ringer
Make your doorbell ring like a telephone
tinmoorthy
Keywords :
two tone ringer IC, ceramic transducer, LS 1240, Home Electronics, HobbyWhy should your door bell ring like a telephone? Because it is natural. What does that mean? Let me explain.
Vasnt Sathe was the Minister for Information & Broadcasting then. He had determined to bring color to the TV. Before that the TV had no color. It was black & black. Sometimes white & white. Sathe had reason for the induction of color into the idiot box. He said the nature is in color; therefore the TV shall have color. Amen
I have often heard the telephone ringing in the TV and had mistaken it for the real stuff. Have your ever wondered why? The telephone ringing is synthetic and no matter how you produce it has the same flavor -- like the lacking variety of the rubber stamp outputs
Other bell chimes have a few parameters that can vary from case to case. In being plain bland, nothing comes close to the telephone ring, Om Jaya Jagdish Hare and Jingle Bells. All of them are synthetic produced by the same die at the factory that has manufactured several millions of the chips already
In any case I thought that normal door bells take lot of current, that too inductive (whatever that means) and cause disturbance to the other devices like the TV. I wanted a simple hook up that will be energy efficient. And the telephone ringer fitted that bill smugly
I had engaged a consultant for this purpose. He brought a ringer IC and a ceramic transducer. These hi funda apellations do not scare me easily. He explained that a two-tone ringer is a compact component replacing many analogue devices. I reluctantly agreed to go with it. So far as the ceramic transducer is concerned, no discussion was necessary, he said -- because it is most energy efficient. It produces the maximum noise for given input -- much like my next door dog!
Two things are specific to this paper. The first one is the ringer IC to code LS 1240. It is an eight pin IC, preferably to be mounted on an IC socket. The second is a ringer transducer, somewhat round in shape, thin, often black and two wires coming out for external connections. It tests open for the ohm-meter and is (fatally) allergic to domestic current. Many shops sell these -- but some scouting and coaxing the shop keepers are certainly indicated
For myself my consultant brought them from a good working telephone. I felt silly. You do not cannibalize a good device just because you needed a few components. You do not buy an ice cream shop merely for two cones of softy
"No" my Consultant advised, "Tomorrow you will need the chairs, the counter and possibly the goodwill of the ice cream shop. So I have got them in advance." The rest of the telephone components will not be wasted, according to him. He would discover new applications -- so I was not to worry
Only a few words about the assembly. The first one is about the resistor and the capacitor. You adjust them for the tones and modulation. The second is about the power supply -- that needs to be adjusted so that the supply to the device does not to exceed say about 18 volts (DC of course, across pins 2 and 7 latter being positive). This is manipulated by a series resistor. Since the conversion is so good, the current drain is seldom noticeable. For this one feature alone I am now ready to break another telephone
Aside : For those who are new to the concept of the ICs few preliminary words are appropriate. The pins from an IC are many. Fortunately the ringer IC is only an eight pin and considered to be at the beginners' level. The IC pin counting is to be exercised looking at the IC from the component side. That is as opposed to the (printed) wiring side. In simple terms if you are holding the IC and are able to read its code, you are looking at it from the component side. Otherwise it is upside down.
When you are so viewing the IC you need to locate the inverted C-shaped notch which is a marker. Keep the notch to your left. The nearest pin (on a Dual In line Plastic Package) below that is pin #1 (Many times there is otherwise a circular marker nearest to Pin 1). Counting proceeds counter-clockwise. 1,2,3 & 4 on the bottom line, left to right. And 5,6,7 & 8 on the top line right to left. Thus pins 1 and 8 face each other on a vertical plane. Similarly the pairs of pins 2 & 7, 3 & 6, and 4 & 5
Wiring on the IC for non-professionals is cumbersome. No IC will tolerate amateurish soldering -- they are sensitive to uncontrolled heating. IC socket is a good substitute. Soldering on the socket has the same kind of hassles though. Besides for general purpose applications (that is without a Printed Circuit Board) discrete wiring is the only option open. Given the vulnerabilities of the soldering, the best route is to take the so called wire wrapping. The wrapping practice needs some considerable investments in the form of tools (however simple they may be) and skill. Beginners will do well to consult professionals for the wiring the ICs
