Air Quality Sensor

An air quality sensor (dust sensor) has been on my todo list for a while. There are a number of sensor modules on the market for the DIYer but all that I had seen seemed to not be suited for outdoor use. I saw someone that had a PurpleAir sensor. The specs looked good but it was quite expensive and had to be connected to their cloud network. Looking into it more I found that the actual sensor in the PurpleAir device was a Plantower PMS5003. This sensor is available online for around $40. That is more my speed.

My standard interface for sensors is to use a Teensy 3.2 microcontroller to convert whatever signals the sensor uses into USB serial. The PMS5003 interfaces with 3.3V logic level serial data and a set and reset line. The Teensy turns on the sensor every 5 minutes waits for 30 seconds for the fan to come up to speed takes readings and turns it back off.

 The Teensy is mounted on a piece of perfboard along with the connector for the sensor.  The perfboard is mounted to an aluminum disk that just fits inside a PVC pipe cap.

The sensor is mounted to the other side of the aluminum disk.

The PMS5003 does need to be protected from the elements when used outdoors. In the pictures of the PurpleAir sensor it looks like it is mounted in a PVC pipe cap with the open end facing down. So I went out and bought a 4 inch PVC pipe cap and added an aluminum bar to mount it.

Above on the right is the sensor mounted on my weather station tower along with a number of other sensors.

A USB cable connects the sensor with a computer in the base of the tower. This computer runs a script that sends the data every five minutes to my web server where it is logged in a MySQL database. You can view the plots of the data at the link below.

References:

Sensor Data http://www.ocrslc.net/sensors/dust.php

 

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Telescope Mount Adapter

The University of Iowa donated the Rigel robotic telescope to the Cedar Amateur Astronomers. Plans are to install this telescope in one of the domes at the observatory. To mount the scope an adapter is needed to connect the scope to the concrete pier in the dome and to raise it to the proper height.

Dr. Scott Bounds designed an adaptor and worked with the University of Iowa Physics Department Machine shop to get it fabricated. The adaptor is made of donated aluminum plate. The bottom plate is 1.75″ thick and the rest of the parts are 5/8″ plate.

Dr. Bounds has been busy with his work at the University and Fred Young and myself wondered if we could help out getting the adapter completed. When we inquired about it we were told that it was complete except for the welding. So I offered to help with the welding. My son Paul does aluminum welding and our recently acquired welded is capable of aluminum welding. The machine shop foreman delivered the adapter parts to my shop. It was then that I learned that they had tried to weld the adapter but were unable to get good welds. This made me a bit nervous. We were thinking that they just did not have the time to do the welding.  They were trying to use a TIG welder. TIG welding is excellent for precision welding but is not really suited for the heavy duty welding needed for this thick material. We have a MIG (wire welder) which is more suited for this type of welding. Our welder is set up for .035″ wire.

Above is the mount as I received it.

To clean up the poor welds I used an angle grinder to remove the welds and disassemble the pieces. I ground off all the old weld so we could start over with clean parts. Essential for good aluminum welds is clean metal. After the parts were ground clean they were wiped down with acetone to remove any potential grease or oil.

We did not know what alloy the parts were made of so I just picked one of the two common welding wire types (4043) and turned the welder up to a fairly high power level.

Due to the thickness of the part we thought the preheating would be necessary. So I arranged to preheat the parts with a fish fry burner.

After making a few welds we noticed that the welds all had a crack running the length of the weld. Clearly something was wrong. The dull look of the welds also indicates gas porosity in the weld.  We finally decided that we were welding too hot. The welds were all ground out to get ready for the next attempt. Along with turning down the power we switched to the other common welding wire (5356) and skipped the preheat.

The changed did the trick and we had a nice shiny weld with no cracks.

Above is the adapter with the bottom welding complete and the top plate clamped on to tack weld in place before flipping the adapter over to weld on the top plate. The welding used 4 pounds of welding wire and about 100 cubic feet of argon.

Above is Paul welding on the adapter.

After the welding was complete I sandblasted the adapter to remove the weld smut and splatter. After a coat of paint it will be ready to return to the University shop for final machining.

References:

Cedar Amateur Astronomers https://www.cedar-astronomers.org/

A short video of Paul welding on the mount. https://youtu.be/0kKoOcM15zw

 

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Biochar Study

This is a  citizen science activity that I spotted on Scistarter. I keep an eye on the citizen science projects on Scistarter and this one interested me. Scistarter lists a lot of citizen science projects.

