How Things Work

How Remote Controls Work

2008-01-27T14:43:00.000-08:00

If you are like most Americans, you probably pick up a TV remote control at least once a day. Look inside and see how they work:

The remote control's job is to wait for you to press a key, and then to translate that key-press into infrared light signals that are received by the TV. When you take off the back cover of the control you can see that there is really just 1 part visible: a printed circuit board that contains the electronics and the battery contacts.

You can see an integrated circuit (also known as a chip) . The chip is packaged in what is known as an 18 pin Dual Inline Package, or a DIP. To the right of the chip you can see a diode, a transistor (black, with three leads), a resonator (yellow), two resistors (green) and a capacitor (dark blue). Next to the battery contacts there is a resistor (green) and a capacitor (tan disk). In this circuit, the chip can detect when a key is pressed. It then translates the key into a sequence something like morse code, with a different sequence for each different key. The chip sends that signal out to the transistor to amplify the signal and make it stronger.

UPC Bar Label

2008-01-27T12:34:00.000-08:00

If you go look in your pantry right now, you will find that just about every package you see has a UPC bar code printed on it. In fact, nearly every item that you purchase from a grocery store, department store and mass merchandiser has a UPC bar code on it somewhere.

"UPC" stands for Universal Product Code. UPC bar codes were originally created to help grocery stores speed up the checkout process and keep better track of inventory, but the system quickly spread to all other retail products because it was so successful.

UPCs originate with a company called the Uniform Code Council (UCC). A manufacturer applies to the UCC for permission to enter the UPC system. The manufacturer pays an annual fee for the privilege. In return, the UCC issues the manufacturer a six-digit manufacturer identification number and provides guidelines on how to use it. You can see the manufacturer identification number in any standard 12-digit UPC code, the UPC symbol printed on a package has two parts:

The machine-readable bar code
The human-readable 12-digit UPC number

The manufacturer identification number is the first six digits of the UPC number -- 639382. The next five digits -- 00039 -- are the item number. A person employed by the manufacturer, called the UPC coordinator, is responsible for assigning item numbers to products, making sure the same code is not used on more than one product, retiring codes as products are removed from the product line, etc. In general, every item the manufacturer sells, as well as every size package and every repackaging of the item, needs a different item code. So a 12-ounce can of Coke needs a different item number than a 16-ounce bottle of Coke, as does a 6-pack of 12-ounce cans, a 12-pack, a 24-can case, and so on.

The last digit of the UPC code is called a check digit. This digit lets the scanner determine if it scanned the number correctly or not. Here is how the check digit is calculated for the other 11 digits, using the code 63938200039

Add together the value of all of the digits in odd positions (digits 1, 3, 5, 7, 9 and 11).6 + 9 + 8 + 0 + 0 + 9 = 32
Multiply that number by 3.32 * 3 = 96
Add together the value of all of the digits in even positions (digits 2, 4, 6, 8 and 10).3 + 3 + 2 + 0 + 3 = 11
Add this sum to the value in step 2.96 + 11 = 107
Take the number in Step 4. To create the check digit, determine the number that, when added to the number in step 4, is a multiple of 10.107 + 3 = 110
The check digit is therefore 3. Each time the scanner scans an item, it performs this calculation. If the check digit it calculates is different from the check digit it reads, the scanner knows that something went wrong and the item needs to be rescanned.

2006-09-28T15:04:00.000-07:00

STING RAY

Some AStingray-related fatalities (in humans) are extremely rare, partly because a stingray's venom, while extraordinarily painful, isn't usually deadly -- unless the initial strike is to the chest or abdominal area.

Australian bull ray, estimated to weigh about 220 pounds. Australian bull rays can be up to 4 feet wide and 8 feet long -- all stingrays use the same attack mechanism regardless of size. The mechanism is called a sting, up to 8 inches long in a bull ray, located near the base of the tail. The sting contains a sharp spine with serrated edges, or barbs, that face the body of the fish. There is a venom gland at the base of the spine and a membrane-like sheath that covers the entire sting mechanism.

When a stingray attacks, it needs to be facing its victim, because all it does is flip its long tail upward over its body so it strikes whatever is in front of it. The ray doesn't have direct control over the sting mechanism, only over the tail. In most cases, when the sting enters a person's body, the pressure causes the protective sheath to tear. When the sheath tears, the sharp, serrated edges of the spine sink in and venom flows into the wound.

