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Our weathervane came from a commercial unit sold by a mail order company but you could also adapt one from a garden supply shop. The wind direction is indicated on the LED display unit pictured below, which has 16 LEDs arranged around a compass. Build an accurate wind vane with a 16-LED display How would you like to know the wind direction at any time, day or night? Build this electronic wind vane and its display to indicate the wind direction from any of 16 points on the compass. No longer do you have to go outside – just look at the LED display. By JOHN CLARKE 40  Silicon Chip Did you build the nifty wind speed indicator published in the March 1999 issue of SILICON CHIP? That design was based on a bicycle computer and was quite popular. In fact since then we have had quite a few requests for a companion electronic wind vane. And here it is. A common approach to building an electronic wind vane is to use a circular array of reed relays. The wind vane is attached to a disc and magnet and when it comes close to a reed relay, it actuates to drive a LED to indicate a particular wind direction. While that is a simple approach, it does have its limitations and it does become unwieldy if you want to indicate more than eight wind directions – you need a lot of reed relays and a lot of cabling from the wind vane itself to the LED display panel. With that in mind, we set out to produce a design which would indicate wind direction from 16 points of the compass and which would use a modest amount of electronics to eliminate the need for a thick multi-way cable. By the way, when we say 16 points of the compass, it means that the accuracy with which you can measure the wind direction is within 22.5°. In other words you Fig.1: the basic scheme for the Electronic Windvane. Depending on the position of the Gray encoded disc, the IR detectors pick up light from the IR LEDs and this information is decoded by IC1 and fed to the display. will be able to distinguish between a Nor-Easterly and a Nor-Nor-Easterly and so on. The Electronic Windvane comes in two parts, one to house the wind vane detector circuitry and the second to house the display circuitry. The readout on the display comprises 16 LEDs to display the directions N, S, E, W, NE, NW, SE and SW and the intermediate points NNE, NNW, ENE, WNW, SSE, SSW, ESE & WSW. Infrared LEDs and diodes Fig.1 shows the general arrangement of the circuitry in­volved. The detector comprises four infrared LEDs and four in­ frared detector diodes. They are aligned in two rows, with LED1 shining on IRD1, LED2 shining on IRD2, etc, with a translucent encoding disk located in between them. The disk is made of PC board material and comprises four concentric rings, one for each diode and detector pair. The rings have sections of copper to block the light transmission and sections of translucent board to allow the light to pass. Depending on whether or not light is shining on them, the four infrared diode outputs have two possible states (0 or 1) to provide us with 16 combinations corresponding to the 16 Fig.2: the complete circuit diagram for the Electronic Windvane. The position of the Gray encoded disc depends on the direction of the wind and this in turn determines which of the IR detectors (IRD1-4) picks up light from its companion LED. IC1 decodes the detector outputs and drives the direction indicator LEDs. March 2000  41 Fig.3: this diagram shows how the major parts are assembled inside the plastic case. The Gray encoded disc (board 3) sits between the IR LEDs on board 2 and the IR detectors on board 4. an incorrect direction reading as we move from one code to another with each change in direction. The 4-bit outputs from the detector diodes are applied to the 4-16 decoder. This is a binary decoder which does not decode in the Gray sequence but it is simple enough to rearrange the decoder outputs so that the correct directions are obtained on the LED display. Circuit description compass points. The ring pattern on the disc is shown in the PC patterns of Fig.7, toward the end of this article. Gray code The ring encoding on the disc is such that only one of the detector outputs changes state for any single change in direction. The 16 possible codes are shown in Table 1, together with the equivalent decimal value. Note that the numbers do not count in a standard sequence from 0 to 15 but are jumbled. By studying the table you will see that only one digit in the 4-bit code changes between each successive number. This type of encoding is called a Gray code (after Elisha Gray) and it ensures