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AC – alternating current. An electrical current that reverses directions at regular intervals. Wall power, or mains, is AC and in North America, it cycles 60 times per second, while in England and Australia, it cycles 50 times per second.

Amps (amperes). A unit of electrical current, an amp is the amount of electricity being drawn through the power system. A product that draws 10 amps uses twice as much electricity as a product that draws five amps. See also Electricity basics.

Audacity. An open source (both free to use and source code freely distributed) digital audio manipulation application. It is available for Windows, Mac OS X, Linux and BSD (though Windows 7 support is only "provisional"). It can record audio, provide editing functions for shortening the length of audio files or handle mixing, spectrum analysis or change in pitch and/or speed. It imports and exports WAV, AIFF, MP3, FLAC and — with plugins — WMA, AAC, AMR and AC3. It is available at and instructions are at

BNC – Bayonet Nut Connection. A type of common radio frequency connector used on coaxial cables. See RG-58.

BOM – Bill Of Materials. A list of equipment used in building the device depicted in a drawing. Usually contains an Item number, Number of parts used, Description, Manufacturer, Manufacturer part number, etc.

C7, C9 light bulbs. Known as the “traditional” Christmas light, these types of strings had their hey-day in the 1950s and 1960s. Many lighting hobbyists switched to “mini” bulbs in the 1970s. The "c" stands for candle, while the number indicates the diameter of the bulb (7 indicating 7/8-inch diameter and 9 indicating 9/8-inch — or 1-1/8-inch diameter). The C7 bulb is about 2-inches tall, while the C9 is about 3-inches tall. The C7 uses the candelabra base (screw-in), while the C9 uses the intermediate base. Both sizes come in both clear and opaque colors and both come in 7-watt versions, while the C7 comes in a 2.5-watt version and the C9 in a 3.5-watt version. The maximum number of 2.5-watt lamps per 15-amp circuit is about 575 (or 765 lamps per 20-amp circuit) or 300 lamps per outlet, while the maximum number of 7-watt lamps per 15-amp circuit is about 200 (274 per 20-amp circuit) or about 125 lamps per outlet.

Capacitor. An electrical component that stores an electric charge and releases it when its needed. Typically used in Christmas lighting as a filter in power supply circuits.

Circuit. The path (usually wire) through which current flows between an electrical energy source and an electrical device, appliance or fixture.

dB – decibel. A unit of relative sound or radio transmission intensity.

DC – direct current. An electrical current that flows continuously in one direction. Batteries and fuel cells produce direct current and alternating current can be rectified and changed into direct current with diodes.

Decoupling capacitor. A capacitor that is included in circuits with microcontrollers to insure that voltages don’t dip and spike elsewhere around the circuit because of the needs of the microcontroller. Like a water tower in a community, the circuit slowly fills up the decoupling cap with electricity. When the microcontroller needs a burst of energy (or, in the analogy, if somebody needs to flush three toilets at once), the decoupling cap provides the needed energy without the water pressure throughout the community dropping.

Diode. An electrical device that will allow current to pass in only one direction.

DIP – Dual In-line Package. A method of mounting integrated circuits, microcontrollers and other electronics components on printed circuit boards. Sometimes called “through-hole package,” because holes are drilled in the PC boards and the package is soldered to the board on the side opposite the package. Compare this with “surface mount,” where components are mounted to the PC board on its top side by soldering leads directly to pads.

Dipole. A basic radio antenna that consists of two elements, each of equal length. The length of the elements is an algorithmic function of the frequency over which the broadcast is being made. It’s used in Christmas lights by FM transmitters that are used to broadcast music with the light shows.

Electricity basics. The flow of electrons typically over wire, electricity is energy converted from fuels or natural resources and distributed to homes and businesses via a grid of utility companies. Electricity has three basic units: voltage, current (measured in amps) and resistance (measured in ohms). The basic equation of electrical engineering is that amps = volts divided by ohms. The fourth basic element of electricity is watts, which is volts times amps. The most common analogy used to describe electricity is that of plumbing and water: the pressure of water in a pipe is like voltage, while the flow of the water in a pipe is like amps.

