Each time you press the doorbell generator creates a Ding-Dong weak audio signal with the sound of bells. The signal is high in volume by the amplifier and is reproduced by the speaker. The power supply circuit provides the voltage necessary to operate. The interface circuit to connect the rings fed centrally as buildings or intercom.

The circuit is powered through the point marked V + and ground. The heart of it is the integrated HT2811, developed by the firm koreana Holtek. For the pin 1 enters the trigger pulse, telling the chip to produce the sound “Ding-Dong”. Pins 2 and 3 are connected to sets RC establishing each of the sounds (2 = “Ding” / 3 = “Dong”). Altering these components is achieved by varying the sound of bells. Pin 4 is the mass. By the pin 5 leaves the audio signal which is amplified by a pair of transistors used in darlington configuration. The terminals 6 and 7 are connected to a 680K resistor which adjusts the gain of the internal preamplifier chip. Finally the terminal 8 enters the feed to the chip which is current limited by the resistance of 100 ohms and 3.3v stabilized by means of zener diode. The 100μF capacitor filters the possible ripple left in the power line.

In case of using this bell at departments or locations where you can not modify the wiring in the bell push is necessary to use this interface. It receives at its input an AC or DC voltage and rectifies through PR the bridge rectifier whose output is filtered by continuous capacitor 470μF and subsequently attacks the small coil of a reed relay. The key to this relay trips the main circuit as would a conventional switch. The rectifier bridge (PR) can be either formed by diodes 1A 250V or more. While the voltage of the relay coil must be the same as the voltage of the previous original buzzer ring (usually 12V). While the relay can be operated without rectifying the line or filter is not suitable because the alternating current would act to relay as a buzzer, opening and closing your key 50 times per second and this can cause some damage in the mechanism after a time.

This section of the circuit adapts the voltage from the power supply required by the household the equipment. It also enables battery power for all occasions when the power fails. The transformer reduces the voltage AC 4.5v. The bridge rectifier (PR) converts AC power continuously, which is filtered by the capacitor of 2200μF. The 1N4007 diodes act as source selector system by operating the mains or batteries as needed. The fuse protects the transformer section 220v. The bridge rectifier (PR) can be any voltage which is greater than 250V and whose current is not lower than 1A. Point + V represents the output of the source, while the batteries (4 in series) input by the points + Bat and-Bat.

This metal detector electronics circuit also detects metal objects and magnets. When the magnet is near the 10 mH coil, a metal detector project can be supported by a power supply that can provide a DC output voltage of 6 volts to 12 V. If the metal is closer to the coil L1, it will produce a change in the oscillation frequency of the output, which will produce sound at 8 ohm speaker.

Parts list :
R : 47K
C : 2.2uF (2) 10uF
L : 10uH
IC : 555
Speaker 8 ohm
Supply voltage 6-12V

By adjusting the potentiometer P2 to a high pitch, can enter the circuit into oscillation by emitting a continuous whistle.In this case, we must reduce degradation of sound with the potentiometer P1. For installation components, follow closely the diagram layout.

Bell Electronic Parts list :

All resistors are 1/4 watt unless otherwise stated.
R = 68 ohms
R2 = 1 kohm
R3 = 10 Kohm
R4 = 470 ohms
R5 = 82 Kohm
R6 = 22 Kohm
R7 = 270 ohms
R8 = 10 Kohm
R9 = 47 ohms
Pl = 4.7 MohmsA.
P2 = 220 Kohm A.
Cl = 22uF16V elec.
C2 = 1uF16V elec.
C3 = 0.1 uF 100 Vpol.
C4 = 0.047 uF 100 Vpol.
C5 = 0.047 uF 100 Vpol.
C6 = .47 uF 100 Vpol.
IC1,IC2,IC3 = 741
P = Push.
3 IC Supports 8-pin

These integrated circuits operating at 5 V and 9 V battery 6F22 certainly convenient, voltage is reduced and stabilized by a 78L05 regulator. By rotating the trimmer R2 from one end to another, will change the flashing between 0.5to 3 flashes per second.

This electronic flasher circuit can be placed in bags or placed in a belt to put on waist (when cycling,walking, etc..). You will see this safety circuit is highly efficient flashing in the darkness. Moreover, nothing prevents to build a (relatively inexpensive) and set them on someplaces (legs, back, bike, scooter …) to improve visibility.

