LiPo Battery Tester For Solar Vehicle Battery Array

June 27, 2012 by Mike Szczys 12 Comments

If you’re building solar vehicles at a competitive level you’ve got to know exactly how the storage batteries will perform. To that end [Matthew] built a Lithium Polymer battery tester for use by the McMaster University Solar Car Project. It worked well, but could only test one battery at a time. He just finished up a second version, which can test battery specifications on up to eight units at once. It saves a lot of time, but still takes fifteen hours to test just one set of the units used by the vehicle.

The most important aspect being measured is the discharge curve. Sure, there’s a datasheet that includes this information, but how can be sure that what you received will perform at spec? Each of the eight channels can be disconnected from the system using a relay. This is just one of the safety features which watch for things like over-voltage and over-current conditions. Remember, Lithium batteries can heat up fast if there’s a problem. Data is sampled on a 12-bit ADC and can be pushed to a computer via USB for graphing.

Urban Farming Uses Aquaponics To Make Farmland Where There Is None

June 27, 2012 by Mike Szczys 47 Comments

[Eric Maundu] is farming in Oakland. There are no open fields in this concrete jungle, and even if there were the soil in his part of town is contaminated and not a suitable place in which to grow food. But he’s not using farming methods of old. In fact farmers of a century ago wouldn’t recognize anything he’s doing. His technique uses fish, circulated water, and gravel to grow vegetables in whatever space he can find; a farming method called aquaponics.

The video after the break gives an excellent look at his farm. The two main parts of the system are a large water trough where fish live, and a raised bed of gravel where the fish waste in the water is filtered out and composted by bacteria to becomes food for the vegetables. More parts can be added into the mix. For instance, once the water has been filtered by the stone bed it can be gravity fed into another vessel which is being used to grow lettuce suspended by floating foam board. But the water always ends up back in the fish trough where it can be reused. This ends up saving anywhere from 90-98% of the water used in normal farming.

But [Eric] is also interested in adding some automation. About seven minutes into the video we get a look at the control systems he’s working on with the help of Arduino and other hardware.

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Analog Soil Moisture Alarm

June 22, 2012 by Mike Szczys 19 Comments

The lion’s share of soil moisture monitors we see are meant as add-ons for a microcontroller. So we’re glad that [Miceuz] tipped us off about this soil moisture alarm he built with analog parts. It’s really not hard to take the concept and build it in the analog world. That’s because you’re just measuring a resistance value. But for those of us who never really got started with analog parts this is a great project to learn from.

A high-efficiency op-amp is doing the brunt of the work. When the soil is moist the resistance is rather low compared to a reference voltage provided by a separate resistive divider. But when the plant gets thirsty and the soil dries out the resistance increases, triggering the op-amp to illuminate an LED and create some noise on the buzzer (we’re a bit confused on how that buzzer works).

Unfortunately this isn’t a viable long-term solution as the battery calculations show it lasting only about four months. That’s where a microcontroller-based circuit really shines, as it can put it self in low-power sleep and wake infrequently to take readings.

Using Solar Cells To Track The Sun For Your Solar Cells (dawg)

June 19, 2012 by Mike Szczys 13 Comments

This solar panel tracks the sun using solar cells. It’s a pretty interesting technique, and can be done on the cheap.

The rectangular panels are doing the actual energy harvesting. The circular modules seen below are solar cells from some landscaping lights. They’re being used as sensors to help judge if the device is aimed directly at the sun. We’ve already seen this type of thing done with a quartet of light dependent resistors. In this case, if the negative leads for both landscaping lights are connected, a voltage may be read from the positive lead of each panel. If you measure that voltage, and use a rotating stand to adjust the position until the readings balance, you can be assured that your array is getting the optimal amount of sunlight.

[Gtoal] had been trying to drive motors directly from the output lines of these panels without success. We’re sure there’s a simple analog comparator circuit which would facilitate this. Grabbing a small microcontroller is another option (and some chips have an analog comparator built in).

Counting Bees

June 14, 2012 by Mike Szczys 20 Comments

This is the bee counter which [Hydronics] designed. It’s made to attach to the opening for a hive, and will count the number of bees entering and exiting. We’re not experienced bee keepers ourselves (in fact we’re more of the mind of getting rid of stinging beasties) but we understand their important role in agriculture and ecosystem so we’re glad someone’s making a nice home for them.

Most of the apparatus is a circuit board lined with reflective sensors. There is a double-row of pin sockets on the top of the board which accepts the Teensy+ which monitors those sensors. The bees must pass below this PCB every time they enter or leave the hive, thereby tripping a sensor. In the video after the break [Hydronics] shows off the system with a netbook used to monitor the output. But it sounds like he has plans for an integrated display system in future versions of the bee counter.

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Large-scale Arduino Controlled Greenhouse Does Some Serious Farming

June 5, 2012 by Mike Szczys 17 Comments

[Instrument Tek] isn’t messing around with a hobby-sized greenhouse. In fact if it were any bigger we’d call it a commercial operation. But what interests us is the professional-quality greenhouse automation he built around and Arduino board.

The greenhouse is about what you’d expect to see at a nursery, except the footprint is somewhere around 10’x10′. It’s a stick-built frame with walls made of poly. Professional greenhouses monitor and regulate temperature and humidity and this one does just that. The video after the break starts off by showing the controller box. It has temperature, humidity, and light sensors that allow the Arduino to judge growing conditions. If it gets too hot, some slats are opened and a fan exhausts air from the structure. If it gets to cold, a series of light fixtures are energized. They contain heat lamps, as this setup is in northern Alberta, Canada and it can get quite cold some nights. The drip system is also automated, with a solenoid to turn water on and off.

In addition to that 3:26 show-and-tell, we’ve embedded a 27-minute video that shows how to build the controller box. So you can start you plants indoors on the rack, then populate the greenhouse when they get large enough.

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Charting The Efficiencies Of Boiling Water

June 2, 2012 by Brian Benchoff 32 Comments

Water takes a lot of energy to heat up. If you’d like evidence of this, simply jump into a 50° F swimming pool on Memorial Day. Despite the difficulty of heating water, that simple act accounts for a lot of industrial processes. From cooking a steak to running a nuclear reactor, there isn’t much that doesn’t involve heating water.

[Tom Murphy], Physics prof at UCSD decided to test out exactly how efficiently he could boil water. Armed with a gas stove, electric kettle, microwave, and a neat laser pointer/photodiode setup on his gas meter to measure consumption, he calculated exactly how much energy he was using to make a cup of tea.

The final numbers from [Tom]’s experiment revealed that a gas stove – using a pot with and without a lid on large and small burners – was about 20% efficient. A gas-powered hot water heater was much better at 55% efficiency, but the microwave and electric kettle had a miserable efficiencies of around 15 and 25%, respectively. There is a reason for the terrible inefficiency of using electricity to heat water; if only the power from the wall is considered, the electric kettle put 80% of energy consumed directly into the water. Because the electricity has to come from somewhere, usually a fossil-fueled power plant that operates at around 30% efficiency, the electric kettle method of turning dinosaurs into hot water is only about 25% efficient.

The take-home from this is there’s a lot of power being wasted every time you run a bath, make some coffee, or wash the dishes. We would all do better by decreasing how much energy we use, much like [Tom]’s efforts in using 5 times less power than his neighbor. Awesome job, [Tom].