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Three types of systems have been used in modern times:

	The Breaker Point System
	The Electronic System
	The Computerized System
	The Distributorless System

We will discuss them all, but the one we will deal with in the greatest detail, is the breaker point system. The way they create the high voltage spark is the same in all types of systems, the only thing that differs is the way they are controlled.

All ignition systems have two circuits;

The Primary Circuit

The primary circuit is the low voltage circuit that controls the ignition system.

The primary circuit consists of:

	Battery – provides the power to run the system.
	Ignition Switch – allows the driver to turn the system on and off.
	Ballast Resistor – reduces battery voltage from 12 volts to 9 volts.
	Points – a mechanical switch that acts as the triggering mechanism.
	Condenser – protects the points from burning out.
	Primary Coil – produces the magnetic field which creates the high voltage in the secondary coil.
	Wires – join all the components together.

The Secondary Circuit

The secondary circuit is the circuit which converts magnetic induction into high voltage electricity to jump across the spark plug gap, firing the mixture at the right time.

The Secondary Circuit consists of:

	Secondary Coil – the part of the coil that creates the high voltage electricity.
	Coil Wire – a highly insulated wire, that takes the high voltage from the coil, to the distributor cap.
	Distributor Cap – a plastic cap which goes on top of the distributor, to hold the high tension wires in the right order.
	Rotor – spins around on the top of the distributor shaft, and distributes the spark to the right spark plug.
	Spark Plug Wires – another highly insulated wire that takes the high voltage from the cap to the plugs.
	Spark Plugs – take the electricity from the wires, and give it an air gap in the combustion chamber to jump across, to light the mixture.

Electrical Terms and Principles

Terms;

1. A Circuit is the continuous path that the electricity goes through. It must be complete from the source, to the switch, to the load, and back to the source again.

2. Ground is the part of the circuit which is not wires, but a part of the car’s metal body. This is almost always the negative side of the battery.

3. Voltage is the electrical pressure that makes electrons move through a wire. High voltage requires lots of insulation to prevent electrons leaking to ground. An example of a high voltage circuit, is the secondary circuit. Voltage is measured in volts. An ignition system can produce as much as 45,000 volts, a battery, 12 volts.

4. Current is the actual amount of electrons flowing. Large amounts of current require lots of copper to travel through. An example of a circuit with a large amount of current, is the cables from the battery to the starter. Current is measured in amperes, or amps for short. A starter can draw 200 amps, an ignition system, less than 5 amps.

5. Resistance is the opposition to current flow, and is measured in ohms.

6. Magnetic Field can best be described by imaginary lines of force between one pole of the magnet and the other.

Principles

1. When electricity flows through a wire, a magnetic field is built up around the wire.

2. When a wire passes through magnetic lines of force, cutting them, a voltage is induced in the wire.

3. Three things are needed to produce electricity:
1. Magnetic Field
2. Circuit – a path for the electricity to go through.
3. Motion – either the wire, or the magnetic field, has to move.  

…So, How Does The Ignition System Work Anyway?        

Electrons, supplied by the battery when the engine is starting, or by the alternator when the engine is running, are supplied to the primary circuit at about 12 volts electrical pressure. When the circuit is completed by turning on the ignition switch, and the breaker points are closed, those electrons flow through the primary coil, across the points to ground, and back to the battery again.

When electrons flow through a wire, a magnetic field is built up around the wire. Make the wire into a coil, and the magnetic field increases by the number of loops in the coil. This magnetic field takes a relatively long period of time to build up. It isn’t instantaneous. The time the coil is charging up is called coil saturation, and is controlled by the amount of time the breaker points are closed, or “dwell”. the longer the points are closed for, the longer the dwell, and the stronger the magnetic field becomes.

The coil is actually named wrong. It shouldn’t be called the coil. It should be called the “coilS”. The primary coil is the one that builds up the magnetic field. It has a few hundred turns of relatively large wire in it.. The secondary coil has a few thousand turns of small diameter wire in it because it is the one that will make the high voltage, but low current, and fire the spark plugs. 

