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A Rudder Indicator For Power Boats, Pt.2 By NICHOLAS VINEN Last month we introduced our Rudder Position Indicator, which uses a 433MHz wireless link to show the direction a power boat’s rudder is pointing. This month we provide detailed instructions for building and testing both units as well as mounting the sensor unit in the boat. A S EXPLAINED last month, the Rudder Position Indicator comprises two units. The sensor unit monitors the rudder and transmits changes in its orientation over a 433MHz wireless link. The display unit picks up these communications and illuminates its LEDs in response. While the two circuits are different, they are both based on ATTiny861 microcontrollers so there are many similarities in layout. Hence the procedures for building the two lower (control) boards, which each have a micro, are essentially the same. You can either build them in parallel or you can build one and then go 76  Silicon Chip back over the following instructions to assemble the other. Control board assemblies The sensor unit control board is coded 20107111 and the display unit control board is coded 20107113. Both boards are 98.5 x 68mm with corner cut-outs; see the overlay diagrams of Fig.7 and Fig.8, respectively. First inspect the copper sides for any defects such as hairline cracks or under-etched areas; repair if necessary. If your boards lack corner cut-outs, use a hacksaw and file to shape them using the thin copper tracks as a guide. Proceed by installing the three wire links which run along the bottom of each board, using 0.7mm diameter tinned copper wire. Run the links close to the board and as straight as possible since they pass near component leads. Next fit all the resistors, checking each value with a digital multimeter before installing it (the colour codes can be hard to read). Remember that you may need to change the value of the 390Ω resistor depending on the intended supply voltage/battery type. Note that, for the display unit, this resistor should be installed slightly offset, as shown in the photo on page 78, to leave enough room for the pushbutton switch to be fitted later. siliconchip.com.au siliconchip.com.au Rudder Position Indicator Sensor Upper Board © 2011 S3 CON6 SC S4 21170102 20107112 S5 S2 S6 S1 S7 CON5 Rudder Position Indicator Sensor Lower Board VR1 5k ANTENNA TP1 2V 433MHz 120107111 1170102 100nF 100nF 12k 1.5k IC1 ATTiny861 100nF 500mA FAST 16V 100 1.5k 82k Q1 + LM2936Z-3.0 100F © 2011 100nF 12V DC TIP+ 1 CON2 SC 1.5k 12V DC 5819 CON1 4xAAA BATTERY HOLDER D1 ZD1 390 Tx MODULE F1 That done, install the diodes. Both boards use a 1N5819 Schottky diode (black plastic body) and a 16V zener diode (large glass body). Make sure they are orientated as shown on the overlay diagram, ie, with the stripes towards the bottom of the board. For the display unit, also fit the small 1N4148 diode with its stripe to the left and the 100µH axial inductor which looks a bit like a fat resistor. Bend its leads close to the body to fit the pads; its orientation is irrelevant. Next, solder in the IC sockets, ensuring that the notches are orientated as shown on the overlay diagrams. There is one 20-pin socket for the sensor unit and 20-pin and 16-pin sockets for the display unit. You must use a regular 16-pin “dual wipe” socket for the 74LS145 IC, since the more expensive type has exposed pins that could short to the adjacent wire links. Now install the transistors. There are two on the sensor unit board and three on the display unit board and there are several different types, so check the markings carefully before soldering each in place. Crank the leads out using small pliers so that they fit into the holes provided, with the flat faces orientated as shown. Fit the regulators next; they look similar to the transistors. There is one 3V (or 3.3V) regulator for each board plus a 5V regulator on the display unit; don’t get them mixed up. Use the same technique as for the transistors. Follow with the small trimpot, one on each board, then the MKT capacitors, which are all the same value (100nF). Note that the 100nF capacitor at bottom left of the display control board (Fig.8) must be mounted on its side (see photo) to leave room for the power connector. The fuse-clips go in next. Push them right down onto the PCB before soldering the pins and take care that the small retention tabs face towards the outside or you won’t be able to fit the fuses properly. Then mount the pin headers, including the 12-pin female header at the bottom