On February 25, 1991, during the eve of the of an Iraqi invasion of Saudi Arabia, a Scud missile fired from Iraqi positions hit a US Army barracks in Dhahran, Saudi Arabia. A defense was available – Patriot missiles had intercepted Iraqi Scuds earlier in the year, but not on this day.
The computer controlling the Patriot missile in Dhahran had been operating for over 100 hours when it was launched. The internal clock of this computer was multiplied by 1/10th, and then shoved into a 24-bit register. The binary representation of 1/10th is non-terminating, and after chopping this down to 24 bits, a small error was introduced. This error increased slightly every second, and after 100 hours, the system clock of the Patriot missile system was 0.34 seconds off.
A Scud missile travels at about 1,600 meters per second. In one third of a second, it travels half a kilometer, and well outside the “range gate” that the Patriot tracked. On February 25, 1991, a Patriot missile would fail to intercept a Scud launched at a US Army barracks, killing 28 and wounding 100 others. It was the first time a floating point error had killed a person, and it certainly won’t be the last.
Continue reading “An Improvement to Floating Point Numbers”
The coffee maker which [Donald Papp] uses every morning has a water reservoir on the back that can last for several days. This means he forgets to check it and from time to time will return to find that nothing has brewed. He decided to add a low-water indicator to the machine. His approach is about as simple as it gets and we admire that accomplishment.
If it were our project we’d probably try to complicate it in one way or another. The use of a microcontroller and ultrasonic rangefinder (like this tank level indicator from a February links post) would be overkill. No, [Donald] boiled down the electronics to a homemade switch, a blinking LED, and a battery. The switch is a flexible piece of metal attached to a plastic cap using some monofilament. The cap goes in the reservoir and floats until the water gets too low, it then pulls on that metal, completing a circuit between the battery and the LED. That’s it, problem solved.
Now he just needs to plumb the coffee maker into a water line and he’ll really be set.
It has been a hot hot summer for many parts of the US. The heat has been dangerous at times and making sure the livestock has the water they need is incredibly important. [Maddox] recently upgraded the automation on their water troughs which will help with the process. Sure, they still have to check on the animals, but this will ensure there’s plenty to drink in between those visits, and that a malfunction doesn’t waste precious water.
There has always been some level of automation here, but it relied on float valves which were frequently malfunctioning. This project seeks to get rid of the float value and use solenoid valves like those used in irrigation. These solenoids can run from a 9V battery and offer quite a bit more reliability than the mechanical vales. There is still a float sensor which measures the water level, filling up the trough when needed.
An MSP430 Launchpad was used for the prototype, from which a PCB was designed. Since this needs to be weather-proof a water tight enclosure was sourced. The company that makes the enclosure also provides DXF templates which [Maddox] used to establish the size and outline of the PCB.
This Lego watercraft uses drinking bottles as pontoons arranged in a pattern that make it look very much like a Water Strider, the insects that dance on the surface of a lake.
After the break you can see a video of the rig gracefully navigating a local pond, along with a raft of ducks. It’s quiet enough not to startle them, which is nice. We don’t get a good look at the propulsion system, but [Vimal Patel] calls the floats “hockey bottles” in his Flickr comments. They appear to be Lego themed and we’re wondering if they are some type of packaging for a small set that doubles as a sports drinking bottle once the pieces are removed? The rig includes a camera which provides a great persepcive very near the water level.
This isn’t his only floating creation. He’s got a second rig that was used to film some of the footage of this one.
Continue reading “Water Strider robot does it with Lego parts”