I had seen a lot of things on the internet about using biochar as a soil amendment but did not pay much attention. When I found this project I did a little more reading about biochar.  Biochar is a fancy name for charcoal. I found that there is a lot of research going on studying various aspects of biochar. From what I can see the main benefit of biochar is carbon sequestering with the added benefit of improving the soil for plant growth.

This project is studying the aging of biochar in the soil under a wide variety of conditions. One way to do this is to get citizen scientists from different areas to bury samples of the biochar. The USDA is doing the research for this project. See link references below for more information on biochar.

After I signed up for the project I received a box with four mesh bags of biochar and instructions for burying them. The bags contain some oak biochar and a temperature data logger. One piece of the biochar was sealed in a plastic bag as a reference. The bags were labeled B07 through B10.

The bags were buried on April 18 2019.

I picked four sites around my place to bury the bags. I tried to pick sites that were as different as possible.

 

Above is my trailer loaded with the things I needed to bury the bags. Some metal fence posts were used to mark the burial sites.

Above is a Google Earth image with the location of each bag marked.

 

Above is bag B07 in the hole. This site is at 42° 11.955’N 91° 39.256’W. It is under some very large Tartan Honeysuckle. That honeysuckle is very invasive and I really need to get rid of it. The soil here is quite sandy.

Above is a view of the site for bag B07.

Above is bag B08 in the hole. This site is at 42° 11.934’N 91° 39.310’W. This is an area that stays wet a lot of the time. It is a grassy area that I am trying to get native prairie flowers growing. It will not get mowed this year. I burned off the general area here this spring but this exact spot did not burn because it was too wet.

Above is a view of the site for bag B08. You can see that it is a wet low spot.

Above is bag B09 in the hole. This site is at 42° 11.834’N 91° 39.310’W. This area used to be a horse paddock. I planted some trees here some years ago. A lot of the pine trees I planted died. The hole is next to the stump of one of the pine trees.

Above is a view of the site for bag B09.

Above is bag B10 in the hole. This site is a 42° 11.915’N 91° 39.313’W. This is near my garden and next to my asparagus and rhubarb patch. A lot of stinging nettle growing here also.

Above is a view of the site for bag B10.

In six months the bags will be dug up and sent back to the researcher along with soil samples from the sites.

October 10 2019

The bags were dug up today.

 

 

References:

Scistarter https://www.scistarter.org/biochar-soil-aging

USDA ARS https://www.ars.usda.gov/midwest-area/stpaul/swmr/people/kurt-spokas/biochar/

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Soil Temperature Probe

A soil temperature probe has been on my todo list for a while. So I decided to build one now along with a number of other improvements, and repairs to my weather station.

The soil temperature at four inch depth is what is used for agriculture and I added sensors at 1,2 and 3 feet. The deeper sensors are mainly for my own curiosity to see annual variations in soil temperature.

The sensors are Microchip MCP9808 Silicon Temperature Sensors mounted on a little board by Adafruit. These sensors communicate via I²C so they can be all wired in parallel and addressed by a microcontroller. To protect the sensors in the ground they are inside a length of 1/2″ PVC water pipe.

Above is a picture of the sensor string and the length of pipe they will go in. It takes four wires the connect the sensors and some telephone wire is a handy way to connect them along with a RJ11 telephone connector on the end of the wire.

Above is a picture of the completed probe. The sensors are in the longest length of pipe. Then a one foot section  gets the sensors away from the place where the probe comes to the surface. This is to prevent the probe or the opening in the ground caused by the probe from affecting the temperature at the sensor. Another length gets the probe above ground. It also allows the probe to come out of the ground next to a leg of my weather station reducing the chance of damage to the probe from mowing or walking on it. Then a U shaped section gets the opening for the wire pointed down. The wire is sealed with silicone but I wanted to also have it pointed down to prevent rain from pooling on the seal and possibly leaking. I filled the pipe with dry sand to prevent convection currents of the air inside the probe from affecting the sensors.

Here is the probe buried next to my weather tower. Because of the horizontal section of the probe the sensors are over a foot from the tower leg. That should be enough to prevent the leg from affecting the readings.

The probe is connected to a Teensy 3.2 microcontroller. I designed and had made a carrier board for the Teensy it just holds the Teensy and connects it to the RJ11 connector to the probe. In previous projects I mounted the microcontroller on a piece of perf board and hand wired the connections. This is much neater and more reliable. The board is sitting in a plastic case to protect it.