So when the points are closed and the ignition switch is turned on, a magnetic field is built up around the coil. When the points are opened by the distributor cam, electrons can no longer flow, so the magnetic field collapses toward the center of the coil at the speed of light. When it collapses, it moves through the secondary coil.  Since the secondary coil has so many turns of wire, and the speed of the magnetic field is so high, a great deal of voltage is induced into it. 

Not all of the electrical energy is actually used though. Voltage only builds up until there is enough to ionize the air in the gap between the positive and ground electrodes of the spark plug. When there is enough voltage the spark plug fires and releases the energy to ground. It will always take between 5,000 (5KV) and 15,000 (15KV) volts to jump across the spark plug gap. If it takes more, there is too much resistance in the plug circuit, or there is too wide a spark plug gap. If it takes less than 5KV to fire the plug, there is a short, caused by a shorted plug wire, too small a spark plug gap, or a fouled plug.

The high voltage electricity produced in the secondary coil goes from the coil tower, through the coil high tension wire to the distributor cap, from the center of the cap across the rotor to the outer terminal of the cap, through the spark plug high tension wire to the spark plug, across the plug gap to ground firing the mixture in the combustion chamber. This all takes place at the speed of light.

The coil is actually a transformer. It transforms a twelve volts or so, into as much as 45,000 volts.

	A breaker point ignition system is capable of producing between 20,000 and 30,000 volts of electrical pressure. There is very little actual current flow.
	Electronic ignition systems were first used as standard equipment in 1975 because of the 50,000 mile emission durability test required by the Environmental Protection Agency. The problem with the old system which had been used for seventy five years, was the points, which started to deteriorate after 1,000 miles, and were totally worn out by 20,000 miles. An electronic ignition system uses a transistor to turn on and off primary power. Transistors are electronic switches that either work or don’t, they don’t just deteriorate in use. Electronic systems are capable of producing up to 45,000 volts and much higher amounts of current than the breaker point system.
	The spark will take place just before Top Dead Center on the compression stroke.

Parts of the Primary Circuit

Points

The points are not anything mysterious. they are simply a mechanical switch that turns on and off the ignition coil. The are opened by the distributor cam, and closed by the point spring. When they are closed, the electricity flows from the battery to the ignition switch on the steering column, to the positive side of the primary coil, and across the points to ground. The only way the electricity can get to ground is across the points, so when the points open, electrons can no longer flow and the magnetic field around the coil collapses.

The points are the weak link in an ignition system that includes them. After as little as 1000 miles they have deteriorated significantly, and gone out of adjustment. By 20,000 miles the engine is not likely to run at all.

The points must be replaced, and adjusted at the time of a tune-up. They are set by adjusting “dwell, which is the number of degrees of distributor cam rotation the points are closed for. Dwell, coil saturation time, and cam angle are all the same thing.

As you can see in the diagram, the closer the points are to being closed, the longer they stay closed for and therefore the longer Dwell is. To adjust the points, simply hook up a dwell meter to the coil. ( red lead to negative, black to engine ground) Crank the engine with the distributor cap and rotor off, and adjust the fixed contact of the points until the correct dwell reading is obtained. 

If there is a range in the dwell specification, adjust the points to the low end of the range because dwell will always increase as the rubbing block wears down.

Condenser

The sole purpose of the condenser is to protect the points, and keep them from burning out prematurely.

The collapsing magnetic field not only collapses through the secondary coil, but also through the primary coil. The collapsing field induces a few hundred volts in the primary coil. These electrons have to go somewhere,  they are just trying to get to ground by the easiest means possible. If they were allowed to jump across the points, they would burn them out in as little as 100miles. They see the condenser as an easy way to ground but what it really does is store them for a fraction of a second. Meanwhile the points have opened far enough that the 300 volts or so, can’t jump across them.

