Rongge

Tandem Doorbell Circuit Diagram .The author had a problem: the neighbors  had exactly the same type of doorbell as he did (actually a 50 Hz buzzer), so it wasn’t always clear who needed to answer the door. To avoid confusion, the author augmented the existing doorbell with a wireless model a reasonably inexpensive option at current  prices. All that was necessary for this was to arrange for the existing button and wiring to also actuate the wireless doorbell.  Tandem Doorbell Circuit Diagram The author opened up the button enclosure of the wireless doorbell and used a multi-meter to find out which set of contacts were closed when the button was pressed. This is where the relay output should be connected (see the schematic diagram). The circuit is virtually self-explanatory: when the existing doorbell button is pressed to actuate the  buzzer, the voltage is rectified by the bridge rectifier and regulated at 5 V by the 7805. This voltage drives the relay directly, causi...

This circuit will light a lamp at a remote location when the doorbell switch is pressed. This circuit should only be used with the solenoid type doorbells, the electronic type that play tunes will not work here.  It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from the doorbell batteries or transformer. A series resistor, R1 is wired in series with the doorbell and reduces current flow, thereby increasing battery life. The value of R1 is chosen so that about 0.6 to 0.7 volts is developed across it, when the doorbell switch is pressed. I used a combination of a 22 ohm resistor in parallel with a 50 ohm. The voltage drop across R1 is sufficient to switch on the transistor, the lamp in series with the collector will then illuminate. I also used an electromechanica...

This Discrete Sliding Tone (Frequency Ramp) Doorbell circuit produces a low tone that will slide up to higher frequency. The equivalent total resistance connected between the base of Q1 and ground (Rbg) , and coupling capacitor  C1  determines the AF oscillator’s frequency. The resistance (Rbg) is equal to (R2+R1)R3.   Here is the schematic diagram of the circuit. The R2 is used to set the initial bias condition, adjusted to produce a pleasant low starting frequency doorbell tone. D1 will start to conduct when Capacitor C3 charge through R6 until it reaches D1 bias  voltage level.  Then the value of Rbg is paralleled by R4 and D1, and R5-D2-D3, and the values of diode’s equivalent resistance is gradually decreased as the C3 voltage ramp up.  This decreasing resistance value make the output tone slides up in frequency.  Two different diode path is provided to extend the linear area of diode conduction transition slope. With two path with different ...