The Teensy reads the data from each of the sensors via the I²C bus. The data is then sent over the USB to a Linux machine (Beaglebone Black) which receives data from all the weather tower sensors and send the data to the MYSQL server on the web.

 

This is a plot of the first  4 days of logging. Red is the 4″ sensor, Blue is the 12″ sensor, green is the 24″ sensor and black is the 36″ sensor. It was warm the first day then it cooled off. The order of the plots completely reversed. As the ambient air started cooling the soil rather than heating it. The smooth lines in the middle of the plot are where I lost some data while switching web servers. The ripples are probably due to sampling noise in the sensors.  I will add some averaging of he samples to smooth out the plots. I also need to fix the time and date labels to make them more readable.

The soil temperature data is online at: http://www.ocrslc.net/sensors/soiltemp.php

References:

Adafruit https://www.adafruit.com/

Teensy from PJRC https://www.pjrc.com/

Beaglebone black https://beagleboard.org/black

Carrier board made by Seeedstudio Fusion https://www.seeedstudio.com/

My web site http://www.ocrslc.net/

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Rain Sensor

I thought it would be interesting to add a rain sensor to my tipping bucket rain gauge. Because it take time for the bucket to fill and does not always tip right when it stops raining a sensor that detects rain would help tell more precisely when the rain starts and stops.

The Hydreon RG-11 rain sensor looked like it would work well for this application. This sensor is rugged and not too expensive. It works on the same principle as automatic  windshield wipers. The rain drops on the clear plastic reduce the internal reflection of light. It can be set to just detect rain or measure rain fall. Although it is not terribly accurate at measuring the amount or rain fall. I set it to just detect rain.  The sensor runs on 12 volts and outputs a contact closure when it detects rain.

The RG-11 sensor is the dome to the right in the picture.

I already have a tipping bucket rain gauge connected to the Internet so it was fairly simple to add the RG-11 to the setup. The sensor was connected to an input on the SparkFun ESP8266 DEV and the software modified to read the input and report it to my web server.  I also had to modify the web software to log the readings to the SQL server and add the information to the plot on the web page. See my IoT rain gauge article for more information.

Just the day after I installed the rain sensor it rained on the last day of December. The tipping bucket data is the blue line on the plot and the green areas are when the sensor is indicating rain. In the plot above the green line around 8:00 is when I manually activated the sensor to test it. Around 16:00 the precipitation gradually changed to snow. The sensor does not detect snow.

 

 

References:

http://rainsensors.com/ Hydreon RG-11 rain sensor

https://jimhannon.wordpress.com/2018/02/02/iot-rain-gauge/ My tipping bucket rain gauge installation.

http://www.ocrslc.net/sensors/rain.php The sensor online.

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Barn Door Star Tracker

I wanted to take some star pictures with my DSLR and decided a barn door style star tracker would be a fun project to build.

Early versions were nothing more than two boards connected by a hinge with a screw to adjust the angle between the board. One board was attached to a tripod and the other board held the camera. By periodically turning the screw a small amount the camera could be made to follow the stars. Manual adjustment could be eliminated by  using a 1 RPM motor to turn the screw. Using a straight screw leads to errors in the tracking angle for longer exposures. The Trott double arm drive was one effort to reduce the tracking error. The use of a curved screw eliminates the tracking error but requires the nut be turned rather than the screw. I chose to use the curved screw turned by a stepper motor. This way I can adjust the tracking speed in software and reset the tracker with a push of a button.

My design is a bit more sophisticated than two boards but still much less expensive than commercial camera trackers I have seen. I chose to make it out of metal.

Above is the bottom plate that attached to the tripod. It has a 1/4-20 hole in the middle for the tripod screw. Mounted on this plate is a microswitch assembly used in 3D printers. The switch signals the microcontroller when the drive is back to home position.

Above is the top plate that holds the camera. Also on this plate is a dovetail mount for a finder scope used to align the tracker with Polaris. These plates are 1/8″ thick and 3 by 12 inches.

Above is the stepper drive assembly. A stepper motor drives a timing belt pully which hold the brass nut. A ball bearing in the other side of the pully and a hub attach the pully to the plate.

Above is the curved screw. To curve the screw I bent a piece of all thread around a curved surface and matched it to a line drawn to the correct radius on a piece of cardboard. The nuts on the end attach the rod to the top plate. This rod is longer than I expect to need. I just used the full 12 inch piece I bought.