The condenser is just a little can with a strip of tin foil and a strip of waxed paper, rolled together inside a little can. A wire is attached to the roll of tin foil and the waxed paper is there to separate one roll of the foil from the next one. The condenser is merely a storage room for electrons.

Ballast Resistor (or resistor wire)

The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to
9 volts by the Ballast Resistor. When the ignition switch is in the “run” position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to “start”, the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time.

Battery

Don’t forget, without a good battery, you don’t have a good ignition system.

Primary Coil

The primary coil has a few hundred turns of relatively large wire. Its positive side is connected to the ballast resistor, and its negative side is connected to the distributor (or the module in an electronic system). The primary coil is the one that builds the magnetic field around it.

Parts of the Secondary Circuit

All parts of the Secondary circuit are highly insulated to prevent the high voltage electricity from escaping to ground.

Secondary coil

The secondary coil has a few thousand turns of hair fine wire. It is the coil that the magnetic field moves through to produce the high voltage electricity. Because of the high number of turns of wire, and because of the extremely high speed the magnetic field is moving at, ( the speed of light ) extremely high voltage is produced, but because the current flow is very small, the wire only needs to be small too. The positive side of the secondary coil attaches to the positive primary wire, and the negative side goes to the coil tower where the coil high tension wire plugs in.

Rotor

The rotor spins around on the top of the distributor shaft and distributes the spark from the center terminal of the cap to each insert around the outside in the firing order. Is snaps onto, or is held by screws, to the top of the distributor shaft, and only goes on one way.
The rotor is made of “Bakelite”, a type of plastic. Bakelite differs from most plastics in that is is capable of withstanding a fair amount of heat. It is, however, quite brittle, but it does have high dialectic strength or resistance to current flow.

During a tune-up, the rotor should be checked for worn electrodes, cracks, and evidence of punctures. These are places where the electricity has burned through the rotor to the distributor shaft.

Distributor Cap

The distributor cap is also made of bakelite. It has brass, copper, or aluminum inserts in it to conduct the electricity to and from the rotor and the high tension wires. The cap usually has ribs on the inside to prevent flashover between the terminals. There is one insert in the center for the coil HT wire, and inserts around the outside for the spark plug HT wires. The plug wires are pushed into these terminals in the firing order.
Good quality caps have copper or brass inserts and not aluminum. There is arcing between the cap and rotor and that arcing causes oxidation of the inserts. Aluminum oxide is a very effective abrasive and causes wear on the distributor shaft bearings.

	During the tune-up, the cap should be checked for any wear on the inserts, and evidence of “carbon tracking”. These are places where the electricity has made another way to ground, or one of the other terminals in the cap.
	Both cap and rotor should be checked during a tune-up, but they don’t necessarily have to be replaced unless they show wear.

High Tension Wires

The HT leads are highly insulated to prevent the electricity taking a short circuit to ground. There are usually one plug wire going to each spark plug, and one coil wire going from the coil to the center of the cap, although on GM’s High Energy ignition system the coil wire has been eliminated by placing the coil directly on the top of the cap.
Ht leads are usually carbon core; very much like a little piece of string impregnated with graphite. There is very rarely an actual conductor made of copper. The insulation makes up a large percentage of the diameter of the wire, and is usually made of silicon in modern wire sets.

	During the tune-up the wires should be checked for evidence of burn through, deterioration of the wire, or boots, or any abnormality.
	The plug wires should be separated from each other, and never bundled together. Bundling the wires causes cross-fire between the plug leads and therefore the spark plugs.
	The plug wires can be checked on an engine analyzer, or oscilloscope for high or low firing lines. High firing lines indicate open circuits caused by a broken wire or spark plug, or a wide spark plug gap. Low firing lines indicate a short , caused by leakage to ground. This could be a wire laying across an exhaust manifold or the cylinder head. If you don’t have an oscilloscope, HT leads can be checked with an ohm-meter. There should be about a thousand ohms of resistance per foot of wire.
	When pulling plug wires off the spark plugs, twist and pull the boot, don’t yank on the wire itself. This will cause the wire to break inside and although it will still work right then, it will give problems down the road as the wire burns back in both directions from the break.
	Wire sets don’t necessarily have to be replaced during a tune-up, but they should always be checked.

