Intercom sets are immensely of good use and almost indispensable at places where a communication website link between several persons is necessary. ITie installation on most associated with the commercially available intercoms involves the procedure that is cumbersome of this signal transmission wires, which results in increased spending and frequent problems (due to snapping of wires etc).
This article defines practical and constructional details of a simple, fail-safe, mains operated, incorporated intercom that is two-way. The circuit, as well as being multipurpose and low in expense, possesses a wide range of desirable features like in-built center that is calling self-contained solid-state power supply, activation indicator, APO (auto-power off) etc. As the circuit uses no transformers, transistors etc, it is practically zero) for giving and signals that are getting.
The circuit associated with the intercom that is two-way shown in Fig 1. I x)w-cost IC that is op-amp types the heart for the circuit. Resistor R1 drops the mains voltage to an amount that would work. This voltage is rectified, stabilised and filtered by Dl, Cl and D2 correspondingly. The 12-volt supply that is regulated acquired drives the remainder circuit. Resistors R3 and R4 tap this voltage which often biases 7 the input that is non-inverting of. Resistor R2 biases the condenser microphone. Capacitor C2 couples the same to your inverting input of IC1. Resistor R5 is employed to attenuate this input signal. Resistor R6 determines the gain of 1C1. Capacitor C4 is employed to couple the production signal to the speaker and to another set/sets, while VR1 is employed to attenuate the output signal to an amount that is suitable.
The event that is calling obtained by pressing switch S2. When S2 is pressed, capacitor C3 is introduced as a feedback element between the production and input that is non-inverting of. Id thus ! starts to oscillate and an tone that is audio generated at Uie output When switch S1 is pushed, the circuit gets deactivated and vice versa.
The PCB pattern associated with circuit and also the components positioning in the PCB are shown in Figs 2 and 3. Soldering should be done utilizing quality that is great axe and flux. Extreme care should be used in soldering the elements, especially IC1. A socket is preferred for use with IC1. The pin configuration associated with IC is shown in Fig.5.
After the soldering regarding the PCB has been done, excessive flux should be eliminated using the assistance of petrol. All connections with the PCB must be made using ribbon that is flat. The circuit are housed in a plastic cabinet that would work. The circuit, being quite compact, can be enclosed in the handset case itself.
Switch SI ought to be installed on the case in such a real way that the circuit is switched on whenever the device is lifted, and switched off when it’s held straight back in its initial place. The speaker and mic. may be fixed inside the cabinet using a adhesive that is strong. The LED should be installed on a holder that is LED. Finally, points A B and C regarding the PCB should be attached to a 3-pin mains plug using a colour that is 3-core cable.
Installation and adjustment
The adjustment regarding the circuit is quite easy. Only VR1 has become modified for the particular level that is maximum of. Keep VRl in minimum resistance position which will produce a whistling noise through the presenter. Increase the resistance that is in-circuit of so the whistling sound prevents.
I’he circuit, if used between places having common real time and mains which can be netural, needs no extra connections except individuals with the mains lines. The connections between the two sets should be produced as shown in Fig. 4. the completed intercom must always downwards be held dealing with making sure that switch SI continues to be pressed plus the circuit remains deactivated.
The circuit may be irreparably damaged if any for the three mains wires (in other words.
live, neutral or ground) arc interchanged. You need to colour code the input-output that is 3-core, utilizing red for live, black colored for basic and green for ground in all of the sets.
No an element of the circuit must certanly be moved whenever the intercom is being used since it is directly attached to the mains.
1.The circuit may be utilized as a multichannel intercom by using digital or electromechanical techniques which are switching.
2. a battery pack back-up could be given by connecting a battery pack that is 9/12-volt shown in Fig. 6.
3. Utilize the littlest feasible presenter for a construction that is compact.
4. The circuit can be used as a door-answering system after increasing the value of R6 and replacing the presenter that is small a more substantial one.
5. The call-tone regularity might be changed by changing C3.
The circuit that is completeone side) would cost around Rs 30 just, excluding the cabinet.
In Make Yourself This Special 2-way Intercom project in Jan. 92 issue, since the output of one intercom is connected towards the presenter of the set that is same just how can we expect the production to achieve the other end?
And, in place of IC 748C, can we utilize general-purpose op-amp IC 741 or any other IC that is easily available?
J. RAVINDRA Davangere
Within our home we are having typical real time and mains which are neutral but we don’t have any ground wire in our electricity board. Just how do that circuit is employed by us?
MAHAVIR D. CHHAJED
1. May I make use of IC 741 for IC1?
2. Can a security circuit be used, just in case mains wires have interchanged?
3. If the circuit is employed by me for a door-answering system. Is circuit that is one-side or both edges would be expected?
4. May I use loudspeaker as a mic.?
A. NAGABABU Rajahmundry
The elements design shows it as a carbon mic. While the right components list shows a condensor mic.! Which one is usually to be utilized?
If IC 748C just isn’t available, manages to do it be replaced by )jA741?
The circuit as such seems exceptional. This circuit was a much one which is anticipated.
SUNISH ISSAC Calicut
Mcdougal, Mr Amrit Bir Tiwana, replies:
Its quite heartening to see big money of letters from EFY readers for my intercom design. Some queries being typical replied below:
The production shall achieve one other end because the two speakers are connected in parallel.
As for IC 748 utilized, on practical verification it absolutely was found that IC 741, specifically makes |aA741 and LM741 in 8-pin DIPs, can instead be directly utilized. Outcomes are not found to be as good with a few other makes along with the TO-3 package that is metal-can RAM741 and CA741.
Although this design will continue to work most readily useful without additional wires, in lack of ground wiring you can run an extra wire, or run the circuit on batteries (9 to 12V) like a intercom that is normal.
No security circuit are feasible at a price that is reasonable is maybe not neededprovided you take care in wiring and make use of a plastic enclosure for housing the intercom.
The terms condenser mic. and carbon mic. are invariably interchangeable. It’s the component that is button-sized in cassette recorders. The concept of using a speaker is perhaps not feasible. In almost any complete case, it would be costlier than making use of a Rs 7 mic.!
For using as a doorphone, you may use one side as long as you intend to talk one-way. Otherwise, both relative edges are expected.