  Credit Points 3 HOW ELECTRIC BELLS WORK—FOR YOUWhen was the last time you wanted to get a simple message like "You're wanted on the telephone," "There's someone here to see you, "or "There's a car in the driveway," to someone around your place? Did you have to walk or run some distance and perhaps shout, too, to be heard by the other person? Perhaps you had to stop some other work, or interrupt your favorite kind of fun, to do this bit of messenger work. If the nature of the message is like one of those mentioned, and the number of people in hearing is not too great, then perhaps you can use bells or buzzers or both to do some of your messenger work for you. Even though a bell or a buzzer can't talk, it can convey a message. What to Do1. Learn how bells and buzzers work, and learn about the many different kinds. 2. Plan and install a bell system for your home or farm. Bells and Buzzers Can Tell a LotElectric bells and buzzers use the same basic principle as the telegraph system, invented by Samuel Morse in 1840. Although not as important today as it was before radio, telephone, and teletype became common, the telegraph is still in use. Bells and buzzers, however, are very common and have many uses. They are most often seen in the form of doorbells, and rare is the new home that does not have one or more. Service stations have bell systems to let the operator know that a car is waiting at the gas pumps. A clock signal reminds the homemaker when the cooking time is completed. Children are called to and released from school classes by means of bells and buzzers. Also, various alarms employing bells and buzzers warn us when it's time to get up, or even that the place is on fire, or that a burglar is trying to break in! Let's find out how bells and buzzers work, what different kinds there are, the different ways you can control them, and how you can put them to work for you. You'll find that buzzers and bells can help you with your 4-H projects, and with the proper controls, can be your eyes and voice in a dozen places at once. Why They Buzz or Ring—ElectromagnetismIf we were to look at an electric bell with the cover off, we'd find that it would be very much like Figure 1. A push on the button, which is just a switch that is normally held "open" or off by means of a spring, sends the current from the battery or transformer through the circuit. Figure 1 You will see that the current passes first through two small coils of wire, and each coil has at its center a piece of soft iron called the core. When the current is on, the core becomes magnetized and attracts another piece of iron called the armature with its clapper attached. This action rings the bell, but it also breaks the current by pulling the spring away from the screw on its return to the power supply. With the power off, the electromagnet lets the spring return the armature to its normal position, contact is made again, and the cycle starts all over again—just as long as you continue to push on the button. Buzzers work exactly the same way, except that they do not have a bell and depend instead on the vibration of the armature for a noise that's not as loud or as musical. Gongs or chimes, that strike only once when the button is pushed, are made by connecting the armature with the screw by means of a flexible wire. A Special Kind of ElectricityMost buzzers and bells work on a much lower voltage than you normally find in the wires in your house. Some are made to work at 6 volts, others at 10 volts, and still others at slightly higher voltages. You can get these low voltages by using one or more batteries, or by using a transformer connected to your house current. Most bells and buzzers are now powered through transformers. How to Control ThemThe push button is the most common means of control. You can use one button to control several bells, or several buttons to control one bell, or have several buttons control several bells. Because low voltage is used, adding extra buttons is simple, inexpensive, and safe. Buzzers and bells can also be controlled by: clocks, as in the interval timer on an electric range or in a school class bell system; temperature detectors, as in a fire alarm or freezer alarm; door and window trips, as in a one-man repair shop or in a burglar alarm; and treadles, as in the driveway of a service station. Figure 2 Pick the Right Bell or BuzzerSome of the many different types of bells, and various ways of controlling them are suggested in the table below. Just remember that no matter what the job or conditions, you can probably find a bell or buzzer and controls that suit your need.
How to Plan Your SystemTo save your time and steps when the telephone rings for someone else in your family who is some distance away, you can install a simple bell or buzzer system to summon that person. First, you must plan what you are going to do. On a large sheet of paper, draw to scale (roughly) a plan of your house and grounds, including those places where phones are located. It will help if you rule off your paper in 1/8" or 1/4" squares and let each square equal one foot. Show the location of poles supporting your wiring. Next, pick out those areas where you or others would likely be when someone else would answer the phone and want to call you to it. After you have thought about this, and talked it over with members of your family, show locations on your plan where you think you would like to have buzzers or bells, and show a button beside each telephone. (Generally, you should have a bell or buzzer near each phone, also.) Figure 3 shows diagrams of various types of systems, and will help you determine the number of wires you will have to install to connect the buttons and bells that you have planned. Inside, you will connect your transformer and the various buttons and bells with ordinary indoor bell wire. Outdoors, however, you should use weatherproof 2-wire or 3-wire telephone twist. Show on your plan the distances that must be traversed by each type of wire, and show the number of conductors in each. Don't overlook the vertical distances (one floor to another). Figure 3 Materials You'll NeedBecause no two situations are just alike, it will be necessary for you to make your own list of materials. As a guide, however, here is a list of typical materials, with the quantities left blank, for you to fill in as your own requirements and measurements dictate.
Because your transformer must be wired into your regular house current, you should have some help on this from an electrician or other qualified person. Also, you should get that person to review your plans and materials list before you place an order. Install According to Your PlanWith the aid of an electrician or other qualified person, install your transformer, and test it. You may then go ahead and complete your signal system, checking carefully with your plan, and making sure that your installations are both electrically and mechanically secure. Test your system in all possible ways that it might be used. Demonstrations You Can GiveBuild a demonstration board incorporating a farm or home layout, with pushbuttons or other controls and bells and buzzers appropriately located. Show and tell how the system would save time and energy. Show and tell how some of these work, and their value: power-off alarm, freezer alarm, fire alarm, driveway alarm. For More InformationAsk your power supplier or your nearest electrical supply house for catalogs or literature on various types of signal systems, or ask a dealer to show you equipment he has in stock. | ||||||||||||||||||||||||||||||
|