of each board (CON3/CON8), a 4-pin female header on the sensor board for the transmitter module (not labelled) and a 4-pin male header on each board (JP1/JP2). If you don’t have 12-way female headers, use side-cutters to snip a longer header at its 13th pin, then remove that pin. You can cut the 4-pin header from the same length. BC547 Q2 OPEN FOR 12V 6V 4.8V LED1 BC327 CON3 Fig.7: follow these parts layout diagrams to build the two boards for the sensor unit. Note that the reed switches (S1-S4) should be mounted 9-10mm proud of the PCB. The photo below shows the assembled lower (control) board. August 2011  77 CON12 Rudder Position Indicator Display Upper Board 20107114 SC LED1 LED14 LEDs 1-13 & 32: RED LEDs 14-18 & 33: YELLOW LEDs 19-31 & 34: GREEN LED19 LED28 LED2 LED29 LED3 LED22 IC2 ATTiny861 100nF 100nF + 100F + IC3 74LS145 100F 20107113 CON8 1.5k 12k 100 100 47F + BC547 82k 1.5k 2.2k BC337 LM2936Z-3.0 100nF D3 4148 100H 12V DC JP2 1k 4 x AAA BATTERY HOLDER ZD2 5819 500mA FAST BLOW F2 16V SC 390 © 2011 TP2 2V D2 CON7 31170102 VR2 5k ANTENNA CON10 Rudder Position Indicator Display Lower Board CON9 MODULE ON/OFF BATTERY LOW ....... HIGH LED32 LED34 FLASH: TRANSMITTER 100nF CON11 LED31 LED27 LED23 LED18 LED30 12k LED13 LED9 LED26 433MHz Rx LED5 LED12 4.8V 6V LED8 LED4 100 1.5k © 2011 REG3 78L05 BC327 Fig.8: the parts layout diagrams for the display unit. Take care to ensure that the LEDs are all installed correctly – LEDs 1-31 all go in with the green dot on their body (indicating the cathode) at lower left, while LEDs 32-34 have the green dot at top left. Below is the fully-assembled lower (control) board. 78  Silicon Chip Next, install two PCB pins on each board, one for the antenna where indicated and one test point (TP1/TP2). If you want a terminal block on either module for external power (or trickle charging the batteries), fit it now. The sensor unit control board also accepts an optional DC socket which can go in now. The 4-AAA battery holder on each board goes in next. Push its leads through the corresponding pads and then secure it using two M2 screws inserted from inside the holder and fixed to the underside of the PCB using M2 nuts. Then solder and trim the leads. If you can only get M2 screws longer than 6mm you can cut them to size with a hacksaw or strong side-cutters but the end will need some filing before the nuts will thread. Now fit the electrolytic capacitors. There is one 100µF capacitor for the sensor unit and two for the display unit, as well as one 47µF type for the latter. In each case, the longer lead goes through the hole marked “+” on the overlay diagram. Push them right down onto the PCB before soldering. For the display unit, cut two 50mm lengths of light-duty hookup wire, strip and tin the ends and solder them to the CON9 pad at upper-left. Modifying the transmitter There isn’t room to mount the 433MHz transmitter module vertically, using the attached right-angle pins. So they are removed and straight pins are installed instead which then plug into the 4-pin female header, so the transmitter module is parallel to the main PCB. The socket allows it to be unplugged to access the micro below. Start by clamping one of the pins in an alligator clip stand or small vise, with the underside of the pin accessible. Then, using a fine-tipped soldering iron, very carefully heat that pad while gently lifting the module so that when the solder melts, the pin is removed. Repeat for the other three. This must be done carefully as there are other pads and components very close to these and you don’t want to accidentally create a short circuit with a blob of solder while removing the pins. When finished, clamp the module in a stand and use a solder sucker or vacuum de-soldering tool to clear the four holes. Now temporarily install IC1 in its socket. Take the transmitter module siliconchip.com.au with the main IC at the top and push a straightened length of 0.7mm-dia­ meter tinned copper wire through one of the newly-cleared holes. Lower the module down so that the wire goes into the appropriate hole on the 4-pin female header and push the wire down fully into place. Now slide the transmitter module down so it’s just above IC1, solder the wire in place and trim it. Repeat this process for the other three pins. If you have trouble visualising how this works, refer to the photograph below Fig.7 to see the final result. When finished, remove the transmitter module and IC1. The radio receiver module can simply be soldered into place on the display unit control board. Locate