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Low-Cost Intercom(SL100)

2017-08-07 09:25  
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This article briefly describes the Low-Cost Intercom (SL100). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: SL100 , BC548.

The intercom circuit described here uses two transistors, an audio transformer, and a few passive components in addition to condenser microphone and low-wattage speaker (refer Fig. 1). The complete unit can be made on a general-purpose veroboard. The microphone signals are amplified by a two-stage transistor amplifier, while the speaker is driven through an audio output transformer (similar to the one used in transistor radios).

Figure:1 Circuit diagram

Figure 1 Circuit diagram

When ring button (push-to-on switch S1) is pressed, capacitor C3 gets connected between the base of transistor T2 and the top end of primary winding of audio output transformer. As a result, the amplifier circuit wired around transistor T2 gets converted into a Hartley oscillator and produces an audible tone for call-bell. To build a two-way intercom set, make two identical units with the speaker of each circuit installed near the other unit as shown in Fig. 2.



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