

audioguru said:
No Ron.
The 555 uses a HUGE 100uF timing capacitor so it turns on and off at a few Hz. The buzzer makes the tone.
But the metal detector transistor continuously oscillates and holds the 555 always turned off.

A metal detector is supposed to detect the frequency change when metal gets near the coil. This circuit does not detect a frequency change.

Just a moment here. I just saw AG's post which I missed earlier. Bad Ron, Bad, Bad Ron!

The 555 uses a HUGE 100uF timing capacitor so it turns on and off at a few Hz.

AG in his typical format is on target. Wish I had looked as close as AG did at the schematic. The schematic, as drawn, shows a 100 uF cap as mentioned and on the 555 pin 3 a Buzzer and not a Speaker. I need to give this much more thought.

You say the circuit works. What exactly does the circuit do when metal is present verse no metal. I am sorry I let myself get lost in this seeing what wasn't there.

Ron

laxman3018 · Jan 20, 2014

when metal present than it start beeping and when not then beeping sound goes offf....

audioguru · Jan 20, 2014

No details are given about the circuit.
I betcha the coil only has only a few turns so its inductance is extremely low. It begins to have some inductance when some metal nearby becomes its core. Then the oscillator oscillates.

Reloadron · Jan 20, 2014

laxman3018 said:
when metal present than it start beeping and when not then beeping sound goes offf....

OK and while that happens what happens at the 555 RST pin? Measure the voltage at the 555 RST pin with and without metal being present.

Ron

4pyros · Jan 21, 2014

its my college project already name is submitted and demo is on 24th and its not working

Due on the 24th that does not give you much time.

laxman3018 · Jan 23, 2014

solved ....i used one more BC547 and 2 10 k resistor to work with it....

Reloadron · Jan 23, 2014

Just under the wire too! Glad it worked out for you.

Ron

Problem in getting signal from RF MODULES

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