Fullscreen HTML5Med Res (??MB)HTML4

Simple, Cheap 433MHz Locator Transmitter ...perfect ... perfect for use as a • Lost model plane or rocket finder • Stolen bike or even missing pet tracker • Fox hunting • and much more! So you made last month’s 433MHz “sniffer” receiver and now fancy some adventurous tracking? Here’s a versatile PICAXE-08M controlled transmitter, based around Jaycar’s ZW-3100 companion 433.92MHz ASK (Amplitude Shift Keying) module. While relatively short range, this transmitter makes a great model plane or model rocket locator and/or tracking beacon – something we’ve been asked about numerous times. siliconchip.com.au by Stan Swan February ebruary 2011  67 Solar power could even be considered but a model plane or rocket lost in dense vegetation may naturally mean little solar charging occurs. The method of assembly is not critical and could be built on solderless breadboard for trials, then transferred to the tiny PC board as shown here if weight and size is an issue. A homing beacon This Altium Designer diagram is actually much larger than life size. The 433MHz transmitter module is mounted flat to make the smallest package possible – this necessitates removing the four pins on the module and soldering direct to PC pins. Note the pins are offset: there’s a wider gap on the “ant” side. U sing last month’s “sniffer” receiver and simple wire antennas, line-of-sight (LOS) ranges of 1km have been achieved from this simple transmitter, falling to several hundred metres when light vegetation and wooden buildings obscure the propagation path. Better receivers and antennas (perhaps a UHF scanner and Yagi) could significantly extend this range. The transmitter module Jaycar’s “always works” ZW-3100 433MHz transmitter module has long been recommended for simple wireless data links. We’ve used it before for assorted wireless projects and although rated at only a few milliwatts (meaning it’s not going to blister paint on nearby buildings!), this module gives a good account of itself, especially when elevated and feeding a decent antenna. Although they’re essentially a slow (300-10kbps) data transmitter, pulling the module’s data line to the supply voltage via a 10kΩ resistor means capacitively-coupled audio tones can be sent instead. Although more sophisticated and powerful 433.92MHz offerings are now appearing (and are under consideration for a possible future article), these can be very demanding to configure! PICAXE driver The legendary versatility of the PICAXE-08M allows beeps, simple tunes, Morse ID, or even sequential multi-tone (SMT) Hellschreiber to readily modulate the transmitter. 68  Silicon Chip Deep sleep periods can be included as well, greatly extending battery life – perhaps an important issue for a homing beacon. Power supply The transmitter module is normally rated for just a 3V supply, although some data sheets indicate 6V may be used. To remain on the safe side, we’ve supplied it via a 3 x AA (ie ~ 4.5V) PICAXE-switched control line. With such a supply, under 4V will normally be on the TXC1 positive. Use of a 4 x AA holder and a dummy cell allows versatility for use of weary batteries or lower voltage rechargeable cells as well. A ~ 100mAh lithium coin cell may even be suitable but duty cycles will have to be very low to prolong battery life in this case. The circuit shown uses about 10mA but if powered on for (say) just a few seconds every minute the average would drop to under 1mA. Alkaline cells of 2000mAh capacity may thus last hundreds of hours, translating to perhaps months of beacon service – a key benefit when trying to locate a device before batteries run flat. Googling “lost model plane” returns all manner of heartbreaking tales relating to searches for downed radiocontrolled planes. These models may be worth thousands, especially FPV (First Person View) types that carry a video camera aloft. Tall grass, crop fields and trees may so frustrate the hunt that a searcher could be within metres of the model and never find it. Flashing LEDs or alarm sounds may help but these may only be seen at night or heard in quiet locations. However, wireless beacons can be detected at any time, provided the vegetation and terrain is not too dense. Simple radio direction finding (RDF) and triangulation can assist in the hunt. For more professional applications GPS encoding of course may be an option but (aside from cost) the increased battery drain and weight may become an issue. A simple 433MHz “ping” beacon may save the