Instructables

433 MHz UHF lost model radio beacon

Picture of 433 MHz UHF lost model radio beacon

Here's a simple 433.92 MHz short range radio beacon that may be handy for locating downed R/C planes, lost ballons, model rockets - or perhaps hidden transmitter "fox hunts"!  433.92 MHz is internationally a free band slot, and although only low power transmitters (10-25 mW) are legal, UHF signal punch thru' light vegetation etc is superior to 2.4 GHz microwaves.  

It's based around a cheap (~US$5-10) low power (a few mW)  Keymark/Spirit-On TXC1 data transmitter, fooled into transmitting audio tones generated by a cheap PICAXE-08M microcontroller. Ranges are up to a km line of sight, dropping to  100-200 metres thru' light vegetation and wooden buildings etc.  Compared with flashing lights & beepers, the beauty of a wireless locator relates to all hours convenience & simple direction finding even thru' light vegetation etc.  A cheap "sniffer" receiver ( based around a companion RXB1 Keymark receiver module) is shown at => http://www.picaxe.orcon.net.nz/433rx.htm

NOTE- keep this simple locator beacon approach in perspective! Do not expect it to locate the likes of your $$$$ FPV (First Person View) model plane downed miles from anywhere in deep woods.  For serious locator use, more powerful  transmitters & GPS encoding should be considered. These of course can be costly, have higher battery drain and may be tedious to configure .

UPDATE - early 2012:  Chinese firm Dorji have recently released some cheap (< US$10 a matched TX/RX pair) ASK 433 MHz data modules that significantly improve this beacon! Their transmitter is particularly appealing, as it's power is boosted to a (legal) 25 mW, giving ranges  some 4-5 times greater than the KeyMark/SpiritOn equivalent ! A sensitive UHF scanner can still detect it thru' light vegetation etc to ~500 metres, and LOS (line of sight) several km ! The Dorji receiver, which usefully can also be persuaded as a band monitor, is somewhat more sensitive than the Keymark as well.

Since these Dorji ASK modules have shown themselves clearly superior, more versatile, smaller and far cheaper  they're now recommended instead of the Keymark! As circuitry & layout will need to be slightly changed however (see => www.picaxe.orcon.net.nz/dorjiask.htm  & a Dorji based 433 MHz  "sniffer" receiver =>   www.picaxe.orcon.net.nz/dorji-tonerx.jpg ), the Instructable is presently still Keymark module based.

Update -Nov. 2012 :  A superior Dorji based tape measure antenna Instructable is now available => www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/
 
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manuka (author) 1 year ago
A Dorji ASK module based Instructable, featuring a 3 element Yagi tape measure antenna, is now available => www.instructables.com/id/433-MHz-tape-measure-antenna-suits-UHF-transmitte/
Gizmobot1 year ago
Thanks for the recent update . . . this is an awsome instructable . . .
I am thinking this would work perfect for a "hide and seek" sort of game for my kids - we are working on some map reading and orientation skills - before a big backpacking trip.
Would this be a good fit for a game where I used 6 or 9 of the transmitters as hidden "treasures" (say in a waterproof box or pvc pipe) then gave the kids a map with the locations marked and let them have a receiver where a LED light or group of lights would come on as they got closer???
I have seen some references (including one in the link below) to these being used in "fox hunts" or geocaching - but hadn't seen anything specific so as a relative newbie I thought I maybe should confirm. :-)
Thanks again for all the great information!!
manuka (author)  Gizmobot1 year ago
Gizmobot: Happy to help- combining electronics with the outdoors makes for an appealing activity for high energy youngsters!

Further sleuthing with the Dorji module has revealed a valuable signal strength tap that suits enhanced work- refer attached pix. In conjunction with a 433 MHz tape measure Yagi antenna absolutely remarkable performance has resulted.

