We bought some Serial LED strips for the shop and I am having a whole lot of fun programing them. Like most 12 volt strips they are wired with three LEDs in series, which are in turn controlled by one high-speed serial chip. So there are 50 control chips on a 5 meter strip. (The strips have 30 LEDs per meter). We looked for strips with 60 LEDs per meter but our supplier could not provide them without a sizable order from the factory.

The somewhat coarse grain of this control might be a show-stopper for some LED projects, but they’re well positioned for lots of general computer-controlled changeable color and display applications. I am having a whole lot of fun programming them. I found an excellent high-speed library here. The author hasn’t returned my email yet, I’ll call him Daniel G. from his email address, and give him more specific credit if I can get in touch, and he wants the attention.

Our LED strips are controlled with the UCS1903 chipset, which has, as one of its great virtues, the ability to control the LEDs with only a ground and data line. All of the Chip Select and Clock functions have been replaced in the chip, by careful timing control, which also requires a microController running at least 16 Mhz, so Lillypad owners are out of the picture, at least for now. The lack of clock signal lines creates a very clean interface. Two wires, Ground and +12 volts, go to the strips from the power supply, and two wires, GND and Data In, connect the microcontroller to the strips. The strip headers thoughtfully have two wires on ground (if you buy a whole 5 meter roll), so it’s a very easy hoookup. More strips can just have data and GND lines daisy chained, and power lines perhaps run in parallel, to avoid huge currents through the strips, although it might be possible to run 10 meters daisy chaining all four wires, especially if all the LEDs are not on at any one time.

Writing 255, 255, 255 to all LEDs yields a strip (5 meter) operating current of 2.3A (@ 12 volts). The total current divided by 150 (50 controller chips x 3 colors) yields about 15mA per LED so the strips should have a long lifetime at that current, since most superbright LEDs are usually rated at 20 mA or greater.

I cooked up five demo sketches to help users get going on using the library. There are some videos below (of uneven quality) showing the effects. There are some nasty flickers in some of them that just represent interference patterns between the video frequency and the update frequency of the LED’s. Needless to say, the LEDs don’t look like this to the human eye. Cyborgs though, will eventually be connoisseurs of visual phenomenon entirely invisible to people.

The Serial LED strips are in stock and in the shop here.

Paul picked these servos up for his class, and liked them so much that we are now putting them in stock!

This is a standard analog hobby servo with nylon gears. It also features 2 ball bearings on the main output shaft. Ball bearings are rare on inexpensive “generic” servos, so this is definitely a nice feature to see.

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The world probably has enough ATMega32u4 (Arduino Leonardo) development boards. Some of them even put all the pins on a .100″ grid (unlike the original Arduino outline). But we feel that none of them is as easy to use on a breadboard as the BBLeo, which stands for breadboard Leonardo. The BBLeo is engineered to get you going quickly on a breadboard.

Just as in the Arduino Leonardo, the BBLeo has USB built in so you can just “plug and play”. Hint – all this great functionality that board developers like to brag about is usually built into the chips. We try to be honest about it.

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There are a number of ways to sense electrical current — and all of them involve some fuss, at least in comparison to sensing voltages. The chief reason for this is that because current is a flow, rather than a potential (like voltage) we need to measure it in series with the circuit, rather than in parallel.

For beginners, this is the reason that your multimeter behaves so much differently when you switch it into the current ranges. The resistance of the meter is now very low, as it is meant to be inserted in series with a circuit. Consequently if you inadvertently touch a voltage source with the probes, it is like applying a short circuit to the voltage, and the protective fuse in the meter blows out, something that is easy to do by the way, and that I’ve done at least once with all of my meters.

Another popular way of sensing current, is to insert a low value resistor in series with a circuit and measure the voltage drop across the resistor. This is convenient when using small DC circuits, less so when using mains circuits (120 volts or 240 in Europe). By the way, this is the way your meter senses current, and the fuse is protecting the low-value resistor, which would otherwise be liable to a smokey death in inadvertent current-measuring mistakes.

When using mains circuits, often a transformer is employed. Even the electrician’s clamp meters work this way – although the principle may not that be clear. Only one conductor is inserted in the clamp meter, which acts as a one-turn primary and the meter forms the secondary winding of the transformer. Note that if both conductors are inserted into the clamp – say a lamp cord, that no reading is possible, because the two wires have equal but opposite fields, which promptly cancel each other.

Many other small current transformers are available, but for the hobbyist, the problem of tying the circuit to the mains, then finding an enclosure to house the transformer, is also some fuss. Lately hall effect current-measuring chips have become available, for measuring current, but the fuss is still in connecting them to the circuit and housing them.

Wouldn’t it be nice if you could measure current without having to mess with cords or plugs at all? There are small hall effect sensors with linear output that can be used to measure magnetic fields. I thought that it might be possible to use these to measure the current in common electrical wires such as lamp cords. You might be quite right to wonder about the equal but opposite fields from the lamp cord’s other conductor. The trick I have used is to get the sensor physically closer to one wire than to the conductor.

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