its antenna input (the pins are labelled on its PCB) and ensure that this pin is soldered to the pad closest to the antenna pad towards the top of the control board. Check that the receiver module is vertical and as close to the main board as possible before soldering all its pins. LED board The next job is to solder the SMD LEDs for the display unit, which go onto the board coded 20107114 (Fig.8). Check it for defects first and make the corner cut-outs, if necessary. While the LEDs are quite small, they are not hard to solder. The hardest part is getting them all properly centred for a neat appearance. The specified LEDs are 3.2 x 1.6mm (1206/3216 size) but the pads are also large enough for 3.2 x 2.4mm (1210/3224 size) LEDs, which may be available with higher power/brightness ratings. Place the PCB down flat on a workbench, copper-side up and install the yellow LEDs first. There are six; five arranged vertically in the middle B A C Soldering the SMD LEDs Install the LEDs one at a time, using the following steps: STEP 1: melt some solder onto one of the two pads (A). STEP 2: remove a LED from the packaging by carefully peeling back the clear plastic film. Identify the cathode end, marked with a small dot (probably green, regardless of LED colour). STEP 3: pick up the LED by its sides, using angled tweezers. STEP 4: place it near the pad where it is to be installed, with the green dot towards the bottom or left side of the PCB (as shown in the overlay diagram of Fig.8). STEP 5: holding the soldering iron in one hand and the tweezers in the other, melt the solder you applied earlier while carefully sliding the LED in place along the PCB surface using the tweezers (B). Stop heating the solder when it is in place but wait a second or two to remove the tweezers, allowing the solder to cool and solidify. STEP 6: if the LED isn’t quite centred or straight, wait a few seconds, then re-heat the solder and gently move or rotate the LED using the tweezers. Repeat until it’s properly centred. STEP 7: apply solder to the other pad (C), ensuring that it flows fully onto the LED pin, which is on the end face of the “chip” that it sits on. STEP 8: wait a couple of seconds for that solder to cool, then add a small amount of additional solder to the other pad, so that it re-flows, forming a neat joint. As you can see from the photos, with some care, it is possible to align the LEDs in neat rows. and one in the centre of the battery meter at lower-right. The procedure for soldering the LEDs is shown in the adjacent panel. With them in place, fit the 14 red LEDs, with 13 on the left side of the rudder display and one at the lefthand end of the battery meter. The 14 green LEDs then go on the remaining pads. If you make a mistake, such as installing a LED backwards, you can remove it by alternately heating its pads while grasping the LED body with tweezers and gently pulling up on it. Eventually it will lift off the board. Clean the excess solder off one of the pads using solder wick before reinstalling the LED. Reed switches The next job is to solder the seven reed switches to the sensor unit’s upper board, coded 20107112. Check it for defects before proceeding and cut out the corners if necessary. Bend the reed switch leads through 90°, 4mm from the glass capsule. This must be done very carefully since the Table 1: Resistor Colour Codes o o o o o o o o o siliconchip.com.au No. 2 3 1 6 1 2 2 6 Value 82kΩ 12kΩ 2.2kΩ 1.5kΩ 1kΩ 390Ω 220Ω 100Ω 4-Band Code (1%) grey red orange brown brown red orange brown red red red brown brown green red brown brown black red brown orange white brown brown red red brown brown brown black brown brown 5-Band Code (1%) grey red black red brown brown red black red brown red red black brown brown brown green black brown brown brown black black brown brown orange white black black brown red red black black brown brown black black black brown August 2011  79 that all seven reed switches are the same height above the PCB. You can then fit the 5mm red LED to the sensor unit control board. This pokes up through a hole in the reed switch board which is not directly above the LED’s pads (see photos). Bend the LED’s leads so that, with the lens pushed fully up through the hole in the upper board, its leads go through the correct holes in the lower board. Make sure they don’t run too close or they could short. The longer (anode) lead must go through the hole towards the bottom of the board. Pin headers These two photos show how the board assembles are stacked together on M3 x 15mm