A stingray's venom is not necessarily fatal, but it hurts a lot. It's composed of the enzymes 5-nucleotidase and phosphodiesterase and the neurotransmitter serotonin. Serotonin causes smooth muscle to severely contract, and it is this component that makes the venom so painful. The enzymes cause tissue and cell death. If the venom is introduced into an area like the ankle, it can usually be treated. Heat breaks down stingray venom and limits the amount of damage it can do. If not treated quickly enough, amputation might be necessary. But if the venom enters the abdomen or chest cavity, the resulting tissue death can be fatal because of the major organs located in the vicinity. If the spike enters the heart the results are fatal.

While a stingray's venom can do serious damage, the most destructive part of the sting mechanism can actually be the barbs on the spine. The sharp tip of the sting enters a person pretty smoothly, but its exit is roughly equivalent to backing up over those "severe tire damage" blades. Remember that the points of the barbs are facing the stingray. Even if venom weren't involved at all, pulling the spike out of a human's chest or abdomen could be enough to cause death from the massive tearing of tissue that results.

Defrosting a windshield

2006-09-23T12:59:00.000-07:00

What's the best way to defrost ice froma windshield:

What's better Cold Air or Warm Air?

If you can't alter the air's humidity, warm air will definitely heat up your window faster and defrost it faster than cold air. The only problem with using hot air is that rapid heating can cause stresses on the window and its frame because the temperature will rise somewhat unevenly and lead to uneven expansion. Such stress can actually break the window, "On coldest days in winter, if you turn up the heat full blast to defrost the windshield and the outside of the window still are covered with ice, after about 10 minutes of heating, the windshield will "pop" and a fracture the winshield.

About the humidity caveat: if you can blow dry air across your windshield, that will defrost it faster than just about anything else, even if that air is cold. The water molecules on your windshield are constantly shifting back and forth between the solid phase (ice) and the gaseous phase (steam or water vapor). Heating the ice will help more water molecules leave the ice for the water vapor, but dropping the density of the water vapor will reduce the number of water molecules leaving the water vapor for the ice. Either way, the ice decreases and the water vapor increases. Since you car's air condition begins drying the air much soon after you start the car than its heater begins warming the air, many modern cars concentrate first on drying the air rather than on heating it.

Diesel vs Gas Engines

2006-09-15T16:02:00.000-07:00

What is the difference between spark ignition engines and diesel engines?

Just before burning their fuels, both engines compress air inside a sealed cylinder. This compression process adds energy to the air and causes its temperature to skyrocket.

In a spark ignition engine, the air that's being compressed already contains fuel so this rising temperature is a potential problem. If the fuel and air ignite spontaneously, the engine will "knock" and won't operate at maximum efficiency. The fuel and air mixture is expected to wait until it's ignited at the proper instant by the spark plug. That's why gasoline is formulated to resist ignition below a certain temperature.
The higher the "octane" of the gasoline, the higher its certified ignition temperature. Virtually all modern cars operate properly with regular gasoline. Nonetheless, people frequently put high-octane (high-test or premium) gasoline in their cars under the mistaken impression that their cars will be better for it. If your car doesn't knock significantly with regular gasoline, use regular gasoline.

A diesel engine doesn't have spark ignition. Instead, it uses the high temperature caused by extreme compression to ignite its fuel. It compresses pure air to high temperature and pressure, and then injects fuel into this air. Timed to arrive at the proper instant, the fuel bursts into flames and burns quickly in the superheated compressed air. In contrast to gasoline, diesel fuel is formulated to ignite easily as soon as it enters hot air.

How a Relay Works

2006-09-14T14:59:00.000-07:00

Relay construction are amazingly simple devices. There are four parts in every relay:
Electromagnet, Armature that can be attracted by the electromagnet, spring and a set of electrical contacts The following figure shows these four parts in action:

The relay consists of two separate and completely independent circuits. The first is at the bottom and drives the electromagnet. In this circuit, a switch is controlling power to the electromagnet. When the switch is on, the electromagnet is on, and it attracts the armature. The armature is acting as a switch in the second circuit. When the electromagnet is energize, the armature completes the second circuit and the light is on. When the electromagnet is not energize, the spring pulls the armature away and the circuit is not complete. In that case the light is dark

When you purchase relays, you generally have control over several variables:

1) The voltage and current that is needed to activate the armature
2) The maximum voltage and current that can run through the armature and the
armature contacts
3) The number of armatures (generally one or two)
4) The number of contacts for the armature (generally one or two)
5) Whether the contact (if only one contact is provided) is normally open (NO) or normally
closed (NC)