Ultrasonic Wind Speed Meter

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  K168. EPE WIND SPEED METER  This is a Kit of the no-moving parts Wind Speed Meter  published in the UK electronics magazine EverydayPractical Electronics, January, 2003, pages 44 to 51. Acopy of the article is included with the kit since the Meter  performed almost exactly as described in the article.We have redrawn the PCB so that the 2x16 LCD fits ontop of the main PCB. The schematics have been redrawn but we have kept the same Component Designators. AnOff/on switch and input protection diode have beenadded.Ten mmnylonstandoffsin eachcorner raise thePCB andallow thetwoswitchesS2 andS3 tocomeout. Also access to VR1 and VR2 is easy since bothtrimpots are mounted underneath the PCB. Access to test points with a CRO is also easy with this arrangement. Wedid not keep the In Circuit Programming header. Ultrasonics assembly. Mount the two ultrasonictransducers faces 18 cm or 6 7/8” apart. We used aralditeand mounted them on a pair of unbroken woodenchopstocks. The software is written for this spacing so Isuggest you do the same for your first model.Make sure they face each other squarely. When set we joined the two earth pins with green wire. Connect theassembly to the PCB using three wires: GND, X4 and X3.You can use the pins provided or solder direct to the pads. Note each ultrasonic transducer is treated the same. Notrack needs to be kept of which is the Tx and which is theRx. See the EPE article for more details on this. Assembly. There are two links to add to the board. Addthe lowest height components first. The two trimpots aremountedunder-neath thePCB. Padslabelled 12and 13under thePIC firm-ware arefor switchesS2 and S3 resp. (Remember pin 1 2 for S 2 ; pin 1 3 for S 3 .)Add about 6” of wire from these pads and the two GND pads provided. S2 and S3 are needed for testing andminor calibration later. Label the two switches. Firmware. We used the code as supplied by EPE.However, there was a small bug in it. The second andthird last lines of the hex file needed interchanging withchanges to the line numbering and check digits. You canget the asm and correct hex file from our website athttp://www.kitsrus.com/zip/k168code.zip  Photos. You can download the color jpg’s of the photosin this documentation from our website athttp://www.kitsrus.com/jpg/k168_x.jpgDo notattach the9V batterysnap for themoment.Do thetestingwith the a power supplyusing the power jack center-positive input. Add the 16 pin maleconnector and the two 18mm screws to the LCD asshown. After mounting add the third screw to each leg tosecure the LCD in place.where x is 1 to 6. Testing. Now is the time to read and follow the EPEarticle. We will not repeat the setup and testing here but just stress some points we found.1. Getting trimpot VR2 (P2) set was a bit tricky.However, we found that when the trimpot was inthe 2pm to 2.30pm position we got the beststability. (See photo.) This meant that the potwas biased about 15K ohm to the R8 resistor and85K ohm to pin 1 of IC4.2. We needed a correction of -3 on the correctionmode screen 3 on our prototypes in order to get 00 0 1 0 0 readings when S2 was pressed and thesensors were in still air..  K168. EPE WIND SPEED METER  Spurious Readings. If you find that you are getting astream of about 6 correct readings followed by one verywrong reading (like 3mph, 3.4 3.6 3.1 3.2 19.5 3.4 3.5… )then try recalibrating P2 just a little. Press S2 and make aslight change or maybe a big change in the P2 position toget a 1 2 1 1 2 on the right hand side. I have found thereare several positions (at around the 2.30pm position)where there are minimim readings. Some of them seem togive more spurious readings than other positions. I haveusually found that I can get one position which does notgive spurious readings. Note what is written on page 50: ‘There will always be a bit of value changing seen, due to the simple nature of thetransducers and the amplifier’.Wind pulse and wind mask we had no reason to change.If you have a CRO you can investigate the details of thewaveforms and triggering as discussed in the article.We have made pads under the board to solder a 9V battery snap when you want to take the meter out in your car to test.Alternatively you can press S3 and go to averaging modeas described in the EPE article. That evens out thespurious readings. COMPONENTS Resistors 5%,1K brown black red R1 R11 24K7 yellow violet red R8 110K brown black orange R3 R7 R9 R10 4 Permission. This kit has been used with permission fromEveryday Practical Electronics. The PCB has beencompletely redesigned. The software is used as supplied by EPE with one bug correction.47K yellow violet orange R2 1100K brown black yellow R4 R5 21M brown black green R6 110K Koa trimpot 103 P1 (VR1) 1100K Koa trimpot 104 P2 (VR2) 1 pins 31nF ceramic C7 110p ceramic C3 C4 C9 3100p ceramic C5 11N4004 D1 11N4148 D2 1BC548 TR1 120.000MHz crystal 49S X2 1100n 104 mono .1 C1 C2 2100n 104 ceramic C6 C8 22.6mm x 18mm screw 22.6mm nuts 69V battery snap 1Push-on switch S2 S3 2SPDT switch S1 1 Nylon standoffs 4Power Jack X1 140kHz ultrasonic transducers X3 X4 1 set4052 IC IC3 116F628-20/P IC1 1LM358 IC4 18 pin IC socket 116 pin IC socket 118 pin IC socket 116 pin male connector 116 pin female connector 116x2 LCD no back light 1K168 PCB 1Like John Decker we tried ultrasonic transducers withsolid metal fronts (400ER180 and 400 ET180) but ininitial trials they did not seem to work. However, thisneeds more experimenting.  K168. EPE WIND SPEED METER  These schematic files may be downloaded fromhttp://www.kitsrus.com/jpg/k168_1.pcx http://www.kitsrus.com/jpg/k168_2.pcx 
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