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No articles for week of September 02, 2015

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August 20, 2015

The Sun Dragon Tracks Current

Fully Self-Monitoring Sun-Dragon

Fully Self-Monitoring Sun-Dragon

So current tracking on the Sun Dragon has been a major problem. It started when I kept blowing up high end operational amplifiers. They would work fine on the breadboard, but fry when I moved the setup to the Sun Dragon. I decided I was tired of the op amps and moved to using a 16-bit serial A/D. Again, this setup worked great on the test system but burned the chips up instantly when they were moved to the Sun Dragon. After some investigation and many replaced parts I made the discovery I didn't like. The charger system uses a common positive and several different grounds. By trying to measure the current I was connecting these grounds together and causing all my problems.

Aside from getting rid of the charger that I don't like, the only way around this problem is to use isolation. So, I ordered an isolated power supply and a synchronous serial bus isolator. My initial order was messed up as I ordered the wrong part. It was an isolator, but designed to be used with several other parts to do the isolation—not what I wanted. The correct parts arrived yesterday and I went about getting them setup.

The basics are simple. I have a microcontroller that talks to some 16-bit A/D chips using an SPI bus. To isolate the A/D chips that are doing the measurements, I need to connect them to an isolated power supply. And to communicate to these chips, I need to go through an SPI isolator.

The isolated power supply is connected to my normal 5 volt power supply, and generates a 5 volt supply for the A/D. Internally there is a high-speed oscillator that turns the 5 volts DC into AC. This goes through a transformer, which isolates the ground, and then converter back to DC. Both the isolated and non-isolated supplies go into the SPI isolator. This device is a high-speed bi-directional optocoupler—light is a pretty good electrical isolator.

My initial attempts to get the system working did not accomplish much. So I set the project down for the night and tried it again the following day. I had an idea, which turned out to be the problem. The isolated side of the SPI bus did not have pull-up resisters on the signals. Normally SPI signals are pull up, and whatever is talking will pull the signal down. This is generally done at the SPI master source. But the isolator keeps the source separated from the rest of the bus. Once I added some 10k pull up resisters, my SPI communications was working just like it should. I let the setup run overnight.

This morning it was time to integrate the isolated setup with the Sun Dragon. This is usually where stuff blows up. This time, however, everything worked as expected. The isolated A/D kept the grounds from being connected and now the Sun Dragon can manage its own current readings. That is a major hurdle for the project—long overdue but now functional.

The only part of the project that remains is the backup power relay. So far this summer I haven't needed to use any backup power, and the Sun Dragon has run for 96 days completely on solar power. However I don't expect that will be the case come winter when days are short and often overcast. I decided to change how this works as well. Rather than simply switch to a separate voltage source, I decided it would be best to also switch on the AC to that voltage source. Wall warts are notoriously inefficient, even when nothing is connected to them. So the ability to leave it without power until it is actually needed would be for the best.

   Last night I did my standard airport-Ashton run, and made the loop in a record 47 minutes, 55 seconds.  Because I started in the evening, I had no traffic and almost no wind.  On the 12.2 mile trip I averaged 15.28 MPH, had an average heart rate of 159 BPM (86.9% of my maximum) and a maximum heart rate of 172 BPM (94.0% of my max).  This was the my first ride after taking it easy for a couple of days of recovery from Delayed Onset Muscle Soreness (DOMS).  While I didn't get my heart rate as high as I would have liked I nonetheless did a record setting run.
   Today I did it again.  I had two stop lights, a stop to remove an outer shirt, and strong winds from the south-west.  This trip took me 50 minutes, 14 seconds for an average speed of 14.56 MPH.  However, my average heart rate was 161 BPM (88% of max) and my maximum was 175 BPM (95.6% of max).  I've turned a 50 minute bike ride with a hill climb into a sprint.

August 17, 2015

Operation Lux One Year Results

Operation Lux has been running over one year on the roof of Elmwood Park taking measurements minute by minute of sunlight intensity. Now that I have a complete years worth of data (less some downtime from last September) I decided to analyze it.

Object1

Here are the most important results from the operation—the average amount of light received during a day for each of the months throughout the year. The thick black trace is the yearly average, but as the chart shows each individual month can differ significantly.

