Construction of the weather station Sensor Grenade Bill Ellis N5ZTW April 2, 2001

Transcription

1 Construction of the weather station Sensor Grenade Bill Ellis N5ZTW April 2, 2001 I designed and built a prototype Grenade to house the humidity and temperature sensors for my 1-Wire weather station. It is designed using materials found at your local hardware store or home center. It should cost about $5-6 to build. This design allows air to enter the grenade but places the sensor PC board up above any chance of getting wet from rain. Drain holes allow any rain that my blow in to drain out and a screen system prevents pesky insects from thinking it a fancy new condo. Materials: 2 Sch 40 PVC Cap Home Depot p/n $.68 2 Sch 40 PVC Coupling Home Depot p/n $.62 2 to ¾ Sch 40 PVC Reducing Bushing Home Depot p/n $ Sch 40 PVC pipe 1 ¾ long ½ Sch 40 PVC pipe 2 long ¾ Elect PVC Terminal Fitting Home Depot p/n $.22 ½ Elect PVC Terminal Fitting 6 ¼ x 1 ¾ patch of window screen 2 ½ x 2 ½ patch of window screen PVC pipe cement

2 Tools: Hacksaw Drill 1/8 drill bit ¼ drill bit Scissors Pencil Sanding paper Small brush Instructions: 1. Scrape off the labels from all PVC parts with your fingernail. Clean off the sticky residue with some rubbing alcohol. 2. Press the 2 to ¾ bushing into the 2 coupling. I put mine on the opposite end of the coupling than the little finger left by the plastic injection process. (Not critical, see step 20) Mine was very tight so I did not use glue. 3. Cut a piece of 2 PVC pipe 1 ¾ long. Press this piece into the other end of the coupling. Again mine was tight and did not require glue. The two parts won t meet. You will have about a 1/8 gap inside the coupling between the bushing and the pipe. 4. Place the assembly pipe side down on the bench. Drill two 1/8 holes trough the bottom of the bushing in each of the four pockets Total eight holes. See figure 1, These are the water drain holes. 5. Using the pencil mark a ring around the coupling 15/16 from the bottom of the coupling edge (bushing side) 6. Drill eight 1/8 holes on this line around the coupling. Center each hole with the flats on the bushing. You will be drilling through both the coupling and the bushing. 7. Draw another line around the coupling 15/16 from the coupling edge on the pipe end. 8. Drill eight more 1/8 holes on this line centering each one between the first set of holes. Again you will be drilling through both the coupling and the pipe. 9. Open all 16 1/8 holes in the coupling to ¼ with the drill. See figure 2 Do not open the water drain holes in the bottom of the bushing!

3 Figure 1, 8-1/8 Water Drain holes Figure 2, ¼ Air holes 10. Cut two pieces of window screen. One 6 ¼ x 1 ¾ (critical dimension) and another 2 ½ x 2 ½ set aside. 11. Sand the inside of the chamber to remove any fuzzies from all 24 holes in the chamber. 12. Cut the 2 ½ x 2 ½ screen into a perfect 2 circle. In the center of this circle cut a circle 1 3/16. These dimensions are critical. You should now have a 2 screen doughnut 13. Cut a 1 ¾ long section of ½ PVC pipe and glue it in the ½ Elect PVC Terminal Fitting to form the core see figure Place the doughnut in the bottom of the chamber. Ensure that all eight water drain holes in the bushing are covered. Place the core you just built down into the center hole of the bushing, terminal fitting first. Ensure the terminal fitting can rest on the PVC of the bushing and not on any of the screen doughnut. Trim the doughnut accordingly. Do Not glue the core in at this time. 15. Now the tricky part: Using the PVC cement and a small brush put a light coating of cement on the bottom of the chamber covering the eight holes. I used my finger but you should use a brush. You should not use the brush from the PVC glue bottle as it will make a huge mess. 16. Let the glue dry for about 30 seconds until tacky and place the doughnut inside pressing it down on the tacky surface. Let dry. 17. Now put a light coating of cement on the inside wall of the chamber 1 ¾ around the bottom. Remember no drips of cement on the doughnut screen below, go light on the cement! 18. Let the glue dry for about 30 seconds until tacky and place the 6 ¼ x 1 ¾ screen over the holes pressing it down on the tacky surface. Let dry.

4 19. Now glue the core into the inside of the chamber. See figure 4. The terminal fitting will be loose. You will be gluing the flat surface of the fitting to the bottom of the chamber (bushing). Again don t use so much glue as to drip and clog the holes in the screen. HINT: You may want to screw the ¾ terminal fitting into the bottom of the grenade first, in case any glue drips onto the threads making them tough to use. Figure 3, Core Assembly Figure 4, Core installed (note: screen not shown) 20. Place the PVC cap on top. Mine was fairly loose so I aligned the little fingers left by the plastic injection process on both the cap and the coupling. I then drilled a #29 hole trough both the cap and the pipe 3/8 from the finger and ¼ from the bottom of the cap. I then opened up the cap hole with a #19 drill and tapped the #29 hole in the pipe with an 8-32 tap. See Figure 5 This is optional. I did it to hold the cap in place with a stainless steel screw. Figure 5, Cap alignment and screw hole Figure 6, Grenade Mounting System You can now place your sensors in the grenade. I mounted a DS 18S20 Temperature sensor on the 90-HS01K-000 Humidity sensor PC board as shown in Fig 7. This is a easy way to mount both sensors with only one wiring connection. Remove the cap from the grenade and slide the cable down the core. Let the sensor PCB sit about ½ from the top of the core. Hold in place with a blob of plumbers putty or other suitable putty. Completely plug the core around the wire to prevent insects from entering. I used some automotive putty for windshields. These are

5 suitable putties. Don t use RTV as the fumes from RTV last a long time and may contaminate the sensor, I not sure. Besides RTV is messy and it will take a lot to fill the center of the core. I mounted my grenade in the shade about 2m off the ground under the eaves of my radio shack using a ¾ PVC electrical sweep. See Figure 6. You could use any other conduit type arrangement with this design Figure 7, Addition of DS18S20 Temperature Sensor to Humidity Sensor PCB 1-Wire Dallas Semiconductor