Spark Plugs

The spark plugs are the last remaining part of a modern ignition system that need servicing on a regular basis. 

The plugs must have the correct “reach”, or length of the threads, diameter, sealing method, and heat range. 

The plug on the left  requires the use of a seal ring, or gasket to prevent compression leakage past the threads. The plug on the right does not require a gasket.

The spark plug must run at the correct temperature. If the plug runs too hot, above 900 degrees Celsius, it will glow red hot, and the fuel mixture will start on fire all by itself, not when the plug fires. This is called pre-ignition, and must be avoided at all costs. If the plug runs too cool, below 450 degrees Celsius, it will foul up with crud because it never cleans itself. High performance and high compression engines have a great deal of heat in the combustion chamber (remember, its the heat that pushes the pistons down) and so don’t require any “artificial” heat created by the plug to keep it hot. High performance engines use cold plugs. Low performance, low compression engines don’t have a great deal of heat in their combustion chambers and therefore need to keep the plugs hot in another way. They use hot spark plugs.

Note the short heat path in the plug on the left. Remember, the hottest part of the plug is the center electrode. The shorter the distance the heat has to travel to the coolant, the cooler the plug runs. A hot spark plug has a longer insulator nose.

Projected nose or extended tip plugs take the whole insulator and move it further out into the combustion chamber. This moves the tip into the swirling gasses in the combustion chamber and the tip keeps cleaner than a normal plug and prevents fouling.

A technician can tell a great deal about the engine he is working on simply by “reading” the spark plugs

Worn plugs, like the one on the right in the drawing above, should be replaced.

	The spark plug air gap must be set when the plugs are installed.
	Spark plugs are not normally cleaned and re-gapped anymore. Sand blasting the insulator gives it a rough finish and it fouls up easier than when new.

Timing

To give the maximum cylinder pressure and therefore the maximum horsepower, burning of the gasses must be finished by shortly after Top Dead Center. If the piston is allowed to go too far down the cylinder, the combustion chamber volume will have become too big, the pressure will drop and so will the power and economy.
In a breaker point ignition system, point opening triggers when the spark happens, so by changing where the points open in relation to the distributor cam, we change when the spark happens. The same thing happens in an electronic system when the transistor turns the coil off. Timing very rarely needs adjusting in an electronic system because there is nothing that goes out of adjustment. If timing is off, then someone probably adjusted it wrong last time.

Basic or Initial Timing

Basic timing is the starting point for the automatic timing advance systems so it is imperative that it be set correctly. 

To set the timing:

	The engine must be at idle speed to make sure mechanical advance isn’t operating.
	The vacuum line to the distributor vacuum chamber must be disconnected to make sure vacuum advance isn’t operating.
	Basic timing is set by moving the distributor body which of course has the points attached to it. Loosen the clamp that holds the distributor down so the distributor can be moved but leave it tight enough that it can’t move itself. Attach a timing light to the engine and shine it down at the timing marks. The timing light will “freeze” the timing mark on the balancer whenever #1 spark plug fires. Adjust the distributor body so the timing mark on the balancer lines up with the correct mark on the scale, and tighten down the distributor clamp. Timing marks can also be located on the engine’s flywheel, especially in front wheel drive cars.

If basic , or initial timing is wrong; both vacuum and centrifugal advance will be off too.

Centrifugal Advance

Centrifugal advance affects power.