tapped Nylon spacers and secured using M3 x 20mm machine screws and nuts. The interconnections between the two boards in each assembly are made via 12-way pin headers. The sensor module is shown at top, with the display unit below it. glass capsule is delicate, especially where the leads enter it. If any force is applied to the glass body via the leads, it can easily break. The best approach is to clamp the leads with flat nose pliers, right where they exit the glass capsule and then bend the leads down, without touching the glass body at all. To do this, we used Altronics T2770 stainless steel flat-nose pliers, with 4mm wide jaws. If you use narrower pliers, grab the lead slightly away from the capsule to bend them in the right place (ie, 4mm from where they exit the capsule). Both leads must be bent in the same 80  Silicon Chip direction, making a “U” shape. We strongly recommend that you bend the leads perpendicularly to the flat metal reed switch elements, ie, so that when the switch is mounted, the metal leaves inside the capsule are horizontal. This ensures that the switches have a consistent sensitivity to magnetic fields. With the leads bent, install each switch with the horizontal sections of the leads 9-10mm above the PCB (any higher and the lid won’t fit on the box). Start by soldering one lead, then check that the reed switch is perpendicular to the board and at the right height before soldering the other. Make sure Now you can join the lower and upper boards of both units. The first job is to screw them together using two 15mm tapped spacers. Insert a 20mm M3 machine screw through the two top mounting holes of each upper board and thread a 15mm tapped spacer on the end. Hold the spacer with flat-nose pliers and turn the screw until the spacer is tight up against the underside of the board. When finished, the screws will project a few millimetres from the ends of the spacers. Push these through the corresponding holes on the lower board and tighten an M3 nut firmly onto each screw to hold the two boards together. When fully tightened, the two boards are held parallel; see the adjacent photo. Now push a straightened length of 0.7mm diameter tinned copper wire through one of the 12 holes at the bottom until it won’t go any further. For the LED board, solder the wire to the pad on top and trim off the excess. For the reed switch board, cut the wire off flush with the upper PCB and solder it to the pad on the underside (if your reed switch board is double-sided with plated through holes, you can solder it to the pad on the top). Repeat this for the other 11 holes on each board, to form 12-way pin headers. That done, remove the nuts holding the boards together and separate them, then loosen the spacers slightly so that the screws rotate easily. You must also remove the right-most spacer at the top of the reed switch board, leaving just one spacer attached to that board and two to the LED board. Testing the control boards Before completing the assembly it’s siliconchip.com.au a good idea to test the control boards one at a time. To do so, connect a multimeter set to DC amps across the fuse-holder clips and then attach a power supply. If you have a bench supply, set the output to 6V and the current limit to 100mA. Otherwise you can use a battery or another source of appropriate voltage. Turn the power on and check the current flow. After a second or so it should drop below 50µA on its way to 15µA (depending on your meter, it may read 0.0mA). If you get anything above 1mA, cut the power and check for faults. If it’s OK, install the fuse and check the 3/3.3V regulator’s output pin voltage relative to a convenient ground point. It should be within a few percent of the expected figure. If that checks out, cut the power and install the ICs (two for the display unit, one for the sensor unit), orientated as shown in the overlay diagrams. Also plug the 433MHz transmitter in, as shown in Fig.7. You should now insert the jumper shunts for JP1 and JP2 (see Table 1, published last month) to indicate the correct battery/supply voltage for each board. Voltage reference adjustment Both boards need an accurate ADC reference voltage (AREF). This can be measured at tests posts TP1 and TP2. However, the ADC reference divider is normally only powered briefly, to save battery power, so some extra steps must be taken. The sensor unit enables the reference divider for 30 seconds after power is first applied. The display unit does the same but only if its switch contacts (S1) are closed when power is