How Remote Controls Work

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

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.