The fuel in the combustion chamber takes approximately the same amount of time to burn no matter what speed the engine is running at for equal throttle opening. Remember that the spark only starts the fuel burning. Once we have lit it on fire with the spark, it keeps burning all by itself, and that takes time. It takes time for the flame to travel across the cylinder. At low RPM, the piston doesn’t travel very far, and therefore the spark can happen quite late; but as the engine speeds up, the piston is traveling faster, and if the spark does not happen earlier, the piston will have traveled too far down the cylinder, the volume of the cylinder will be too large, pressure will be low, and the engine will be low on power. The spark must be timed earlier to allow for the increased piston speed.

	Notice that at idle, the spark fires at Top Dead Center. The piston only travels 10degrees before the fuel has finished burning.
	At 1000 RPM the spark fires the mixture at 8 degrees before top dead center to have the combustion complete by 10 degrees after TDC.
	At 2000 RPM the spark must fire at 26 degrees before TDC, to have the fuel burned by 10 degrees after TDC.

To do this, small springs hold back advance weights in the distributor, either above or below the breaker plate. As distributor speed increases, these weights are able to overcome the tension of the springs, the weights fly out, and the distributor cam, or timer core advances in relation to the distributor shaft.

Centrifugal advance can be checked very easily, and should always be checked during a tune-up. When you’ve got a timing light on the engine, rev it up a bit, the timing should advance as RPM increases.

Vacuum Advance

Vacuum advance affects fuel economy.

To control the speed of a gasoline engine, a throttle, or butterfly valve is placed somewhere in the air intake system of the engine. When the throttle valve is open, the engine can take in as much air as it wants. When the throttle valve is closed, air supply to the engine is restricted, and this restriction creates a vacuum under the throttle plate called “manifold vacuum”. Wide open throttle, no vacuum. Closed throttle, high vacuum. When the throttle is closed, the amount of fuel and air in the combustion chamber is much less than at wide open throttle, so the molecules of fuel are further apart. Remember, the spark only starts the fuel burning; once it starts burning, it keeps burning all by itself. If the molecules of fuel are further apart, then one has to burn for a slightly longer time before the next one starts on fire, and so on down the line. This makes a difference in the time it takes to burn the fuel. The more wide open (low vacuum) the throttle is, the less time it takes to burn. The more closed the throttle is (high vacuum), the longer the time it takes to burn.

Ported vacuum, taken from above the throttle plate at idle, (you don’t want vacuum advance at idle, it makes the engine hard to start) acts on a vacuum diaphragm, to move the breaker plate that the points are attached to. This advances the timing at part throttle for better fuel economy. 

It is very common for vacuum diaphragms to rupture because of years of being exposed to gas fumes. This causes a sudden decrease in fuel economy.

Vacuum advance can be checked very easily, and should be checked as a part of every tune-up. You don’t need a timing light or anything. With the engine idling, apply a vacuum with w vacuum pump, or by sucking on the vacuum advance line. The engine RPM should change. If it doesn’t change, the vacuum advance diaphragm is ruptured and should be replaced.

Centrifugal, and vacuum advance work together to modify the advance curve of the ignition system to maximize fuel economy, emissions, and power.

Circuit diagram:

Parts:

Device purpose:

This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc and CD players, computers and similar devices having line or headphone output. Of course, in most cases you’ll have to make two boxes to obtain stereo.
The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behaviour and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in transformer. Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies.
In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA.
To measure this current, wire a DC current meter temporarily in series with the collector of Q3.

Technical data:

Output power: 1.5 Watt RMS @ 8 Ohm, 2.5 Watt @ 4 Ohm, 3.5 Watt @ 2 Ohm (1KHz sinewave)

Sensitivity: 100mV input for 1.5W output @ 8 Ohm

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz & 10KHz: Below 0.2% @ 8 Ohm 1W, below 0.3% @ 4 Ohm 2W, below 0.5% @ 2 Ohm 2W.

