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Build a 500 metre radio data link for under $40.

Picture of Build a 500 metre radio data link for under $40.
Have a water tank you want to measure or a dam or a gate? Want to detect a car coming down the drive but don't want to string wires through the garden? This instructable shows how to send data 500 metres with 100% reliability using picaxe microcontroller chips and 315Mhz or 433Mhz radio modules.
 
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Step 1: Schematic

Picture of Schematic
The transmitter and receiver circuits are quite simple and use picaxe chips. These single chip microcontrollers can sense analog voltages, turn things on and off and can transmit data. See instructables http://www.instructables.com/id/Control-real-world-devices-with-your-PC/ and http://www.instructables.com/id/Worldwide-microcontroller-link-for-under-20/ for a description of how to program picaxe chips. With a radio link as well as an interface to a PC it is possible to sense data remotely and transmit it anywhere in the world.

Step 2: Transmitter and antenna

Picture of Transmitter and antenna
The transmitter prototype was built on a piece of prototype board. There are a myriad of low power 10mW RF modules available which work well up to a range of about 30 metres. However, once the power goes up above half a watt the RF tends to get back into the picaxe chip and cause resets and other strange behaviour. The answer is to remove the module's antenna and take the RF away with 3 metres or more of 50ohm coax and build a proper dipole antenna. This also boosts the range considerably.
paul12129 months ago
is it possible to send data received from a accelerometr through picaxe 08M to picaxe 28X1 through RF.
en2oh11 months ago
How do you deal with RCVR noise blocking the SERIN and so, freezing the entire PIC.
It looks like you're using the 08M2 chip. Are you using a timeout!

I'm trying to use a number of xtmr's with PICAXE chips providing unique IDs to a single RCVR PICAXE combination. All I need is one XTMR on at a time. Once the ID has been received, the receiver needs to listen for another XTMR's unique ID

I notice your posts on the PICAXE forum. Never knew you were an FP. My wife is a family doc and I'm an anesthesiologist. Small world! ;)

Thanks
Doug

James Moxham (author)  en2oh11 months ago
Good question! I think the newer picaxes get around a serial hang, but the older ones are already hanging when a serin instruction is run. So it is stuck and won't go any further until it gets the header. There will be noise but it doesn't matter so much as the pic doesn't have any other tasks to do until a packet is received. I did find this a bit of a limitation though, and have moved a lot of my projects over to the propeller chip, which has 8 cores running in parallel, so you can have one core dedicated to serial comms and still have lots of other things going on at the same time. Cheers, James
en2oh James Moxham11 months ago
I'm struggling with size issues. Making "smart" magic effects.
Smaller here is definitely better!
Take care
Doug
tzq33tdq3 years ago
wow. will this work for a weather station?
Yes it probably would. Since I wrote this, other solutions have become available. One of the problems with this design is that it may exceed the legal RF power allowed in your country. Given this is generally limited to 10mW, the other solution is to increase the receiver sensitivity. I've been using this one lately http://www.appcon.com.cn/en/product/APC200A43_pro.html as it has can go to 9600 baud, has a higher Rx sensitivity, has an inbuilt 256 byte buffer, and it seems to be a lot more reliable. If you want to pursue this further please let me know and I'll try to find a supplier.
NXTreme4 years ago
It seems that the link is broken. For anyone wanting to find the eBay store listed I think it is http://stores.ebay.com/e-MadeinCHN. They have a page that is just about their radios, find it here. The radios do seem pretty cheap, thanks for pointing them out Mr. Moxham!
wee_man5 years ago
hi I can't seem to find any of these RF modules in my country are their any special names they go by ? and could i connect this like this

Computer ---Serial port ---> RF trasmitter ----------->RF reciver --->Picaxe

?
The modules are on ebay at http://stores.ebay.com/e-MadeinCHN

But no you can't connect it like you say, because the computer RS232 goes from -12V to +12V, and the module expects 0V to 5V. You need a max232 chip and then an inverter gate eg 74HC04. At the other end though, yes you can go from the RF receiver straight into a picaxe.

The technology has been racing ahead in the last 12 months with more and more RS232 to wireless modules coming out at very good prices. Hope and Yishi are two companies making them for a very good price - probably less than the cost of bare RF modules and a picaxe. See my post from 3rd April below.
Also (sorry for double posting) from what i understand from stuff like this is that its sending machine code 00111011 threw the rf modules couldn't one just build a Am or/Fm trasmitter and connect it up?
If you want very simple commands, then the e-madeinchn people have boards with relays on them. Push one of 4 buttons, and one of 4 relays closes. This could be the easiest to configure and I've got one and it does have a long range. Or hack a radio control car and use the servo to turn things on and off. How many things do you want to turn on and off and how much data do you want to send?
Well what i had in mine was using this concept http://www.instructables.com/id/SOCBOT-the-next-generation-vibrobot/ and some how controlling it from the computer wirelessly. Just to freak out my technology ill mother "hehe"
Ok thats a bummer i wanted a remotly computer controlled vibrabot. I will have a look at these other wireless module thingys but its a hassel getting one product and then paying large shipping to new zealand
onegizmo015 years ago
Could You Please Add A Complete Parts List for this project? Thanks
You would need two picaxes and the radio Tx and Rx as described, plus the components in step 1. Having said that, further experiments over the last year have revealed a whole range of better options for sending data with RF modules from companies such as Hope and Yishi. These are true "serial in = serial out", have ranges up to 3Km for a similar price, and are bi-directional. It depends what you want to do - range, baud rate, one direction or two directions, power source, a few bytes or big files. See http://drvernacula.topcities.com/n8vem.htm for an example. If you only want to send a few bytes through over a short range, picaxes with cheap $2 RF modules is still the cheapest option.
Xellers5 years ago
The radio transmitter in the last step looks relatively easy to make, could you please post some schematics.
They already come pre-built for a very low price - see the link in step 4.
Hmm.... I don't need a receiver, and the transmitter looks like I could make it from supplies that I already have. So can you please post a picture of the underside at least so that I could see how it is wired up? Thank you.
Xellers Xellers5 years ago
Also, please specify the colors on the resistor in order? THX
Xellers Xellers5 years ago
And the value of the SMT capacitor...
Xellers Xellers5 years ago
And if the transistor is PNP or NPN.....
Xellers Xellers5 years ago
The voltage of the battery as well...
Xellers Xellers5 years ago
Please.....
James Moxham (author)  Xellers5 years ago
Just checking you have the supplies. The metal tin is not a battery, it is the actual transmitter sealed in a can. The 'resistor' is actually an inductor. There are no parts on the underside. I don't know the part number of the transistor - they filed it off. If you go to www.ebay.com and search for radio module (two words, no quotes), this module comes up fairly high on the list. It is only $2.50 and so there really isn't much point trying to build one from scratch.
bumsugger6 years ago
Nice,clean,well presented Instructable James, i'd use the adjective "awesome," but someone beat me to it!
Awesome! Looks VERY hard to do, but great job, I like how you labeled the images and stuff. You can just edit the image by clicking where you want the tag to be, and drag, it's easier. Nice job! +1 rating.
vernors6 years ago
looks complicated but very cool
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