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.

Step 1 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.

Comments

[tzq33tdq]

wow. will this work for a weather station?

[Dr_Acula]

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.

[NXTreme]

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_man]

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

?

[Dr_Acula]

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.

[wee_man]

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?

[Dr_Acula]

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?

[wee_man]

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"

[wee_man]

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

[onegizmo01]

Could You Please Add A Complete Parts List for this project? Thanks

[Dr_Acula]

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.

[Xellers]

The radio transmitter in the last step looks relatively easy to make, could you please post some schematics.

[Dr_Acula]

They already come pre-built for a very low price - see the link in step 4.

[Xellers]

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]

Also, please specify the colors on the resistor in order? THX

[Xellers]

And the value of the SMT capacitor...

[Xellers]

And if the transistor is PNP or NPN.....

[Xellers]

The voltage of the battery as well...

[Xellers]

Please.....

[James Moxham]

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.

[bumsugger]

Nice,clean,well presented Instructable James, i'd use the adjective "awesome," but someone beat me to it!

[GorillazMiko]

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.

[vernors]

looks complicated but very cool