applied. This can be easily achieved by shorting the wires soldered to CON9 using an alligator clip or a blob of solder. For each unit, switch it on while monitoring the test point voltage (TP1 or TP2). Adjust VR1/VR2 to get a reading very close to 2V (say 1.99-2.01V). If this takes longer than 30 seconds, the reference divider will switch off and the reading will suddenly change to be close to either 0V or 3V. In this case, switch the power off and wait a few seconds before turning it on again and finishing the adjustment procedure. When both voltages have been set correctly, remove power and clear siliconchip.com.au Another view showing how the board assemblies are stacked together and connected via the pin headers. Note how the leads of the LED on the sensor control board (top) are bent so that the body of the LED goes through a hole in the sensor board. the short between the leads soldered to CON9. Preparing the boxes The sensor unit requires one small hole to be drilled in its case, for the antenna. Its position is shown in Fig.9. If you are using an external power supply or want to trickle charge the battery you will also need to make a hole for the power connector (either the PCB-mount DC socket or a chassis connector). The cut-out locations for these are also shown in Fig.9. The situation for the display unit is the same except but it also needs a hole for the momentary pushbutton and it has no provision for a PCB-mount DC socket. There isn’t much room inside the display unit for the rear of the pushbutton switch. If it’s located as shown in the drilling template, the rear terminals end up close to the fuseholder but should clear it. So be careful to drill the hole accurately. One option for a power input/charging connector is a 3.5mm jack socket and the drilling template shows an appropriate location to mount one. While these aren’t really sealed against moisture, the stereo switched type has an internal plastic shell which, in combination with some silicone sealant around the hole, should be able to handle a bit of spray. A small IP65 or IP67-rated chassis connector (eg, Jaycar PS0789) would be much better at keeping water out but it will need to have minimal intrusion into the case in order to fit. Once the holes are drilled, test that the components fit through properly. Enlarge them slightly with a tapered reamer if necessary (it’s best to make the holes just large enough, for a tight fit). You can then install and wire up the lower boards. Putting them together Slip the lower boards into the respective cases and secure them with two self-tapping screws, through the two lower mounting holes. For the sensor unit, you can install a third self-tapping screw in the upper-right mounting hole (temporarily unplug the transmitter module). To fit the pushbutton for the display unit, first remove the fuse. Then remove the nut and washer from the button and hold them on the inside of the mounting hole. Thread the button onto them from the outside, then hold the nut with pliers while rotating the button clockwise. Do it up tight to form a good seal and then solder the wires from CON9 to its two tabs. We found the easiest way to do this was to rotate the button so that its tabs were arranged vertically and then solder to the top tab, then undo it half a turn and solder to the other tab before doing it back up half a turn again, for a tight fit. If the tabs are close to the metal parts of the fuseholder you can use a small amount of neutral cure silicone sealant to prevent contact. With the button wired up, replace the fuse. If installing a power input/battery charging socket in either unit, solder short lengths of wire to the tip and August 2011  81 (LID) 1.5mm DIAMETER HOLE FOR ANTENNA WIRE 17 20 105 UPPER LONG SIDE (BOTH UNITS) CL (LID) HOLE FOR POWER INPUT (OPTIONAL) 11 9 9 23 LOWER LONG SIDE (SENSOR UNIT) CL (LID) 12mm DIAMETER HOLE FOR PUSH BUTTON (DISPLAY UNIT ONLY) 10.5 18.5 17 HOLE 6mm DIAMETER, COUNTERBORE 9mm DIAMETER TO HALF DEPTH (OPTIONAL HOLES IN LEFT SIDE FOR BOTH UNITS) 75 Fig.9: follow these three templates to drill and cut the necessary holes in the two cases. Note that the rectangular cutout for the power connector is optional (sensor unit only), as is the 6mm-diameter hole in the side of the case (both units) – see text. sleeve tabs and screw the other ends tightly into the terminal block. Then secure the connector to the case. If the connector is not IP65 or IP67-rated, apply neutral cure silicone sealant around the hole where possible to provide a better seal. The antennas are soldered into place next. First straighten the wires and cut both to a length of 164mm. This is close enough to a quarter-wavelength at 433MHz to give reasonable performance. Scrape the enamel off about 5-10mm at one end of each wire, around the entire circumference, using a sharp hobby knife. 