Electrolytic. A type of fixed capacitor. See capacitor.

Farad. A unit of measurement for electrical capacitance. See capacitor.

FCC – The Federal Communications Commission. The FCC was established by the Communications Act of 1934 and is charged with regulating interstate and international communications by radio, television, wire (telegraph, telephone), satellite and cable.

FCC Part 15. A section of the Federal Communications Commission’s rules and regulations that deals mainly with unlicensed transmissions. In the Christmas light world, FCC Part 15 is discussed because it regulates the way low-power FM transmitters, which are used in the Christmas lights community to broadcast the music that accompanies the light shows, should work. The general consensus in our community is that one way of measuring whether an FM transmitter might meet Part 15 rules is that it should not transmit further than 250 feet away from its antenna.

Fuse. A device designed to make electronic and electrical circuits safer by breaking ("blowing") in the event of an electrical short circuit or overload. A fuse will blow before wires become so hot they catch on fire.

GFCI – Ground Fault Circuit Interrupter. An electrical safety device installed in a power panel, sub-panel or outlet box that instantly shuts off the electricity when a leakage to ground occurs. This leakage can increase the risk of electrical shock. A GFCI should be used in all outdoor high-voltage environments and the device should be tested on a regular basis.

Grounded/grounding. A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth, or to some conducting body of relatively large extent that serves in place of the earth.

Heat sink. A piece of metal attached to an electronics component – microprocessor, microcontroller, Triac, optoisolator – that serves to dissipate or absorb unwanted heat. Many electronics components have two ratings, a lower one when a heat sink is not used and a higher one where a heat sink is in place. Also called a dissipator.

LED – Light Emitting Diode. A solid-state, semiconductor device that converts electrical energy directly into light. LEDs show up in Christmas lighting in two contexts: the first is as a power or signal indicator in controllers or SSRs, while the second is their use as a substitute for incandescent lamps. LED Christmas light strings use about one-tenth the energy of an incandescent lamp and have a crystal-clear color brightness that incandescents cannot achieve.

Mains. The alternating current electricity provided by the utility company; a Britishism/Aussy slang for the American phrase “wall power.” In North America, typically 120 volts, AC. In the United Kingdom and Australia, typically 240 volts, AC.

Microcontroller. A computer-on-a-chip that emphasizes high integration, low power consumption, self-sufficiency and relatively low cost. Typically, a microcontroller has flash-type read-write memory allowing a programming station (usually called a PIC programmer) to enter in task-specific programs, which can be written in programming languages such as C, C++, BASIC or even in assembly code (which, of course, is the most efficient).

Mini-lights. Incandescent bulbs that are about 7/32nds of an inch in diameter, they come in strings as short as 35 bulbs and as long as 400 bulbs. Officially known as the T1-3/4. The strings are wired in series and parallel, usually in 50-bulb groups (the 50 bulbs are in series which are then wired parallel to the others, making 100-, 150-, 200-, 250-, 300-, 350- or 400-bulb strings). Pretty universally, strings that are grouped by 50 bulbs can be cut down to 50-bulb strings. Mini-lights that are grouped by 50s use 2.5-volt, 170 mA bulbs, while 35-bulb strings use 3.5-volt bulbs. Mini-light bulbs are traditionally painted with a transparent paint, which can under severe or extended weather begin to chip or fade.

MOC3023. A six-pin DIP 400V random phase Triac driver output optocoupler from Fairchild Semiconductor. It provides both Triac services and optoisolator services in one package.

NIC. Network interface controller or network interface card. The hardware that allows a personal computer to access a network, most commonly an Ethernet network. In early PCs there was no network interface controller, so it was offered as an expansion card. Virtually all modern personal computers have a network interface controller built into the motherboard.

