WxImp Parts List
- A small DC electric motor is used as a generator for the anemometer. Originally I used the F-K20 3v motor popular in model planes, however I wasn’t happy with the performance of the anemometer in very low wind conditions. A Uxcell 7mm motor is easier to mount and seems to perform better at low wind speeds. The plastic gear that comes pre-installed also makes it easier to install in the Anemeometer hub. Uxcell appears to make a wide range of small dc motors. You should be able to use many of these by printing a simple motor mount of your own design.
- To get a better match between the output range of the motor and the input range of the analog-to-digital converter in the Imp (at least at sub-hurricane wind speeds), I’ve added a small op-amp circuit mounted in the tube that supports the motor. See the Anemometer Wiring page for details. It consists of an LM358 op-amp, two resistors and a pair of 0.1uf disk ceramic capacitors to help with noise suppression. You can either build it on the pins of the op-amp or grab the Gerber files for a little printed circuit board from the same Github repository as the the WxImp code. JCLPCB will make 10 prototype boards for $2 and they offer free shipping for first time customers.
- To connect the generator to the Imp Explorer you’ll need a Grove sensor cable. Actually you’ll only need half of one… more info in the wiring instructions.
- You need four plastic soda straws. If you don’t already have some, try your local grocery store, or a nearby Target store.
- You can’t get accurate air temperature or relative humidity readings if your WxImp is in full sun, so if you don’t plan to mount it in a spot that’s always shaded, you’ll need about a 10-inch disk of some rigid weatherproof material for a sun shade. Coroplast corrugated plastic is what we’re using. It’s available from Amazon, but try your local art supply store first.
- You need 3 AA batteries or a USB power supply to power the WxImp. I’m running NiMH rechargeables. If you are in a very cold climate you may get better results with lithium primary cells which are rated to work down to -40°F. There’s still testing to do, and the capacity of different battery types varies, but with the WxImp reporting data once per minute, battery life appears to be at least two weeks.
The rest of the parts you need to complete the project are all 3D prints. See the Wximp 3D Printing Notes