that we will not obtain Fig.2 shows the complete circuit and as you can see, there is not much to it. The four infrared LEDs (IRLED1IRLED4) are connected in series and powered from the 12V supply via a 1.8kΩ resistor. This allows about 2-3mA of current through the LEDs. The IRLEDs shine on to their respective infrared detector diodes (IRD1-IRD4) which are reverse biased between the positive supply and ground via 10kΩ resistors. When an IRD does not re­ceive any light, its anode voltage is pulled low via its respec­tive 10kΩ resistor. When light shines on the IRD, reverse current flows, from cathode to anode, and the voltage at the anode goes high. The four anode outputs connect to the A, B, C & D inputs of IC1, the 4514 decoder. The most significant bit is the D input and the least significant bit is the A input. The 16 outputs drive the display LEDs but only one is lit at a time. If the A, B, C & D inputs are all low, then the “0” output at pin 11 goes high to drive the North LED (LED1). Similarly, if only the A input is high, the “1” output goes high and drives the NNE LED. Current through Table 1: The Gray Codes Decimal B inary Decimal B inary 0 0000 12 1100 1 0001 13 1 1 01 3 0 0 11 15 1 1 11 2 0010 14 1110 6 0110 10 1010 7 0 1 11 11 1011 5 0 101 9 1001 4 0100 8 1000 Table 1 above shows the 16 codes that are encoded onto the disc, while the photo at left shows the corresponding ring pattern on the board. Note that only one digit in the 4-bit code changes between each successive number. 42  Silicon Chip Fig.4: install the parts on boards 2 and 4 as shown here, making sure that the IR LEDs and detectors are correctly oriented. It’s a good idea to used PC stakes at the external wiring points, as this will make the wiring easier. the powered LED is limited by the common 2.2kΩ resistor. Power for the circuit is derived from a 12V DC plugpack and diode (D1) prevents damage to the circuit if it is connected the wrong way around. The 47Ω resistor and zener diode ZD1 limit the voltage to 15V. The 100µF capacitor decouples the supply. Construction While the circuit is simple, the construction is more com­ plicated. There are four PC boards and two cases involved. The display board, board 1, coded 04103001, can be mounted in a plastic case or as we did, in a circular wooden enclosure 131mm in dia­meter. It could be salvaged from an old barometer or turned up if you have a wood lathe. Alternatively, you can pur­chase one from the supplier mentioned in this article. It in­cludes provision for a glass or Perspex window in front of the display. Boards 2, 3 & 4, coded 04103002, 04103003 & 04103004 are for the position detector circuitry and are housed in a weatherproof plastic case measuring 115 x 90 x 55mm. You can start work on the PC boards by checking for shorts or breaks in the copper tracks. The Gray encoding PC These are the completed position detector circuit boards, ready for assembly into the case. Note the metal bushes which have been soldered to boards 3 and 4 (just visible from the top). March 2000  43 board (code 04103003, board 3) will need to be cut into a circular shape. The corners will also need to be removed from board 2 (code 04103002) to allow access to the retaining screws which ultimate­ ly hold the PC assembly in the case (see Fig.3, which shows the mechanical assembly of the PC boards). The corner holes for the three other boards should be 3mm in diameter while the centre hole in board 2 should provide clearance for a 6mm rod. The centre holes in boards 3 & 4 (04103003 and 04103004) should be reamed out to provide an inter­ference fit for brass bushes which fit over the 6mm (or 1/4-inch) rod. Four brass bushes with grub screws will be required. These can be obtained from plastic knobs. OK. So you get four of these knobs, remove their grub screws and then squeeze them in a vise to crack the plastic housing. Remove the bushes and re-insert the grub screws so you do not lose them. Ream out the holes in boards 3 & 4 so that the bushes are an interference fit. The bushes are then pressed into the copper side of the PC boards and soldered into place. Do not press the bush for Board 3 in too far otherwise you will not be able to tighten the grub screw. You will need a rod 150mm long to suit the bushes and this may be 6mm or 1/4-inch in diameter. Test fit the rod in the bushes in the board and ensure that all run freely and true (without wobble). That done, you can assemble the electronic components onto each board. The component overlays are shown in Fig.4 & Fig.5. Start by soldering in the PC stakes which are located at all the wiring points, then