Shown are monthly averages of light for the entire year. Clearly visible are the effects of the sun's declination with daylight beginning shortly before 6:00 am and lasting until after 8:00 pm in the summer months, but not until after 8:00 am and only until 5:30 pm in the winter.

Object2

Here we see the average amount of light in a 24 hour period for each in watt hours per square meter. Notice how much less light hits the roof in January, December and November than the rest of the year. Factors include the angle of the sun, the tree line around our house, cloud cover, and snow.

So in the summer months I see no problems having my 50 watt solar panel power the web server. But for a couple of the winter months there may not be enough light to keep the server battery from running low. This is why I have designed the Sun Dragon with a relay to switch itself to auxiliary power. This will allow the battery to recharge from solar power for however long is needed. Thus the Sun Dragon may not be 100% solar powered all the time, but it should be close.

During the summer months there is much more power available than the server needs. I have been thinking about what can be done about this. One option is to have the server contribute to some distributed computing projects such as Einstein@Home when there is excess power available. Because of the quantity of power, I may have to add a couple of additional computers to fully utilize this power. This is only a concept right now.

   Went on a run in the morning with Zach despite the heat and humidity.  Zach can run more than 4 miles, but I don't think that is something I am going to be able to do for sometime.  So we just ran a single mile.  I did the mile in 8 minutes, 13 seconds with an average heart rate of 169 bpm (92% max) and a peak of 184 bpm (101% max).  The peak was at the end where I ran as fast as I could still move for about 1/2 a block.  While I don't really enjoy running, I do like how much it makes me work.  So this is something I might have to look into doing more often.
   The other day at coffee it started raining with the sun out, so I took a picture.
   Last night I decided to go for an all-out run on my standard Airport-Ashton loop bike ride.  The goal was to push hard and get a baseline for heart rate for what I would consider vigorous exercise.  This is a 12.4 mile loop with one large hill climb.  Winds were from the west and pretty steady, which means I had a strong headwind on the first part of the trip.  The results: loop completed in 50 minutes, 24 seconds with an average heart rate of 163 beats/minute (89% of max) and a maximum of 177 beats/minute (98% of max).  I kept my heart rate under the recommended maximum for my age, 183 bpm and it is estimated I burned 730 calories with this single ride.  My average speed was 14.76 mph which I think is among the highest in my records.
   Today I am feeling the consequences of this ride.  To me, that is a good thing.  I hardly get Delayed Onset Muscle Soreness (DOMS) which means I'm not really pushing my mussels that hard.  When it does happen, it means I was really making my leg mussels work.  So today I did a very similar loop, but made it a 15 mile ride with a 1.33 mile hike.  Taking it very easy, including a granny gear ride up Hell Hill I averaged a heart rate of 142 bpm (78% max) with a maximum of 165 (90% max).  According to the Mayo Clinic, these levels still qualify as vigorous exercise intensity (70-85% of max).  According to this page, my slow ride places me in The Target Heart Rate Zone which is "is an area of moderate intensity activity that leads to improvements in your aerobic capacity and burns fat.  This zone provides many benefits for all fitness levels, including those who want to lose weight, those who are training for an athletic event, or those who are looking to have more energy and get fit."  My 89% qualifies as The High Intensity/Anaerobic Zone which says it is "recommended for highly fit individuals, such as athletes.  This zone places a high demand on the cardiovascular system and does not burn much fat."  I'll take being being in a category of highly fit individuals.
   Pictured is Steve and Zach out with me exploring a coffee shop we had not yet been.
   My last day of work today before my leave of absence.  After today I switch to school.  Work has been keeping me busy, and so I have two weeks to find a place in Platteville to live for the next 9 months in addition to all the other preparatory items to get ready to be a student again.  But my company is pretty cool.  While they don't want me to go (they have work that needs to be done) they are working with me so I can continue to work on my degree.
   Here are the remaining battery banks on the electric Studebaker truck.
  A work project (that didn't involve me) where they converted a Studebaker truck to be an all electric vehicle.  It is very quiet with the tires and frame vibrations making more noise than anything else.  Pictured is the engine compartment with one of the banks of batteries.