I'm still organizing this as a brand new Instructable, but have uploaded pix to =>https://picasaweb.google.com/113235065280579741262/Dorji_DF

Stan
dorji_433_band_rx_CAGC.jpg
manuka (author) 1 year ago
Oct. 2012 updateYes ! Dorji's DRA886RX  receiver module readily converts to general 433 MHz band monitoring. Check the quick "proof of concept" breadboard layout below -diverse circuitry alterations naturally can be made. Refer Dorji ASK module insights => www.picaxe.orconhosting.net.nz/dorjiask.htm

Although of course NOT as sensitive as a dedicated $$($) UHF scanner, such a 433 MHz data module hack is dirt cheap,educational,dead easy to use & is particularly handy for diagnostic checks on all manner of 433 MHz devices. Investigate (by HEARING/SEEING band activity) the likes of wireless door chimes, backyard weather stations, car remotes.garage door openers, wireless data devices,local 433 MHz band interference,pickup antenna and device siting benefits etc etc. HIGHLY RECOMMENDED!
dorji_433_band_rx.jpg
Very cool idea. I saw these modules on Sparkfun the other day and thought they might be used for robot navigation (distance and bearing).
manuka (author) 2 years ago
Happy to help ! Perhaps initially check my crusty old PICAXE resource site http://www.picaxe.orcon.net.nz for ideas. However the best PICAXE resource is at the makers http://www.picaxe.com  This Hellscreiber circuitry is really an engine - it can modulate almost any transmitter. I simply used the 433 MHz one for simplicity. Stan
thanks, again -
great resource & helpful script which allows to create different types of rf sending/receiving devices !
manuka (author) 2 years ago
Marc: Where are you ? Have you referred to the SMT resource page => http://www.picaxe.orconhosting.net.nz/smthell.htmThe PICAXE-08M SMT code is here =>http://www.picaxe.orconhosting.net.nz/VKZLHELL.BAS
please accept my apologies for my late reply-
and, much more important:

thanks so much for posting the links!
will have a look at it asap - (late over here - 4.20 AM)

(did some research meanwhile and found another really helpful example on instructables
http://www.instructables.com/id/Wireless-temperature-sensor/ )

besides:
orcon has plenty of sources too, thanks a lot, again!

Best Regards
Marc
am a total newbee to picaxe (not to mention microcontroller coding)
hence commands such as HIGH, LOW, SLEEP and GOTO are not easy enough to master for me yet :

- would you mind to hint me towards how to code this
or
probably post a link for similar examples ?

apologies for being that helpless - i did my googling
and did not find one example for a newbee-easy-to-understand-
picaxe rf transmitter-receiver example
including code and schematics example yet
(not to mention a "breadboarded" or "circuited" image coming with it)
and was happy to find your instructable!

however: thanks for posting all this!
i would love to build this -
may i ask which code you are refering to ?

http://www.picaxe.orconhosting.net.nz/
- Multi-tone (SMT) Hellschreiber

which -amongst other links- links to ...
http://www.members.westnet.com.au/page3/picaxe-08m_mimi_28mhz_beacon.htm

which links to ...
http://www.members.westnet.com.au/page3/PICAXE-08M_Mini_28Mhz_Beacon_Code_Ver2.txt
sdtacoma3 years ago
This looks awesome. I am interested in building one to track down a balloon. Do you have a list of parts used? I see them here-and-there in the Instructable but a list would be very helpful.
The range of this project will be too small to locate a Balloon that may have landed miles and miles away from you.
manuka (author)  looking4ideas3 years ago
looking4ideas: Splutter- I DID say limited range at the intro ! A simple RDF antenna (such as a "cotanga" Yagi) can give a few hundred metres range thru' light vegetation & a good 500m- 1km line of sight (LOS). Elevating yourself on a low hill, rooftop or even a ladder can allow scanning over a field etc for beaming insights. Many lost models & balloons etc are of course snagged in the tree tops, and may otherwise be invisibly almost above you when searching at ground level!
Yes, the range is not good enough to find it from miles away. I am just hoping that this can narrow down it's direction/location when close to it. Plus it is small and light.

manuka (author) 3 years ago
go_junior8: Bravo on the keen observation! The cap. can go to either pin of the PICAXE, but I'd moved it to it's own output ( "Pin2") on this Instructable for flexibility. This way the LED can be controlled on it's own. On the older layout I had it in parallel with the LED of course at "Pin1". The PICAXE will indeed have to be programmed with something first. For insights see resources such as http://www.picaxe.orcon.net.nz 
manuka (author) 3 years ago
Good point! I'll add a parts list to suit. The key goodie however is the Keymark/SpiritOn 433 MHz TX module.
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