Ohms. The measure of resistance to the flow of an electric current (the resistance through which one volt will force one amp). Resistors in electronic circuits are measured in ohms, as is the voltage drop of an electrical wire. See also Electricity basics.

Optoisolator (opto, optocoupler). A device that insures that a non-electrical barrier exists between a high-voltage environment and a low-voltage environment. It usually has some type of emitter – like an LED or a neon bulb – and an optical receiving element with a little dark tunnel between them. The high voltage causes the LED to brighten and that light then drives the low-voltage optical receiver. This way wall plug voltage doesn’t stream down low-voltage wires and into your controller or PC.

Oscillator. A circuit that produces a sustained AC waveform with no external input signal. Oscillators can be designed to produce sine waves, square waves, or other wave shapes. They are typically used in Christmas lighting to produce fading and dimming.

PCB – Printed Circuit Board. An electronics board that contains layers of circuitry that connect the various components of a system. A PCB can be mass manufactured or can be “home etched,” where a hobbyist transfers the design of the PCB to a copper-clad board, uses caustic chemicals to etch away the areas not needed and then drills the holes him or herself.

PIC. A brand name for microcontrollers from Microchip Technology Inc., it has become a generic term for any microcontroller, which is a computer-on-a-chip.

Pixel. A term traditionally used in computer graphics to identify a picture element, it has been adapted by the Christmas-lights community to refer to a tri-color (red-green-blue) LED that has an internal controller and is manufactured as a string, a strip (either rigid or flexible) or as modules. Pixels require three channels of sequencing software each, so 10 pixels are 30 channels and 50 pixels are 150 channels. Pixels can be based on any of a variety of controllers, including the TM18xx series, the LPD-6803, the WS2801, the 3001 and the GE ColorEffects chips. Further, pixels can be driven at either 5-volts or 12-volts and can have a variety of color orders. For strings, strips or modules of pixels to interoperate, they must have the same controller chip, the same voltage and the same color order (which usually means they must have the exact same manufacturer).

Polarity. The electrical condition of being either positive or negative. The direction of current between two leads or the direction of a magnetic field.

Programmer. A device that connects to a personal computer to a microcontroller to download an application from the PC to the chip. See PIC.

Resistor. A component in an electrical circuit that controls current by providing resistance. See ohm.

RG-6, RG-8, RG-11, RG-58, RG-59. These are all coaxial cables of varying thicknesses and impedance. The RG stands for “radio guide,” an old, obsolete military specification; the numbers are arbitrary. Most coax manufactured today is “RG-xx type,” because manufacturers don’t necessarily always meet the precise specifications. In the Christmas light world, you will encounter RG-58, a 50-ohm cable, because it is used in radio transmission and is discussed along with low-power FM transmitters that broadcast the music that accompanies the light shows.

RGB RGB is a type of LED that can be color controlled. The color is determined by the mixing of Red, Green, and Blue LEDs inside each physical RGB LED. RGB LEDs are packaged in both "smart" RGB (or Pixels) where each LED can be controlled individually, and "dumb" RGB where the entire set of LEDs are controlled together.

RoHS – Restriction of Hazardous Substances. A directive by the European Union that is designed to keep harmful chemicals and materials to a minimum. It is used by electronics manufacturers to denote components that meet the EU requirements.

RS232. A telecommunications protocol, Recommended Standard 232 was originally designed to connect teletypes with modems; it has survived to this day as the way computer serial ports send out data. RS232 is implemented in a variety of connectors, but is most commonly seen in the DB9 and DB25 devices. It uses nine wires and supports transmitted data, received data, request to send, carrier detect and ring indicator. It is used in Christmas lights as the physical layer between PC serial ports and Christmas lights controllers.