day! While the original intention was for a homing beacon for lost model planes and rockets, there’s nothing to stop you incorporating the transmitter into a host of other devices – a pushbike, for example or perhaps even a car. Sure, you have to get quite close before you’ll start receiving a signal but believe it or not, that’s more often than not the norm (especially for “pushies”, which are often dumped only a few blocks away from where It’s called the “Ugly Albatross” and its claim to fame is the FPV camera mounted on the nose. It’s not the sort of plane you’d be real happy about losing and our 433MHz tracker suits it perfectly. siliconchip.com.au SUITABLE ANTENNA: ~170mm WHIP OR YAGI (TO PC SERIAL PORT) C1 100nF CON2 2^ 22k 5^ 10k The circuit The circuit could hardly be simpler: a PICAXE 08M driving the Jaycar 433MHz transmitter module – and not much else! A 100nF capacitor couples the two together with a 10kΩ “pullup” resistor connecting to the transmitter module’s positive supply. This in turn is driven from the PICAXE 08M, as mentioned above. If you can justify the slight increase siliconchip.com.au 3 IC1 PICAXE-08M 4 8 8 7 0 6 1 5 2 3 4 1 ON 330 ANT 433.92MHz ISM +V TRANSMITTER MODULE DATA (JAYCAR ZW-1300 GND OR SIMILAR) 10k 4.5V  LED* 4 ^ CON 2 PIN NOS REFER TO DB9 PLUG * OPTIONAL -- SEE TEXT ANT DATA But it’s not all about hunting downed model planes and rockets. While outlining the features of the 433MHz sniffer receiver last month, its use for simple “fox hunting” was mentioned. If this month’s transmitting fox feeds a decent antenna and is elevated, then (compared with a simple quarter-wave whip antenna at or near ground level) coverage will be greatly improved. Perhaps the best antenna for this is a “Slim JIM” (J Integrated Matching), akin to the 162MHz type outlined in the June 2009 AIS article, suitably dimensioned for 433MHz. Stick-style “JIMs” have legendary low-angle omnidirectional radiation and particularly suit horizontal applications. At 433MHz a wavelength is only about 70cm and the Slim JIM antenna is then only about half a metre tall. No special assembly techniques are needed and light hookup or bell wire can be used for the construction. Indeed, two lengths of wire stripped from a half-metre or so of ribbon cable are ideal (and very light weight). Part of the allure of fox hunting is tracking down and finding well-hidden or well-camouflaged transmitters. When mounted inside a suitably coloured plastic tube offcut (or even a length of bamboo), the entire setup (including transmitter and batteries) can be hauled up to a tree branch for enhanced coverage as well as enhanced camouflage! Beacons can be distinguished from each other by suitable encoding as well – simple beeps, ring tones or even snatches of tunes are a breeze to generate with a PICAXE. 2 +V GND “Fox hunting” 3^ I/O PINS 1 ANTENNA ~170mm ANTENNA EARTH (IF REQ) 100nF 10k PICAXE 08M 22k + 2 3 5 PROGRAMMING PINS Fig.1: the PICAXE 08M, suitably programmed, not only feeds data to the transmitter module but also provides it with power from its output 4 (pin3). 10k 330 they were stolen!). Maybe a mercury switch could be used to trigger the transmitter – the thief is quite likely to drop the bike where he finished with it, rather than carefully standing it up as you would! 433MHz MODULE LED* LAID FLAT OVER PICAXE * OPTIONAL Fig.2: the tiny PC board layout. It’s deliberately crammed in to make the board as small as possible. ANTENNA (TOTAL LENGTH ~170mm) Fig.3: here’s the protoboard version. Of course, there are many other ways to fit the components and links but this one is logical. The LED and 330Ω resistor are shown as optional but are perhaps more useful in this protoboard version as it is probably the one most used for experimentation. 10k GDVA in current consumption, perhaps also include a LED on the transmitter board (as shown), as this will visually assist in confirming both transmitter sending and duty cycle. If every nanoamp is vital, simply leave out the LED and 330Ω series resistor. The PICAXE 08M won’t care one way or the other. A 22kΩ and 10kΩ resistor make the connection to the serial port on your PC for programming. Construction While such a simple circuit lends ZW-1300 TRANSMITTER MODULE C1 100nF PICAXE08M 22k 4.5V 330 5 3 2 (RS232) A K LED * 10k * OPTIONAL itself to construction on Veroboard, we are not fans of such. We’ve found far too often that beginners, especially, make fundamental mistakes, such as not cutting tracks adequately. We’ll admit to