Note: The text is AUTO translated from Greek version

Cross-over they are netting usually with passive materials that have aim to separate a region of frequencies in smaller. Cross-over the manufacture that to you we offer it separates the acoustic region in two sub areas in order to we lead two loudspeakers for the high frequencies and for low.

Cross-over they are essentially for the operation of combination of loudspeakers. Without them, two things happen: on one side are led all the frequencies simultaneously to different loudspeakers and otherwise is consumed pointlessly force in loudspeakers that cannot him attribute rightly. Cross-over depending on the number of loudspeakers that leads they are distinguished in two streets and three streets, even if they can result also complexes. The each region is figuratively named street, through which will pass the corresponding region of frequencies in order to it leads the corresponding loudspeaker.

The simpler system is that of two streets. In that acoustic region it is separated in two sub areas with two filters: one of low passage and one high. The filter of low passage leads the loudspeaker for the low frequencies and the filter of high frequencies the loudspeaker for the high frequencies. The loudspeaker for the low frequencies is known as woofer and the loudspeaker for the high frequencies as tweeter.

The loudspeakers are distinguished by various characteristics that him make distinguish between them. That characteristics that us interest for the manufacture that we make, are their complex or more simply resistance and diagram that us gives the relation of attribution of sound as for frequency (sensitivity).

The resistance of loudspeakers is characterized in a frequency depending on the destination and their press.  Loudspeakers are distinguished, as for the destination, in loudspeakers of low frequencies, woofer intermediate, mid-range and high tweeter. Their resistance in W is 4W, 8W and 16W. Cross-over that we present it is intended for loudspeakers 8W.

Theoretical Circuit

The theoretical circuit appears in form 1. The manufacture uses passive materials of mediocre dimensions. In order to you make a cross-over you need printed circuit. Observing theoretical circuit we see that it has a entry and two exits, In the entry connect the exit of amplifier and in the exits the loudspeakers. In the one the loudspeaker of high frequencies and in the other the loudspeaker of low frequencies.  The way from the entry to the loudspeaker of high frequencies is not anything other, despite a filter of high frequencies. Respectively, the way to the loudspeaker of low frequencies is a filter of low passage. The filter of low passage consists by inductor L2 and the capacitor C2. The inductor is en line with the circuit and the capacitor at the same time with the loudspeaker.

The complex resistance of this elements changes, associates the price of   frequency. The price of complex resistance of inductor of is proportional frequency and capacitor of reversely proportional frequency. As long as increase the frequency, the self-induction acquires bigger complex resistance and the capacitor smaller. This, in combination with their provision, prevents the high frequencies to reach in the loudspeaker. In the way of high pass filter to the loudspeaker of high frequencies the provision of elements is reversed. En line we place capacitor, a C1 and at the same time inductor L1. In this provision as long as is increased the frequency, is decreased the complex resistance of capacitor while his inductor that is at the same time with the loudspeaker is increased. As long as it increases the frequency, so much facilitates the capacitor the passage of frequencies and so much least it absorbs the inductor force from them.

Apart from the elements of filter in the circuit, existence resistances and capacitors that stabilise the behaviour of loudspeakers. An additional resistance, R3, offers a particular operation. This resistance is always shorts from a safety. If for some reason it passes big current, then is in danger is burned loudspeaker of the high frequencies. Rather the loudspeaker is burned the safety. Then is presented en line the resistance and is decreased the sound level.

Manufacture

In order to you make the manufacture you will need the PCB that appears in form. In this mount materially that exists in the theoretical circuit, according to form.  The montage of materials will begin from the resistances and flowingly will place the capacitors and finally the self-induction. The inductors for the cross-over, if him you find in trade you cans him order from us. In order to you try the cross – over   apply in the exit for the each loudspeaker a resistance 8W. In the entry you will connect a small amplifier with which you will strengthen the signal of acoustic generator. The generator him you will put it produces sine’ signal. Altering the frequency we observe the each expense in an oscillograph. If all have well, then when is increased the frequency and approaches the price 3,5kHz, the tendency in the exit for the loudspeaker of low frequencies falls and the other increases.

