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Kyle

Kyle

   Today was the celebration of Star's graduation of UW Whitewater.  Caught up with Star, Tazz, Kyle (pictured), Erica, and several other people from U-Rock.  Tomorrow will begin my next big road trip, so updates will not be again until I return in a couple weeks time.
Lisa and Que

Lisa and Que

   Met up with Lisa after work and tried a Laosasian restaurant for dinner, followed by a bike ride around Lake Monona.  On the ride we ended up in an area I plan to incorporate into my ride to work that will keep me off the busy street of Broadway.
Noah

Noah

   Coffee with Noah and Mary this evening.  Noah and I have been exchanging stories about our Arduino projects.  He has a great interest in battery charging technology and we discussed my solar power web server project with my desire to design an Arduino controlled charger to replace the existing charger.
   In the past 5 months I spent a bunch of time on the bench at work waiting for projects to need software.  This week, despite missing Monday, will be a 40 hour week as it seems everything needs to be completed at once.
   Tonight at swimming I decided to count my endurance laps.  At the end of the night I swim two sets, each for 10 minutes.  The first set I use swimming fins and work on my legs.  The second set I do a front crawl with no legs to work on my arms.  I decided to count the number of laps I did for the 10 minute leg portion, and it came to exactly 28, or 700 yards.  My goal is to do 700 yards in 12 minutes, but without fins.  So this is a good indication I am on the right track.  It also means I averaged a 25 yard lap every 11.67 seconds.  Doing the math, this comes to an average swimming speed of 2.39 MPH (3.84 km/h). 
Azorius

Azorius

   Today some LED lights arrived and I worked them into Azorius' terrarium.  They are battery powered LEDs that use very thin wires, and I think they work quite well for illuminating the dragon's habitat.  I plan to replace the battery packs with a wired power from a phone charger source.
   Much of the weekend has been rainy, but the Memorial Day holiday had a break in and I decided to go for a bike ride.  I did just over 10 miles.  The goal was to have a look at Middleton Hills Neighborhood Park South.  It consists of a marshy area with some islands in the middle.  It has a walking path, but not a bike path on the islands, so I didn't traverse them myself.  I continued on through the Middleton Hills Neighborhood and then through the Pheasant Branch Creek Conservancy.  As I was exiting the conservancy I decided my ride had not been long enough and traveled up county road Q, and along Balzer Road which I had not been on before. I was traveling west and the strong headwind kept my speed about 10 MPH despite going down hill.  Along Pheasant Branch road I took the quintessential Wisconsin picture shown here.

May 24, 2015

Manual Current Measurements

   While I don't have the ability to connect the current measurement directly to the Sun Dragon, I can have them connected to an Arduino and fed back to a PC.  This way, I can use a terminal program to log the data and get some current information.  Today I this up.  The setup is fairly simple and what I had the first time around.  While the data won't be time stamped, I can still get an idea of the charging characteristics of the battery and the currents generated by the setup.
New Belt Needed

New Belt Needed

   As the weather becomes warmer, I am wearing less layers.  I am now down to a single shirt, and I've noticed my pants just are not staying up with the tightest setting on my belt.  So, I drilled 3 new holes in it.  Seems the new tightest setting is nice and snug, and should keep my pants from wanting to fall off.
   Pictured is my belt pulled such that it isn't too tight.  It clearly demonstrates the need to for more holes.  I have warn size 32x32 pants for at least 10 years, likely longer.  My guess is my waistline is now somewhere between 30 and 28 inches.  I think I recall buying 28" pants right after high school.  My weight has been pretty steady the past month, and it is likely this is the skinniest I have been in 19 years.

Until I can switch out the battery charger on my solar setup, I have to deal with the strange grounding problems it produces for measuring current. Since I was able to measure all three currents with a computer isolated from the charger, it is clear isolation is the key. There is a way I can do this with my existing setup. It requires an isolated power supply, and optical isolators for digital signals. The power supply doesn't need to be big—just needs to drive three A/D converters. And I only need two digital signals for the I2C bus. These signals can run at over 400 kHz, so my optoisolator needs to be fast. Luckily, they make such devices—and make them in through-hole packages. I found a cheap isolated power supply, and some 2 channel, 10 MHz optoisolators. In a couple weeks, I should be able to test them out.

May 21, 2015

Experiments with Digital Potentiometers

I tried an experiment with some digital potentiometers that unfortunately ended in failure. I have a buck converter with two potentiometers: one for setting output voltage, and the other for setting a current limit. I removed one of the potentiometers and wired in a digital potentiometer. In theory I should be able to control the voltage from an Arduino. The digital pot takes a simple command from an SPI bus to select resistance, and each device consists of two potentiometers.

Initially things seemed to be going well. The digital pot was easy to wire in, and easy to control with the SPI bus. But I was never able to set the buck converter to anything higher than 6.5 VDC no matter how much/little resistance I set. I could go from 0 to 6.5, but everything stopped after this point.

I tried several things, none of which had an effect. The following day at work I asked an electrical engineer what might be the problem. They pointed out something I had overlooked. Digital potentiometers have some kind of analog switch internally in order to switch resistance. Those switches have a maximum voltage—VCC plus a little extra. Over this voltage, they would not work correctly and the resistance skewed. A quick look at the data sheet and this was clearly my issue. At 5 volts, this device could not handle the input voltages. My converter could have voltages up to 20 volts. They do make a digital pot that can use voltages in this range. Should I continue this route, I may have to pick one up.