List of electronic components Led electronic flasher:
R1 …………… 2.2 kOhms
R2 …………… 10 k trimmer
R3 …………… 220 Ω
R4 …………… 220 Ω
C1 …………… 47 uF electrolytic
C2 …………… 47 uF electrolytic
C3 …………… 47 uF electrolytic
DL1 …………. LED
DL2 …………. LED
IC1 ………….. integrated SN74HC132
IC2 ………….. integrated MC78L05
S1 …………… switch
(Unless otherwise noted, all resistors are 1/4 W 5%

The pin 3 (non-inverting) of the operational amplifier IC1 is connected to the junction of the LDR and R1 trimmer. The LDR being connected to + 12 volts and the trimmer to ground, together form a bridge with a variable value. The opposite pin (inverting) of the operational amplifier is connected to the junction of two resistors R2 and R3, R2 being connected to + 12 volts and R3 to ground, together form the fixed bridge. Voltage at the output of operational amplifier is 6 volts. When the LDR is illuminated by light, at pin 3 of IC1, we have a positive voltage is higher than that present at pin 2and therefore the output pin 6 of IC1 is at logic 1 (at + 12 volts).

The resistor R4 therefore can not biasing the transistor which isa PNP, relay remains inactive. When the LDR is placed in the dark, the pin 3 of IC1 has a lesspositive voltage on pin 2. Therefore, the output pin 6 of IC1 is at logic level 0 (ground). The resistor R4 is grounded and the base of transistor TR1 is biased (PNP).  The latter then becomes conductive and the relay placed in the collector is activated. which used to control any load. The trimmer R1 connected in series with the photoresistor used for test the detection sensitivity.

Parts list :
R1 ………. 10 k trimmer
R2 ………. 10 k
R3 ………. 10 k
R4 ………. 1.2 kOhms
R5 ………. 1.2 kOhms
FR1 ……… photoresistor
C1 ………. 100 uF electr olytique
DS1 …….. 1N4007 diode
TR1 ……… 2N3702 PNP
IC1 ……… Integrated uA741
RL1 ……… Relay 12 V 1 R

The Rain Alarm circuit applies 4 NAND gates of the 4011 IC. In each individual oscillator, while a single gate is configured a straightforward inverter, some other has one input that will act as a control input. Oscillator action is inhibited if this enter is held low. The first oscillator (IC1a and also IC2b) has this kind of input tied low through a high value resistor (R1) which acts as a sensitivity control. Thus this oscillator will be disabled until the control input is taken high. Any moisture bridging the sensor track will so enable the output which is a square wave at about 10 Hz. This in turn will gate on and off the 500 Hz oscillator formed by IC1c and IC1d. This latter oscillator drives the loudspeaker via R6, the Darlington pair formed by Q1 and Q2, and resistor R7.

This simple LED circuit makes the  LED effect as in Knight Rider LED car. The chain of nine high-brightness LEDs are constantly running from left to right and from right to left. You can use red LEDs, and to attract additional attention to the front – white LEDs.

All types of CMOS chips are used, so it can be powered by a 9V battery PP3, which is enough for a very long time, since the current consumption of the Knight Rider LED circuit quite small.

How its work :
To IC4, C1, R1 and R2 made ​​a pulse generator, which come at terminals 14 of both counters IC2 and IC3.
IC1 – this is a trigger that is used to switch counters IC2 IC3 pin or permit 13.
IC7a valve determines which of the counters have appeared “1″ at the output of Q9 (output 11), ie, which of the counters count up to a maximum value.
IC5, IC6 and protect IC7a output of the counter IC2 and IC3, using the gates, “OR” that feed the anodes of LEDs 1 … 9.

Parts list :
R1,R2 : 10 k ¼
R3 : 470 ohm ¼
C1 : 6.8 uF/16v
IC1 : 4027 one flip-flop
IC2 and IC3 : 4017 two decimal counter
IC4 : 555 timer
IC5, IC6 and IC7 : 4071 three chips gates, “OR”
9 V battery size
high-brightness LEDs
Housing for Knight Rider LED circuit

Based on the book “Gather yourself” no. 2, 2004.

Synthesizer assembly
Before assembling the board review the recommendations that are given at the beginning of this book. To avoid failure, try to observe generally accepted rules of assembly. List of components within the set of NM5101, presented below :

Parts List of NM5101 set

In accordance with Fig. 3 install and weld components on the board. DA1 chip is installed in accordance with Fig. 4 ( Synthesizer lighting effects part 3 ).
After installation check the quality of the ration and proper installation elements. Recheck charge for lack of short-circuits and breaks tracks.

This device would be interesting for students: introduction to the basics of electronics, allowing you to experience the assembly and adjustment of modern electronic devices. Synthesizer will be used for fan of light effects as a festive illumination, or a tutorial on microprocessor technology and programming.
This device requires a voltage 9-25V and current around 50mA.

Description of this Synthesizer

Fig. 1 and Fig. 2 on the Synthesizer lighting effects part 2 shows the assembly of synthesizer boards and electric circuit.

Synthesizer is based on a microcontroller from Atmel (DD1). Power supply of the microcontroller obtained from the IC regulator DA1.
Elements of CI, C2, ZQ1 set the operating frequency of the internal oscillator of the microcontroller. Resistors R1 … R6, R8 – used for current limiting. SW1 button is a consistent choice of animated images. The basic version of the proposed microcontroller 12 stitched images.