Electricity for the 4-H Scientist Part 12

For Further Information

Check with your leader, then ask your power supplier or a local electrician to tell you about safe electrical wiring, connections and fixtures.

+-------------------------+-------------+------------------------+ |Hazard | Location |What I Did | +-------------------------+-------------+------------------------+ |_Loose p.r.o.ng on lamp plug|Living Room |Replaced with new plug_ | +-------------------------+-------------+------------------------+ |_Cracked insultor on |Back of house|Notified power _ | |_service wire in house | |supplier_ | +-------------------------+-------------+------------------------+ |_Conduit not securely |Bas.e.m.e.nt by |Notified parents_ | |_clamped to box |fuse box_ | | +-------------------------+-------------+------------------------+ |_Extension cord, old and |Bas.e.m.e.nt, by |Replaced with new_ | |_worn |washing |rubber-covered one and_ | | |_machine |protected it from _ | | | |_water_ | +-------------------------+-------------+------------------------+

LESSON NO. B-10 Credit Points 3

HOW ELECTRIC BELLS WORK--FOR YOU

When 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 Do

1. 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 Lot

Electric 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 cla.s.ses 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--Electromagnetism

If 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 b.u.t.ton, 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.

[Ill.u.s.tration: Figure 1]

You will see that the current pa.s.ses 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 b.u.t.ton.

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 b.u.t.ton is pushed, are made by connecting the armature with the screw by means of a flexible wire.

A Special Kind of Electricity

Most 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 Them

The push b.u.t.ton is the most common means of control. You can use one b.u.t.ton to control several bells, or several b.u.t.tons to control one bell, or have several b.u.t.tons control several bells. Because low voltage is used, adding extra b.u.t.tons 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 cla.s.s 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.

[Ill.u.s.tration: Figure 2]

Pick the Right Bell or Buzzer

Some 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.

SOME TYPICAL JOBS FOR BELLS & BUZZERS

-------------------------------------------------------------------- Number and Type of location Number and bell or of bells Type of location Job buzzer and buzzers control of controls --------------------------------------------------------------------- Summon others In the house-- Enough to Push- One at the to the small to cover all b.u.t.tons telephone telephone medium buzzers usual work and each In locations extension outbuildings-- phone medium to large bells Outdoors-- large weatherproof bell All transformer- powered --------------------------------------------------------------------- Notify club Medium to large One may be Hose One--in member that bell-- enough--if diaphragm the car is at his transformer- mounted on driveway produce stand powered the back of ----------------------- the stand (Complete driveway including control, are available, ready to plug in.) -------------------------------------------------------------------- Warn of power Battery-powered One near Relay, One, at failure to buzzer, medium the held open main incubator or size poultryman's as long as switch of brooder bedroom power is on, hatchery closed by or spring if brooder interruption house occurs -------------------------------------------------------------------- Warn of Battery-powered One, in or Temperature One, with dangerously buzzer, medium near the detector bulb warm size kitchen (sensitive inside temperature thermostat) freezer in freezer ---------------------------------------------------------------------

How to Plan Your System

To 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 b.u.t.ton 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 b.u.t.tons and bells that you have planned.

Inside, you will connect your transformer and the various b.u.t.tons 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).