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I need assistance on one way transmit

jbelectric777

Nov 29, 2012
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I wanted to know if a 555 will provide enough oscillation to send through an inductor and antenna and reach a receiver 15 feet away to turn on an LED.
 

davenn

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Sep 5, 2009
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probably not
what sort of receiver were you planning to use ?
 

BobK

Jan 5, 2010
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I think you might be able to do this, but the two antennas might be considerably longer then 15 feet!

The problem is that the 555 cannot operate a high enough frequencies and would be in the long wave band (below AM broadcast), which requires a long antenna due to the long wavelengths.

Bob
 

hevans1944

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Jun 21, 2012
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If the receiver is powered, which it would have to be to light an LED, you could construct for the transmitter a low-frequency, low-power, RF oscillator driving a loop antenna at a sub-milliwatt level. A simple regenerative receiver tuned to the transmit frequency could easily detect this signal from 15 feet (or more) away and light the LED. That would be fun to build and play with, especially if you are in a learning mode. But if you just want to get things done, a pair of these 433 MHz transmitter/receiver devices is cheap and simple. They are made for sending digital data streams, but should work just fine as on/off signaling devices without the need for an Arduino. You might want to look at this Google page result too.
 

BobK

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Regarding 433MHz modules. If he lives in the US these are not legal. Okay in Europe.

1.2GHz modules are okay in the US.

Bob
 

hevans1944

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Regarding 433MHz modules. If he lives in the US these are not legal. Okay in Europe.

1.2GHz modules are okay in the US.

Bob
You are quite correct. Here is a nice article by Texas Instruments describing what is allowed in the US for unlicensed purposeful operation at low power levels. It explicitly forbids any purposeful radiation from 399.9 to 410 MHz, and 433 MHz is quite close to that band of frequencies. However, I believe that equipment meeting certain FCC Part 15 requirements could operate legally at 433 MHz in the US. Still, 1.2 GHz modules are also common. See this Google results page.
 

Colin Mitchell

Aug 31, 2014
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The output of the 555 drives a transistor that is configured as an oscillator and it gets a pulsed signal. The output of the transistor can be detected up to 200 metres.
The output of the receiver will be a tone and this is picked-off the speaker to illuminate a LED.
 

hevans1944

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Jun 21, 2012
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The output of the 555 drives a transistor that is configured as an oscillator and it gets a pulsed signal. The output of the transistor can be detected up to 200 metres.
The output of the receiver will be a tone and this is picked-off the speaker to illuminate a LED.
Simple is always better. I forgot that AM/FM "pocket radios" are dirt cheap now. Easy to build a little broadcast band one-transistor transmitter and modulate it with the 555 pulses. The circuits were all over the "hobby magazines" in the 1970s, and earlier than that if you built your own two-transistor transmitter. IIRC both AM and FM were popular.

I don't normally recommend that anyone try to build anything from the Instructables website, but here is a nice little DIY FM transmitter project that mounts to the end of 9 V "transistor radio" battery. It is modulated with an electret microphone, but it would be easy to substitute a 555 oscillator to generate a tone rich in harmonics that would be easy to pick off the speaker in a portable FM radio receiver. I like this particular Instructable because it also has a nice little video showing how to make it, including laying out and etching a tiny circuit board.

And if you want to dig a little deeper, visit Colin Mitchell's interactive website (Google that) for an incredible variety of "stuff" that ranges all over the electronics map. You can even purchase all sorts of electronic kits there, just like on Ebay, from a vendor who speaks English as a native language if that is of any help to you.

Hop
 
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