install the links and resistors. Table 2 shows the colour codes. Make sure you install diode D1, zener ZD1 and the 100µF capacitor the correct way around. Similarly, when inserting IC1, be sure to orient Fig.5: the main display board carries the 16 direction indicator LEDs and the decoder IC. Make sure that these parts are all oriented correctly. Table 2: Resistor Colour Codes      No. 4 1 1 1 44  Silicon Chip Value 10kΩ 2.2kΩ 1.8kΩ 47Ω 4-Band Code (1%) brown black orange brown red red red brown brown grey red brown yellow violet black brown 5-Band Code (1%) brown black black red brown red red black brown brown brown grey black brown brown yellow violet black gold brown The wooden display housing is drilled to accept the LEDs, using the label as a template. This shows the rear view but note that the unit should be drilled from the front. it correctly before soldering in place. The infrared LEDs (IRD1-IRD4) are coloured smokey blue and are inserted into board 2 (code 04103002). Note that the anode lead is the longer one and these LEDs must be inserted with the correct polarity. Solder them so that the height from the top of the LED above the PC board is 14mm. The infrared detector diodes (IRD1IRD4) have clear lenses and are inserted into board 4 (code 04103003) with a height of 14mm above the board surface. Do not insert the 3mm red LEDs for the display PC board just yet. You are now ready to assemble the three wind detector boards as shown in Fig.3. Insert the rod into the bush of board 4 and fit another bush onto the rod to stop it from moving through the board. These two bushes become the lower thrust bearing for the wind vane. Now place board 3 onto the rod together with another bush and a washer. Secure board 2 in position using the 25mm and 6mm spacers and 3mm screws. Make sure that the IRLEDs and IR detector diodes are lined up directly opposite each other., then tighten the grub screw for board 3 so that it is positioned centrally between the infrared LEDs and diodes. Set the upper bush with a little clearance between it, the washer and top board so that the rod can spin freely. A drop of oil on the lower bushes will allow a freer movement. Attach The display board is mounted on the back of the housing using 6mm spacers and 10mm-long wood screws. A cable clamp is used to anchor the leads. the lower PC board to the base of the case with 3mm screws or self-tapping screws. The lid of the case can be drilled in the centre to accept a threaded bush from a rotary switch or potentiometer. The 6mm rod should fit neatly through this threaded bush. Also drill out the hole in the side of the box for the cable entry and grommet or cable gland. The lid of the case should have the supplied gasket fitted into the grooving, so that it will be weatherproof. Display housing The diagrams showing how the display board is housed in a plastic case or circular wooden enclosure are shown in Fig.6. If you are installing it in the plastic case, you can tack solder the LEDs on one lead only with the top of the LED being 27mm above the PC board. Then insert the board on 12mm long standoffs and secure with screws into the base of the case. Attach the label to the lid of the case and drill out the holes for the 16 LEDs. Note that although we have marked one LED as the North LED, this is arbitrary. Any LED can be chosen as the North LED and so the label can be oriented in any way to suit the case you have. Place the lid on the case and check that the LEDs are just protruding through the label. You may need to readjust the LED height before finally The front panel label is glued to an aluminium disc and the holes then drilled around its circumference so that is fits over the indicator LEDs. If you wish, the label can be protected using an acrylic or glass faceplate. March 2000  45 Fig.6: these two diagrams show how the display board is mounted in a plastic case (top) or in a wooden case (above). If using the wooden case, the LEDs are first mounted on the PC board, then the board is mounted in position and the LEDs pushed through the holes in the case before soldering. soldering all the leads in place. The wooden enclosure can be drill­ ed for the 16 LEDs in the front face using the label as a guide. Push the LEDs through the holes and secure the PC board to the case using 6mm The 6mm metal rod passes through a 6mm threaded bush which is attached to the case lid. This bush can be obtained from a rotary switch or a potentiometer. 