This is a kit of the no-moving parts Wind Speed Meter published in the UK electronics magazine Everyday Practical Electronics, January, 2003, pages 44 to 51. A copy 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 2×16 LCD fits on top of the main PCB. The schematics have been redrawn but we have kept the same Component Designators. An Off/on switch and input protection diode have been added.
Ten mm nylon standoffs in each corner raise the PCB and allow the two switches S2 and S3 to come out. Also access to VR1 and VR2 is easy since both trimpots are mounted underneath the PCB. Access to test points with a CRO is also easy with this arrangement. We did not keep the In Circuit Programming header.
Assembly. There are two links to add to the board. Add the lowest height components first. The two trimpots are mounted under-neath the PCB. Pads labelled 12 and 13 under the PIC firm-ware are for switches S2 and S3 resp. (Remember pin 12 for S2; pin 13 for S3.) Add about 6″ of wire from these pads and the two GND pads provided. S2 and S3 are needed for testing and minor calibration later. Label the two switches.
Do not attach the 9V battery snap for the moment. Do the testing with the a power supply using the power jack center-positive input. Add the 16 pin male connector and the two 18mm screws to the LCD as shown. After mounting add the third screw to each leg to secure the LCD in place.
Ultrasonics assembly. Mount the two ultrasonic transducers faces 18 cm or 6 7/8″ apart. We used araldite and mounted them on a pair of unbroken wooden chopstocks. The software is written for this spacing so I suggest 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 the assembly 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. No track needs to be kept of which is the Tx and which is the Rx. See the EPE article for more details on this.
Firmware. We used the code as supplied by EPE. However, there was a small bug in it. The second and third last lines of the hex file needed interchanging with changes to the line numbering and check digits.
Testing. Now is the time to read and follow the EPE article. 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 in the 2pm to 2.30pm position we got the best stability. (See photo.) This meant that the pot was biased about 15K ohm to the R8 resistor and 85K ohm to pin 1 of IC4.
2. We needed a correction of -3 on the correction mode screen 3 on our prototypes in order to get 0 0 0 1 0 0 readings when S2 was pressed and the sensors were in still air..
K168. EPE WIND SPEED METER
Note what is written on page 50: There will always be a bit of value changing seen, due to the simple nature of the transducers 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 the waveforms 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.
Spurious Readings. If you find that you are getting a stream of about 6 correct readings followed by one very wrong 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 a slight change or maybe a big change in the P2 position to get a 1 2 1 1 2 on the right hand side. I have found there are several positions (at around the 2.30pm position) where there are minimum readings. Some of them seem to give more spurious readings than other positions. I have usually found that I can get one position which does not give spurious readings.
Alternatively you can press S3 and go to averaging mode as described in the EPE article. That evens out the spurious readings.
Permission. This kit has been used with permission from Everyday Practical Electronics. The PCB has been completely redesigned. The software is used as supplied by EPE with one bug correction.