82  Silicon Chip Feed about 15mm of the stripped end in through the hole in each box and use small pliers to bend it to a right angle. Push the wire in further, so that this bent section is against the PCB stake and solder them to each other. Don’t heat it for too long or the wire could melt the plastic box (it should only take a few seconds for solder to adhere to the copper wire). With both antennas soldered in place, bent the sensor unit’s antenna so that it sticks straight up with the box lying flat on its back. The display unit’s antenna is left as is. To reduce the chances of eye injury, a small plastic wire joiner (or another small, smooth plastic object such as a sphere with a hole drilled in it) must be glued to the end of each antenna. Fill the wire joiner with hot-melt glue or neutral-cure silicone sealant and push it over the end of the antenna. Do this for both units and once the adhesive has set, trim off any which has leaked out. It’s also a good idea to seal the antenna hole on the inside of the case to prevent moisture ingress. If you are going to power either unit with a battery, install it now. Then fit the upper boards by carefully lining each pin header up with the socket on the appropriate lower board and pushing the upper board down into place. The upper reed switch board is fitted to the lower board with the small, horizontal transmitter module while the LED board goes on the display unit which has the larger, vertically mounted receiver module on the righthand side. Push down on and tighten the mounting screws at the top (one for the sensor unit, two for the display unit). The screw threads pass through a hole in the lower board and into the plastic bushes moulded into the bottom of the case. If you don’t feel the thread gripping then the screw may be misaligned. Check that the upper boards are parallel with the bases before screwing the lids in place. Testing Apply power to the sensor unit, then wave the magnet close to its reed switches (without touching them). The red LED should light each time a reed switch closes (this may result in a soft click). If it doesn’t work, loosen the screw on the upper board and pull it out using pliers (or slide a thin item under the edge and pry it up). Remove the upper board and check that its pin header was properly connected; if so, the fault is likely on the lower (control) board. Assuming the sensor unit works, apply power to the display unit and press its pushbutton. One or two LEDs of the battery level meter should light up. If not, remove the upper board and check the pin header alignment and for faults in the control board. It’s also possible that one or more LEDs have been installed backwards. Now with both units powered up, siliconchip.com.au separate them by one metre or more and move the magnet over the reed switches. The corresponding rudder position LEDs should light up. If the units are too close together, the wireless link won’t work because the input stage of the receiver unit overloads. Once you’re satisfied that everything is working properly, hold down the display unit’s pushbutton for a second or so to turn it off. MAGNET (UNDER ARM) S2 RUDDER BEARING S3 © 2011 S4 SC S5 SENSOR UNIT CON6 S6 S7 siliconchip.com.au ADDED ARM CON5 A photo on the following page shows how we installed the sensor unit in our test boat. It is set up so that the magnet hanging from the rudder arm is centred on the reed switches and sweeps from the first to the last as the rudder is moved over its full angular range. The dimensions of the horizontal arm used in our installation are shown in Fig.11. We initially attached the sensor unit, arm and magnet using foamcored double-sided tape, to check that the positioning was all correct before making a more permanent installation. We suggest that you do the same. In fact this tape can give a surprisingly strong bond and may be suitable for the final installation. If not, a strong epoxy such as JB Weld can be used to hold the arm to the rudder shaft once the alignment is correct. Since different boats will vary in terms of their rudder angle, bearing size and so on, you will need to measure yours and make adjustments to the dimensions. If your rudder arm has a larger sweep angle (this one