A passive crossover is made entirely of passive components, arranged most commonly in a Cauer topology to achieve a Butterworth filter. Passive filters use non-reactive resistors combined with reactive components such as capacitors and inductors. Very high performance passive crossovers are likely to be more expensive than active crossovers since individual components capable of good performance at the high currents and voltages at which speaker systems are driven are hard to make, and expensive. Polypropylene, metalized polyester foil, and paper-electrolytic capacitors are common. Inductors may have air cores, powdered metal cores, ferrite cores, or laminated silicon steel cores, and most are wound with enamelled copper wire. Some passive networks include devices such as fuses, PTC devices, bulbs or circuit breakers to protect the loudspeaker drivers from accidental overpowering. Modern passive crossovers increasingly incorporate equalization networks (e.g., Zobel networks) that compensate for the changes in impedance with frequency inherent in virtually all loudspeakers. The issue is complex, as part of the change in impedance is due to acoustic loading changes across a driver’s passband.

On the negative side, passive networks may be bulky and cause power loss. They are not only frequency specific, but also impedance specific. This prevents interchangeability with speaker systems of different impedances. Ideal crossover filters, including impedance compensation and equalization networks, can be very difficult to design, as the components interact in complex ways. Crossover design expert Siegfried Linkwitz said of them that “the only excuse for passive crossovers is their low cost. Their behavior changes with the signal level dependent dynamics of the drivers. They block the power amplifier from taking maximum control over the voice coil motion. They are a waste of time, if accuracy of reproduction is the goal.”

I find useful pages how to design a passive crossover. Check belo pages:

http://sound.westhost.com/lr-passive.htm

http://www.bcae1.com/xoorder.htm

http://www.termpro.com/articles/xover2.html

Above circuit is an fire alarm circuit which build using a fire alarm sensor component and sound generator component. With simple and cheap component, you can build this circuit for low cost.

The termistor is a fire detector sensor and the NE555 is an audio frequency generator which will resulting the sound of alarm from the speaker.

Source: fire alarm circuit

If you are an electronic hobbyst, you are of course very familiar with this part. This part usually used on PCB, to make the circuit “portable”, easy connect and disconnect to another circuit modul safely without soldering the connector.

A screw terminal is a type of electrical connector where a wire is clamped down to metal by a screw.Screw terminals are commonly used to connect a chassis ground, such as on a record player or surge protector. Most public address systems in buildings also use them for speakers, and sometimes for other outputs and inputs.

One advantage of screw terminals are that no connectors are used, thus no compatibility problems with mismatched sizes or shapes. Additionally, the connections are very secure, both physically and electrically, because they firmly contact a large section of wire. This is also a disadvantage however, because it can take a few minutes to secure or undo a set of connections that could otherwise be simply plugged or unplugged. Another disadvantage is that their use with wire too thin is liable to partly cut through the wire.

Screw connectors sometimes come loose over time if not done up tightly enough at fitting time.

A varicap diode also known as varactor diode, variable capacitance diode, variable reactance diode or tuning diode. Varicap  is a type of diode which has a variable capacitance that is a function of the voltage impressed on its terminals.

Varactor or varicap diodes are used mainly in radio frequency (RF) circuits to be able to provide a capacitance that can be varied by changing a voltage in an electronics circuit. This can be used for tuning circuits including radio frequency oscillators and filters.

They are commonly used in parametric amplifiers, parametric oscillators and voltage-controlled oscillators as part of phase-locked loops and frequency synthesizers.

Varicap Symbol

Varicap Operation

Varactors are operated reverse-biased so no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region thickness is proportional to the square root of the applied voltage; and capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage.

All diodes exhibit this phenomenon to some degree, but specially made varactor diodes exploit the effect to boost the capacitance and variability range achieved – most diode fabrication attempts to achieve the opposite.