46  Silicon Chip standoffs and wood screws as shown. Solder the LEDs in position. This done, remove the PC board and attach the label to the face of the enclosure. Again it does not matter which orientation you choose for the North LED. You can place a circular acrylic or glass face in position over the label if required. Wire up the boards as shown using 6 or 8-way cable. This cable must be long enough to extend from the position detector circuitry to the display board. Initially, the wiring will prob­ ably be only temporary since you will need to install the weather vane on a mast and the display case inside your home. We envisage that the wiring between the two would be passed through the wall and up to the mast. Attach the wires for the 12V DC plugpack supply to a DC line socket and connect up the supply. You should be immediately greeted with one LED alight. If you rotate the rod on the posi­tion detector, the LEDs should each light up in sequence. If the LED order is jumbled, then you possibly have the wiring to the A, B, C & D terminals mixed up. If the North position appears to have a greater range of movement before the adjacent LEDs light, you can reduce the value of the 1.8kΩ resistor for the IRLEDs. This will produce more light from the LEDs to reduce the shadow effect caused by the transition from dark to light as the coding on the Gray disc changes from copper to translucent PC board material. Increasing the current through the IRLEDs will reduce the range of movement that the rod moves with the North LED alight. Note also that the circuit is de­ signed to operate in the dark; ie, with the circuit in its box. If you test the as­ sembly in daylight or artificial light, the detectors will not work properly. Weather vane We adapted our weather vane from This is what the unit looks like before the bottom of the case is attached and the weathervane fitted. The skirt of the plastic hose fitting covers the threaded bush (to keep water from running down the shaft) but sits slightly proud of the case so that the shaft can turn. Note the plastic sleeve over the shaft. a commercial unit made of plastic and supplied by the mail order firm Magnamail. We just used the plastic arrow without the clip-on bird (well, it was an eagle instead of a proper rooster!). We also used a plastic snapon tap hose fitting which prevents water running down the rod and into the box via the top bush. Both the tap fitting and plastic wind vane were internally sleeved with Nylex plastic tubing which made them a friction fit onto the metal rod. Calibration Use a compass to find North. Set the rod on the position detector so that Parts List 1 PC board, code 04103001, 89 x 81mm 1 PC board, code 04103002, 89 x 81mm 1 PC board, code 04103003, 69 x 69mm 1 PC board, code 04103004, 89 x 81mm 1 weatherproof plastic box, 115 x 90 x 55mm 1 circular wooden display case, 131mm diameter (see panel) 4 6mm untapped spacers 5 10mm long wood screws 1 cable clamp (see text) OR 1 plastic case, 115 x 90 x 40mm 4 12mm untapped spacers 4 M3 x 20mm screws 1 6mm ID rubber grommet 1 display label, 71mm diameter 1 12VDC plugpack 1 DC line socket 1 150mm long 6mm or 1/4" metal rod 4 plastic knobs with 6mm brass bushes and grub screws 4 25mm tapped brass spacers 4 6mm untapped brass spacers 8 M3 10mm screws 4 M3 6mm self-taping screws to mount PC board in case 1 6mm brass washer 1 6mm threaded bush (from rotary switch or potentiometer) 16 PC stakes 1 120mm length of 0.8mm diameter tinned copper wire 1 length of 6-way or 8-way cable (for windvane sensor to display) 1 6mm ID rubber grommet or cable gland 1 100µF 16VW PC electrolytic capacitor Semiconductors 1 4514 CMOS 4-16 decoder (IC1) 16 3mm red LEDs (LED1-LED16) 4 5mm infrared LEDs (IRLED1IRLED4) 4 5mm diameter infrared detector diodes (IRD1-IRD4) 1 1N4004 1A diode (D1) 1 15V 1W zener diode (ZD1) Resistors (1%, 0.25W) 4 10kΩ 1 1.8kΩ 1 2.2kΩ 1 47Ω Miscellaneous Solder, weathervane, mast, plastic hose fitting, plastic sleeving, etc. March 2000  47 Fig.7: here are the full-size artworks for the four PC boards and for the front panel artwork. The boards should all be correctly drilled and the corners trimmed as shown before installing any parts. the North LED is alight and is in the middle of its angular travel between where the NNE or NNW LEDs light. Now point the weather vane towards North, make sure that it is not loose and you’re done. We fitted the underside of the wind vane case with a flange intended for a shower curtain rod. This makes it easy to mount on SC top of a wooden dowel or metal pipe. Where To Buy The Wooden Display Case The circular wooden display case can be purchased from Mr Rod Chambers, PO Box 18, Moonbi 2353. Send cheque or money order to the value of $15 plus $5 p&p. 48  Silicon Chip