has a full sweep of about around 60°), mount the sensor unit closer to the shaft and shorten the arm. If it has a smaller sweep angle, mount it further away and lengthen the arm. The idea is to ensure that the magnet is over one of the end-switches at full lock. The sensor unit can be mounted at any position around the rudder shaft but it should be orientated so that a line drawn through the central reed switch would pass through the centre of the rudder shaft. The arm’s vertical offset should be selected so that the magnet is just above the top of the sensor unit’s lid. If there’s too much of a gap between the magnet and the lid, the reed switches may not operate reliably due to a low magnetic field strength. The magnet is a type designed specifically for triggering reed switches HYDRAULIC RAM RUDDER ARM S1 Installation ACTUATOR PIVOT (HORIZONTAL PLATFORM) RUDDER Fig.10: repeated from last month’s article, this diagram shows how the sensor unit is arranged. It’s mounted on a platform and is activated by a magnet on the underside of an arm that’s attached to the rudder shaft. 88 20 (MAGNET ASSEMBLY) 24 METAL ARM IS 2mm THICK, 12mm WIDE DOUBLE-SIDED ADHESIVE TAPE ALL DIMENSIONS IN MILLIMETRES Fig.11: the arm that’s used to attach the magnet to the rudder shaft can be fabricated as shown here. Note that the dimensions may need to be altered to suit your particular installation. We secured the magnet assembly using double-sided adhesive tape but a strong epoxy adhesive could also be used. and we found that this works much better than other magnets, even the strong rare-earth types. You may find it necessary initially to insert a shim between the arm and magnet to adjust its height and get the unit’s response just right. Or depending on the material your crank arm is made from, you may be able to bend it to make adjustments. We used a curtain bracket for our cranked arm which happened to have dimensions that were pretty close to what we needed. You may be able to find a standard bracket to suit your needs but otherwise, cut a piece of aluminium to size with a hacksaw, file its edges clean and bend it in a vice. Range As stated last month, the reliable operating range for these units is at least 20m. We have confirmed that this figure is realistic on a boat. With our installation, the receiver not only operates anywhere on the boat but it also August 2011  83 The sensor unit is shown here mounted in the lazarette (a compartment under the rear deck of the boat), with the Ultrasonic Anti-Fouling Unit (SILICON CHIP, September & November 2010) immediately to its left. Note how the arm (which carries the magnet) is attached to the rudder shaft. Make sure that the control arm is clear of any obstacles over its full range of travel. on, it will show the rudder position once it is changed by moving the wheel (ie, when a reed switch closes). To change the LED brightness, tap the pushbutton. It will cycle through the three possible settings. When you are finished, switch the display unit off by holding down the pushbutton for a second or so. If you forget, it will switch itself off after about 15 minutes of inactivity (ie, if no valid packets received). While the display unit is portable so that it can be carried between helm positions, it is probably a good idea to install some kind of bracket which can hold it in place while you are steering. This view shows the completed display unit mounted in the wheelhouse of a large power boat. The indicator LEDs are very bright, even in daylight works on boats berthed alongside. This is using the whip antennas described here, even with the sensor unit inside an enclosed lazarette compartment. If you need more range, you can run a coaxial cable to an antenna installed outside the compartment. The simplest method is to install a chassis-mount RCA connector in place 84  Silicon Chip of the antenna wire, with the inner pin soldered in place of the PCB stake and its metal tab wired to the adjacent ground pad (not normally used). You can then run a coaxial cable to the external 433MHz antenna. Using it After you switch the display unit Power loss If the transmitter unit loses power, eg, when the battery is changed, it will create a new unique identifier. Unless the display unit is also reset, it will ignore transmissions with the new identifier as they do not match that stored in its memory. In this case, you must remove power from the display unit (eg, by taking the battery out and putting it back in) and then it should SC work normally again. siliconchip.com.au