Above is the electronics assembly for the tracker. On the perf board is a Teensy 3.2 microcontroller by PJRC a Pololu stepper motor driver and a Pololu 5V switching regulator. Power from a 12 volt battery connects to the barrel connector and two pushbutton switches control the operation. I don’t have the buttons labeled yet. One is the track button and the other is the home button. Pushing the track button will start the unit tracking. Pushing it again will stop tracking. The same for the home button except homing will also stop when the limit switch is activated. The Teensy can be programmed with the Arduino IDE. I put a hole in the case to allow a USB cable to be plugged into the Teensy for changing the software and possibly controlling the tracker by USB.

Above is the completed tracker. The curved screw sticks out of a hole in the box. I added a wedge with a 42° angle for my latitude to allow the tripod head to stay mostly horizontal. A right angle finder scope help align the tracker. A ball tripod head lets me point the camera in most any direction. If the finder scope is in the way it can be easily removed after alignment.

Above is the tracker with a camera mounted. I got a F1.8  50mm fixed focal length lens for the camera. This is a way faster lens that the lens that came with the camera. Next is to try it out. I had to take this picture with my phone as my camera only camera was on the tracker.

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Building A Sand Muller

To do sand casting a muller is almost a necessity. It is difficult to mix up foundry sand either green sand or oil bonded sand without a muller. I have been thinking about how to build a muller for some time and recently I started to build one. Basically a muller mixes and squeezes the sand a binder to get a uniform mixture with the binder coating the sand.

The basic design I chose uses a rotating cylinder with a plow and heavy cast iron wheels for mixing and squeezing fixed to a bar above the cylinder.  A transaxle from a garden tractor is used to reduce the speed of an electric motor and turn the cylinder. Besides the transaxle the cylinder is supported by four casters mounted to a frame under the cylinder.

I made a sketch using Fusion 360 to determine the size of the frame based on a drum diameter of 18 inches. I wanted the frame to be as small as possible but be able to mount  the drum support rollers on top of the frame on each side.

The first thing to build was the cylinder. It consists of a 18 inch diameter 1/4 inch thick steel plate and a 6 inch wide strip of 12 gauge steel. I had the disk plasma cut by the steel supplier and I should have had the strip rolled into a ring. Bending and wrapping the strip around the disk was a bit fiddly. I clamped the disk to my welding table and used a ratchet strap to tighten the strip around the disk.

The ratchet strap and the tack welding on the inside tended to make the rim lean inward. To fix this I used the jack to push it open before I welded the side seam.

The frame is build out of 1.5 inch square tubing. It took almost all of a 24 foot stick of tubing to build the frame. 

Here is the frame with the garden tractor transaxle installed for a test fit. The bottom of the legs have plates welded on that are tapped for casters so that I can easily roll the muller around the shop. The frame did not come out exactly square so it would rock when sitting on a flat floor. I fixed that by putting a washer on top of two of the casters. The two longer legs will support a crossbar on top of the muller that holds the roller and plows.

The pully that came with the transaxle was going to give a drum RPM that was higher than I wanted. This larger pully has been laying around and would give a suitable RPM. Problem is the original pully was attached with a special spline so I cut the hub with the spline out of the original pully trued it up in the lathe and welded it into the bigger pully.

The final part of the construction was building the plows and roller assembly. It took a bit of experimenting to get it right. One plow pushes the sand away from the center of the drum and the other plow pushes the sand away from the outside. This piles the sand right in the path of the roller. The roller is made of 4 five pound barbell weights glued together. After experimenting with this I may add two more weights to cover more of the sand with each revolution.

Above is the completed muller. It was necessary to clamp the bottom axle so that the drum would turn.

The first thing I tried with the muller was reconditioning some oil bonded sand. This worked well until the sand got well mixed. Then the oil bonded sand got sticky and built up on the roller until the roller stalled. At this point the sand was mulled well enough so it was not too big of a problem.

One of the reasons for building the muller was to be able to make and use water bonded sand (green sand). So I made a few batches of green sand. The bentonite clay that I used is oil adsorbent which is fairly larger granules. I probably could have just dumped it in with the sand and mulled away but I thought it would work better if I ground up the bentonite first. The muller did a good job of grinding up the clay and after about 30 minutes in the muller it was most a fine powder. To make the green sand I added the bentonite and fine silica sand to the muller in the correct proportions and let it run dry for a bit to mix it well. Then water was added in small amounts until the correct consistency was obtained.

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