REALLY simple wireless?

I am wondering if it is possible to make a simple, cheap, and reliable circuit/device to send out 1-bit data: i.e. i press a button on transmitter, led on receiver turns on. I am fully aware of the various digital radios including xbees, wixels, and nordic, but I don't want or need the features that $20 will get me. I just need 1-bit transfers, on or off. The range doesn't have to be that far (I was thinking 20ft max would be good) and the link would probably be line of sight, but I don't want to use IR. Would it be possible to do something using an RLC setup to simply turn on and off a frequency? But I want it to be as reliable as possible without sending checksums, etc, and I also would like for it to be micro-independent.

Thanks alot!
baum

Here's a little sketch we put together showing an Arduino generating an 88.1 MHz FM radio signal:

http://ruggedcircuits.com/Arduino/fmradio.pde

The point is to show that yes, you can make a very simple RF transmitter without any extra hardware. Now the other side of this is to build the receiver As you say, an RLC circuit tuned to the frequency of transmission may just get you a strong enough signal at short range to look like a digital high.

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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

A cheap 27MHz R/C rig

27MHz R/C rig

How do these work? LC?

Rugged Circuits: I will try that. Once I build the LC receiver, how can I prevent my local stations from interfering?

baum

You can't, really. Instead of FM you may want to knock the frequency down to the AM range and find an AM radio frequency that is not used by local stations. Unfortunately then you are looking at getting longer and longer antennas.

For FM radio (88 MHz and up) our code is relying on the 8th harmonic of an 8 MHz oscillation from the Arduino -- very inefficient, and you really can't play with different frequencies. But the antenna size is reasonable (85cm). For AM radio you can go down as low as 500 kHz or so. With the 16-bit timer you could get 1600kHz (divide by 10), 1455kHz (divide by 11), 1300kHz (divide by 12), etc. One of these frequencies has got to be free on your radio.

--
Beat707: MIDI drum machine / sequencer / groove-box for Arduino

..but I want it to be microcontroller-independent, preferably just using transistors and passives, etc.

baum

Baum,
Do yourself a favor, spend $5 and learnto use virtualwire

http://www.robotshop.com/433mhz-transmitter-receiver-pair.html
17cm antenna (6.7"), can just be a peice of wirewrap wire.

I know how to. And that is what I will probably do, because it is really easy. But I am asking how a REALLY simple one could work using passives transistors, and diodes.

baum

It is really, really simple.
But either unlicensable, illegal or both.

So, do as CrossRoads suggests.

unlicensable, illegal

over ~50ft maximum?

Also, I wanted it to be microcontroller independent, meaning I could hook up a button to the transmitter and an led to the receiver and have a link, but I could also have to micros hooked up, either would work. Keep in mind I don't need anything complex: I just need to send on/off signals, with maybe a buffer op-amp at the receiving end. Could I use a 555 timer, maybe?

baum

over ~50ft maximum?

Over just about any distance you can measure.

Depends on the country, some low power RF (~ 10 mW) don't have to be licensed.
http://www.talkingelectronics.com/te_interactive_index.html

But those only work with the virtual wire library, I want something micro-free that is legal.

baum

In my country (Brazil), most of the frequencies are prohibited.
2.4GHz (typically used by WiFi) is not, if you do not mind to take down your AP, or of the neighbor, you can use this frequency.

Type approval?
EMC?

Right now, though, I don't care so much about the frequency, I am just wondering how I could design a circuit to transmit wireless signals, from there I could change the frequency. Could I use a 555 timer, maybe?

Could I use a 555 timer,

No, not stable enough and will not work at high enough frequency.

Can you take a hint, this project is a non starter, with things like a 555 timer it's not going to be legal even in the US

So it is impossible to do micro free wireless. Alright.

I suppose I can just use on of the rf link units once they come back in stock on sparkfun...

baum

Sparkfun: don't hold your breath, I have not seen the receivers there since August.
Try the $5 pair, or the next one up.

Want a simple transmitter? Get a "high" voltage, and let it spark to ground - then get a simple AM radio and listen for the burst of interference that comes in. Not really practical tho.

If you can make a circuit oscillate, it can be a transmitter, whether intentional or not.
Being able to reliably tune in that transmitter and pick out a piece of data is the hard part.
One way is to have transmitter is transmitting continuously and your receiver tuned into it, and then detect a difference in the signal and report that as different state.
If you're not transmitting continuously, that makes it harder for the receiver as now it not only has to tune, it has to determine the 2 seperate valid states.
That's the nice part about virtualwire, it takes care of getting enough sent for the receiver to do its job.

Designing RF that works from scratch without tools and the engineering background is very difficult.

Here's a simple thing you can try

Get a "high" voltage, and let it spark to ground - then get a simple AM radio and listen for the burst of interference that comes in. Not really practical tho.

As well as being not practical, spark transmitters as they are called are illegal in every country in the world.