RS485. A telecommunications protocol, Recommended Standard 485 is typically used in building automation, the programming of logic controllers, sound system control, lighting control and video surveillance camera control. It is a two-wire system that uses a differential form of signaling that supports the transmission of data packets. It can be used over a long distance and supports multi-point connections. It is used in Christmas lights as a distribution system for light controllers signaling devices, sometimes using the DMX512 protocol.

Short – Short Circuit. An electrical connection between two points where one should not exist. A good example is too much solder on two adjacent points that cause a solder bridge.

SNR – Signal to Noise Ratio. A measure of signal strength relative to background noise. In Christmas lights, would be used in conjunction with an FM transmitter, that itself would be used to broadcast music with the light shows.

Surface mount technology; surface mount device (SMT, SMD). A method of mounting integrated circuits, microcontrollers and other electronics on printed circuit boards. The method mounts the devices on the top of a PC board rather than using holes through the board. Compare this with DIP.

SWR – Standing Wave Ratio. Usually used in the phrase “SWR meter,” which is a device coupled between a radio transmitter and an antenna and is used to tune the antenna accurately to the frequency over which the radio waves are being transmitted.

Transformer. An electro-magnetic device designed to raise or lower electrical voltage.

Transistor. A basic solid-state semiconductor that has three terminals and can be used for amplification, switching and/or detection.

ULN2803. An array of eight Darlington transistors (which themselves are arrays of two transistors) that amplify current. Often used in Christmas lights as devices to increase the current coming from a microcontroller to an SSR so that there is enough power to turn on (or off) the SSR.

Voltage drop. The loss of electrical voltage in a circuit which is determined by two main factors: the size of the wire (or wire gauge) and the length of the wire run. While it can be experienced in any circuit, it typically is more of a problem in lower voltage circuits (5 volts-24 volts). Voltage drop on a long run of wire can be helped by increasing the wire gauge, using a smaller AWG number wire.

Voltage regulator. An electronic device designed to take a higher voltage and make it conform to a specific lower voltage. Provide a 5-volt regulator with 12 volts as an input and it will put out a steady 5 volts; provide a 12-volt regulator with 13 volts and it will output a steady 12 volts. While some regulators are designed for specific voltages, others can provide a range of voltages depending upon resistance applied; variable voltage regulators can be controlled by potentiometers (i.e.: volume control), so that you can turn a knob and get various voltages depending on where the knob is.

Volts. A measure of “electrical pressure” between two points in a circuit. The higher the voltage, the more current will be pushed through the circuit. See also Electricity basics.

Wall power. The alternating current electricity provided by the utility company. In North America, typically 120 volts, AC. In the United Kingdom and Australia, typically 240 volts, AC.

Watts. A measure of the amount of electrical power drawn by a load, such as a light bulb. A watt is determined by multiplying volts by amps. A kilowatt is 1000 watts and electrical utilities measure electricity consumption by kilowatt hours. For example, if you have two 500-watt heaters, and you leave them both on for one hour, you have used one kilowatt hour of electricity. See also Electricity basics.

Wire gauge. A way of measuring the diameter of a wire. It is determined by the number of times a piece of metal is passed through successively smaller dies. So, the smaller the number (2, 4, 6, 8) the larger the diameter of the wire, while the larger the number (18, 22, 24), the smaller the diameter of the wire. Frequently expressed as AWG, meaning American Wire Gauge.

ZC Zero Cross is the point where the AC goes to zero volts. It does this just as it switches its polarity. The reason the dimmer pics need to know this is because this is the only time the Triacs can turn off. And so this is the point where the pic starts its delay to wait some part of he cycle before turning the Triac back on. If it waits half a cycle then we get 50% brightness if it does not turn it on at all it is 0% and off. So it is the heartbeat of the dimmer. It is that important. And the reason it was not on with the H11aa chip lose is because it is the part that generates the heartbeat. On the Lynx dimmers the 15k resistors and the 2k resistor make up the ZC circuit that creates the timing pulse we call the ZC.