building our first prototype on Verobard but the final project has been built on a purposely-designed PC board. While this adds slightly to the cost, the chances of even a beginner successfully constructing the project are dramatically enhanced. The board is made deliberately tiny, in fact, everything is crammed in to February 2011  69 Spacing ~20mm 332mm 166mm 1/2 3/4 166mm 505mm GAP ~7mm 166mm 1/4 make it so. This is to give the best possible chance of fitting inside a model plane or rocket. Note that the transmitter module is mounted “laid over” 90° so that it lies across several components including the PICAXE-08M. This is to minimise height – again, to help it fit. This will require you bending the pins downwards 90° before soldering it in (note that if space is not a problem for you, it can be mounted in the normal (vertical) position. Programming the PICAXE is almost always undertaken “in situ” so a 3-pin socket is provided to connect to the serial port on your PC. We won’t go into the programming details again as we have done this extensively in the past. If you can’t find the back issues of SILICON CHIP which cover the subject, you’ll find plenty of information on the net (eg, see my site at the end of this article). A simple 3-terminal programming interface can be made from a cutdown DIP8 IC socket – access this via a 3 header pins attached to a normal serial lead. A “DIP3” socket has the advantage that stiff wire will “plug in”. The alternative, a 3-pin header set, will require a suitable connector. Note that once programmed, the programming connection is removed. We’ve made provision for a pair of PC pins for power connection but if these make the PC board too high for your application (in some, every millimetre counts!) then simply wire direct to the board. Similarly, a PC pin can be used for antenna connection. You will note another hole next to the PC pin: this is for “strain relief” on the antenna wire. If used in a model plane or rocket, vibration can be a real problem so the cable threads through these holes before attachment. There’s also another pad alongside the antenna PC pin – this is for the braid (earth) of 75 Ω coax cable if this is required for connection to an external antenna (such as the Slim JIM shown here or the Yagi shown last month). If used, the LED can be mounted on the board or connected via flying leads so that it can poke through the plane or rocket fuselage (and so be seen externally). Choose a superbright LED for best effect (contrary to what you might think, superbright LEDs draw no more current that ordinary LEDs). We’ll leave both the battery holder and the power switch for you and 35mm 50 COAX FEED TO TRANSMITTER Last month we showed how to build a simple 4-element Yagi which could be used for transmitting or receiving. The famous Slim JIM antenna above, with dimensions shown for 433MHz, can also be used for both and has the added advantage of being thin and therefore highly camouflage-able! With the very low power of the transmitter, just about any wire can be used (strands from a rainbow cable would be ideal). To keep it rigid, you could glue the wire to the outside of a piece of 20mm (OD) PVC conduit which, for protection, could be slid inside a length of ~25mm (ID) conduit. By the way, the top and bottom do NOT have to be the nicely rounded shape shown here! 70  Silicon Chip Here’s the “Slim JIM” antenna we made to suit the transmitter, from the dimensions at left. Basically we hot-melt glued two fine wires to the outside of a length of 20mm conduit. Highlighted (red circle) is one of the two connections between antenna wire and 50Ω coax cable; the coax solders through holes in the conduit. Inset are two views showing the method of construction – we used hot melt glue to tack the wires in place and to seal the ends against little intruders! The right-hand photo is the completed antenna fully encased in its outer conduit, ready to connect to the transmitter (it also works fine as a receiving antenna). siliconchip.com.au ‘Simple two tone TX modulator – refer www.picaxe.orcon.net.nz/433fox.htm DISABLEBOD ‘ turns off brown out detection TX: ‘ transmitter routine HIGH 4 ‘ turns on transmitter module HIGH 1 ‘ turns on TX LED SOUND 2,(100,10,0,10,120,10) ‘ 2 tone beeps modulate TX LOW 1 ‘ turns off TX LED LOW 4 ‘ turn off TX SLEEP 2 ‘ sleep ~5 seconds (units 2.3 seconds) GOTO TX ‘ awakens & repeats routine your particular application (it may be simply a matter of twisting two wires together!). Protoboard