Operation of a varicap

In the figure we can see an example of a crossection of a varactor with the depletion layer formed of a p-n-junction. But the depletion layer can also be made of a MOS-diode or a Schottky diode. This is very important in CMOS and MMIC technology.

Component Parts:
R1 = 100K
R2,R5 = 1K
R3,R6 = 470R
R4 = 12K
C1 = 1000µF 25V
D1-D4 = 1N4007
D5 = SCR P0102D
Q1 = BC327
Q2 = BC337
SK1 = Female Mains socket

How it works:
The device formed by Q1, Q2 and related resistors triggers the SCR. The frequency of flashing is provided by R1, R2 and C1. If you want to change the flashing frequency value, you need to  set C1 value. The range is from 100uF to 2200µF, please don’t modify R1 and R2.

The Best performances of this circuit are obtained with C1=470uF or 1000µF and R4=12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops, very small and cheap SCR devices can be used, for example C106D1 or TICP106D.

Source of circuit: redcircuits.com

How the circuit works:
IC1 works to generate 150Hz square wave which having a variable duty-cycle. When potensiometer P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow. Lamp LP1, driven by Q1, is off as the voltage across its leads is too low. When potensiometer P1 is rotated towards R2, the output pulses increase in width, reaching their maximum amplitude when the potentiometer is rotated fully clockwise. In this way the lamp reaches its full brightness.

The lamp LP1 could be one or more 1.5V bulbs wired in parallel. Maximum total output current allowed is about 1A.
R2 limits the output voltage, measured across LP1 leads, to 1.5V. Its actual value is dependent on the total current drawn by the bulb(s) and should be set at full load in order to obtain about 1.5V across the bulb(s) leads when potensiometer P1 is rotated fully clockwise.

Circuit source: redcircuits.com

These Nokia wiring diagram would be help you to fixing your own Nokia cell phone. The files containing almost of Nokia schematic diagrams / circuit diagram.

Visit this page of Nokia cell phone  diagram to download complete Nokia wiring diagram.

Schematic Diagram:

Component Parts:
C1, C2, C3, C4 = 10 – 80pF
C 5 = 10nF
C6 = 1000pF
C7 = 100nF
C8 = 2200mF/35V
L1 1 = coil with diameter of 10 mms, 1 mm
L2 7 = coils with diameter of 10 mms, 0,8 mm
L3 3 = coils with diameter of 10 mms, 1 mm
TR1 = BLY89
RFC = RF tsok
PCB Layout:

30W FM transmiter pcb layout

Circuit characterictics:
Tendency of operation: 18V
Current of Collector: max 3 5th
Gain: max 10dB
Force of Expense: 25-30 W
Output (order C): > 60%

Source: http://www.high-voltage-lab.com/81/linear-fm-30watt
Visit the web for detailed explanation abaout this FM Radio transmiter.

Wiring diagram:

You should look is the color of wires on the wiring diagram, if reversed in the installation of the cable then there will be a short circuit.

Picture above is the wiring diagram for single pole light switch. For the installation of one light that can be controlled from multiple locations, please visit this page.

Spice is an analog circuit simulator which developed at the Electronics Research Laboratory of the University of California, Berkeley by Laurence Nagel. This is an open source software circuit simulator, you may try this software to simulate your circuit.

SPICE (Simulation Program with Integrated Circuit Emphasis) is a general-purpose open source analog electronic circuit simulator. It is a powerful program that is used in IC and board-level design to check the integrity of circuit designs and to predict circuit behavior.

SPICE became popular because it contained the analyses and models needed to design integrated circuits of the time, and was robust enough and fast enough to be practical to use. Precursors to SPICE often had a single purpose: The BIAS program, for example, did simulation of bipolar transistor circuit operating points; the SLIC program did only small-signal analyses. SPICE combined operating point solutions, transient analysis, and various small-signal analyses with the circuit elements and device models needed to successfully simulate many circuits.

Read more about SPICE at wikipedia