Doorbell Circuits

This circuit is a modified "Hartley Oscillator" with a couple extra parts. T1, the LT700 (or equivalent, is a small center tapped (ct) audio transformer with an impedance of 1000 ohms at 1000 hertz. The secondary of this transformer has an impedance of 8 ohms. Usually noted as 1K:8 ct.

This circuit is a modified hartley oscillator with a couple of extra components included. The transformer is a small audio transformer, type LT700. The primary is center tapped with an impedance of 1Kohms at 1KHz . The secondary has an impedance of 8 ohms. The inclusion of R1 and C1 give this oscillator its characteristic "chirp". As the 100u capacitor charges via the 4.7K resistor, R1 the bias for the transistor is cut off.

This simple and cost-effective door bell circuit is based on IC 8021-2 from Formox Semiconductors (Website address: fortech@mantramail. com). It is an 8-pin DIP IC whose only four pins, as shown in the circuit, have been used.

The circuit in Figure 1 prevents damage to the chime and improves the chime's effectiveness by repeating the chime strike for as long as the pushbutton remains depressed. The circuit controls both front and rear chimes.

This is a circuit that could be used as a doorbell system like those that most homes have. From what I can tell, pressing the switch triggers the IC to oscillate and send electricity through the transistors to power the speaker. The IC type is not listed, but I am guessing that it is a 555 Timer.

This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors. The count may be expanded for up to 99 visits by cascading two CMOS 4026 IC's and using an additional 7 segment display. This is achieved by wiring pin 5 ( the 10's output ) of the first CMOS4026 to pin 1 (the clock input) of the second IC.

If you can't hear your doorbell when you are in your basement try this circuit. This circuit takes advantage of the 24vac power source located near the furnace. Using a simple current transformer technique, the circuit sounds a beeper whenever the main door chime is activated.

This schematic will activate a beeper in the basement, whenever the front doorbell is pressed.

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.

The loudspeaker is a 8 Ohm type and must be larger than 200milli-Watt. I used a 2Watt type, but anything over 0.2W will do. It really sounds like a bird and when you release the doorbell button the sound slowly fades away. I have used this circuit in my house for over 20 years and even build the "Birdie" for others. Although an old circuit, the experimentation and the final results still give a punch. Remember to Have fun!