This electronic music maker uses an astable oscillator circuit that is controlled by a photocell. The light falling ..
When the doorbell switch is pressed, the two monostable stages are activated in sequence, applying bias to a pair of voltage-controlled resistor stages. These then modulate the outputs from a pair of tone generators. The resulting signals are fed to an audio amplifier, ..
It is often desirable for a single doorbell to be operated by two buttons, for instance, one at the front door and the other at the back door. The additional button, S2 in series with the break contact of relay Rel, is connected in parallel with the original bell-push, SI. When S2 is pressed, the bell voltage is rectified by D1 and smoothed by CI. After a time, t = R{R2C2, the direct voltage across C2 has risen to a level here T1 switches on. Relay Rel is then energized.....
When SI is depressed, an initial positive voltage is placed on C2 and the noninverting terminal of Ul. The circuit o..
When the pushbuttons at either door are depressed, this circuit generates a different tone for each door. Tones are ge..
This circuit uses only one IC, produces a pleasant tone, and sports a single control for adjusting the tone"s chiming rat..
When the door is pushed, you hear a whisper that "slide up" to a higher frequency. The oscillator frequency is determined by AF coupling capacitance, C 1 and the value of the resistor connected between the base of IQ and the earth. This resistance, RBG is equal to (Ri + R2) RJ. First, suppose that 51 is closed and R2 have been adjusted to produce a pleasant, low frequency tone. The capacitor C3 charges through R6 until it reaches such a tension that will cause diode Dl to.....
8 to 15 Vac is applied to terminals C and D, which produces a dc voltage across R2, and turns on Ql. This connects the bat..
With values shown, this simple circuit will permit one operation every 10 seconds or so. Capacitor C1 charges through Rl when the button is released..
This very simple and self-powered device was conceived to allow a person to monitor if someone has rung his home door-bell when he was out. As most door-bells use 12Vac supply, the circuit must be simply connected to the two door-bell-coil leads...
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...
This schematic will activate a beeper in the basement, whenever the front doorbell is pressed...
The device described here does just that. The circuit connects to the doorbell circuit - taking power from the 18 VAC from the doorbell transformer and switching power to the doorbell circuit most of the day. The user interface is a pushbutton, a toggle switch, and two LEDs. One LED - the green one -blinks at 1 Hz, just to give me some comfort that the circuit is working. The amber LED glows whenever the doorbell is disabled. To set the timer, you just push the button.....
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 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...
In all the houses exist the bells in the door. All want, they have the possibility of being possible to change the intensity, the tone of sound. With this circuit we have this possibility. With the materials round the gates, we can change the sound. For the materials that exist in the circuit the frequencies are roughly 5 KHZ and 2 KHZ. The circuit functions only for small time interval afterwards the pressure of switch. Simultaneously with the sound we have also optical.....
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...
M1 is a clamp connected to the 24V (dc or ac) power from the gate opener. The diode bridge rectifies the alternate voltage (should the opener use dc current, it merely adjust the positive and negative rail to match circuit polarity), in order to get the power required by the 24 V relay. The same potential, limited in current by the series resistor R1, feeds the 5V regulator IC1. The 5V stabilized voltage from IC1 powers the Nutchip; the R3-C5 network ensures proper RESET.....
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...
The transmitter circuit is made up of two building blocks - the 303MHz RF oscillator and the 32kHz crystal controlled oscillator. The 303MHz oscillator consists of a self-oscillating circuit made up of the coil on the PC board and a 9p (9 puff) capacitor (actually 4p and 5p in parallel). The circuit starts-up by the transistor producing noise. This rising-and-falling signal on the collector is passed to the parallel tuned circuit (the tank circuit) and the base sees a.....
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