version OK, we give up! We know there will be many readers who would be interested in building this for experimentation but don’t want to make it permanent nor go to the expense of a PC board. Therefore, we’ve also shown the traditional protoboard wiring as well – the big advantage with this is that both the protoboard AND the components can be re-used (in fact, the PICAXE 08M can be re-programmed again and again). So the choice is yours – permanent on a PC board or temporary on a protoboard. We’d still advise against the Veroboard route, though! Mounting in a rocket or plane There are several difficulties to overcome when mounting the transmitter PC board inside a model plane for tracking. It’s arguably one of the most hostile places to mount any circuitry. Fast-revving engines and vibration, high g-force turns and the inevitable “slightly harder than normal landing” (ie, a crash!) puts stresses on the components which they were never intended to suffer. Model rockets are perhaps worse, with the enormous thrust forces on launching. For this reason, you need to make sure that construction is exemplary – stressing a PC board will very quickly test your soldering ability! The second problem is where to mount it. There’s usually not a great deal of room inside a model plane or rocket so it may need to be shoehorned in. Wherever you place it, ensure that it is adequately secured and if possible shock-protected (many modellers use a thin piece of “foam rubber” under or even right around the PC board). siliconchip.com.au The tail area of the plane is usually the least vibration-prone area – and because planes rarely back into solid objects (like the Earth) it is often the least-damaged area in a prang. We’ve provided two mounting holes near the corners of the board. These are intended for tiny cable ties to attach the board to, well, whatever you can. If you must use screws and nuts, there is a very high chance of shorting the copper tracks so a Nylon or fibre washer should be used under the nut. The third problem is the antenna. Most model planes simply have a long wire antenna. At 170mm long, it’s not huge but once again, you need to find somewhere it can go without fouling any engine components or aircraft controls. Ideally, it should be straight out but if this proves difficult or impossible, don’t worry: snake the antenna around obstacles etc. You shouldn’t notice much degradation in range. Try to keep it away from metal components if possible and if it has to “double back” on itself, perhaps add a few centimetres to the length to compensate. Coding A wide variety of modulating tones and duty cycles can be programmed into the PICAXE, with assorted samples shown at www.picaxe.orcon.net. nz/433fox.htm For initial evaluation the above simple two-tone beacon may suit. Disabling the PICAXE “brown out detect” (BOD) allows microamp-level SLEEP. Without it, significantly higher snoozing currents are drawn, which increases the battery drain. The SLEEP period here is deliberately short to streamline initial setup – extend as need be. I’d be interested in hearing of useful applications of this simple beacon circuitry and will offer to host suitable case studies and pictures at the article resource website listed above. SC Helping to put you in Control New Catalog Out Now FieldLogger An 8 universal analog input 512K datalogger. Can fit USB memory stick or MicroSD for additional memory. USB, Ethernet and RS485 connection. Colour screen can be attached. NOD-001 $949+GST Thermostats These small bimetallic thermostats use ON/OFF control to switch fans or heaters. Widely used to control temperatures in cabinets. Range 0 -60C and can switch 250VAC 10A. HEC-005 $29.95+GST Voltage-Current Calibrator Accurately measures and sources 0100mV, 0-15VDC and 0-24mA signals. Fitted with a large easy to read LCD, rugged case and carry case. NOT-001 $495+GST IP65 Plastic Enclosure. Same size as a jiffy box but more rugged and mounting points for your PCB. Fitted with flanges for easy mounting on a panel or wall ENC-060 $15.95 +GST Arduino Inventors Kit. includes new Arduino Uno, baseplate, and a heap of sensors and components. Manual shows how to build 12 projects ARD-015 $93.50+GST GSM Controller. The RTU5011 is a GSM Remote Control and Alarm Unit. It provides 8 NPN outputs, 8 inputs, 4 Analog Inputs and a RS232 Serial Port. Monitoring and control can be done by SMS messaging. KPR-002 $365.00+GST New Catalog Out Now. Ph: 03 9782 5882 www.oceancontrols.com.au February 2011  71