Parts

Parts:

Power supply circuit diagram: 

Parts:

Notes:

• Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.

• Q6 & Q7 must have a small U-shaped heatsink.

• Q8 & Q9 must be mounted on heatsink.

• Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter in series with Q8 Drain) with no input signal.

• A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 at output ground. Then connect separately the input and output grounds at power supply ground.

Technical data:

Output power: well in excess of 25Watt RMS @ 8 Ohm (1KHz sinewave)

Sensitivity: 200mV input for 25W output

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz: 0.1W 0.014% 1W 0.006% 10W 0.006% 20W 0.007% 25W 0.01%
Total harmonic distortion @10KHz: 0.1W 0.024% 1W 0.016% 10W 0.02% 20W 0.045% 25W 0.07%

Unconditionally stable on capacitive loads

Make a sound card is no more a complex issue. If you use great IC PCM2702 from BURR BROWN / Texas Instruments you can create a fully functional USB sound card. This sound card can be powered from USB port and has one stereo output. You don�t need to install any driver for Windows XP and Vista, because they are already inside. This is really plug and play.

Few months ago I have seen USB sound card called Alien DAC. The construction on the project web page inspired me to build this thing also.

Description

The core of this construction is 16-Bit Stereo Digital-To-Analog Convertor with USB interface PCM2702.

PCM2702 needs only few additional parts to work. The schematic is not complex. Sound card can be powered directly from USB port (jumper W1) or from external power supply (jumper W3). PCM2702 needs two power supply 3.3V (3V-3.6V) and 5V (4.5V-5.5V). I used fixed output voltage LDO TPS76733Q for 3.3V (IO2) and adjustable output voltage LDO TPS76701Q for 5V (IO3). Both LDO are produced by TI, I used this because I had it in my drawer. Any similar LDO can be used. Output voltage of IO3 should be set to little bit lower than input voltage to allow LDO good stabilization, in my case output voltage is set to 4.8V. Output voltage can be set by adjustable resistor R33. In case of low power supply, IO3 can be shorted by jumper W3. LED D3 signalizes power on.

Assembled top side

Small ferrite beads are placed before all power pins of PCM2702 and in Vbus and GND of USB. These small beads reduce high frequency hum. I had a problem find this small SMD ferrite beads in local stores but finally I acquire few of them from old hard drive. They are not absolutely necessary, you can use zero ohm resistors instead of them.

Low-pass filter is placed in output signal path to reduce sampling frequency. An OPA2353UA dual op amp is configured as a stereo 2nd-order low-pass filter. Led diode D1 is illuminated when PCM2702 plays audio data received from the USB bus. Led diode D2 is illuminated when USB bus suspends audio data transmission to the PCM2702.

Schematic of sound card with PCM2702

PCB

PCB assembly diagram

PCB – Download PCB in [EPS format] or [PDF format]

Bottom side of PCB (single side PCB, made by standard etching method)

Assembled bottom side

Conclusion

This circuit works very well. I only shorted crystal during soldering so the circuit didn�t work, but after removing the short the sound card started to work. I have tested in Windows 2000, XP and Vista. It works in all mentioned systems. Drivers are present in operation system so the sound card is ready in few seconds after you connect it.

During writing this article I have found that PCM2702 is now not recommended for new design, but TI offer even better solution. PCM2704, PCM2705 have same functionality as PCM2702, but they include output filter. They are able to drive directly headphones. Volume and Mute can be controlled through SPI bus in PCM2705 or with pushbuttons in case of PCM2704. PCM2704 and PCM2705 are in TSSOP28 package. PCM2706 is similar to PCM2704 and PCM2707 to PCM2705 but in addition they have I2S bus. PCM2706 and PCM2707 are in TQFP32 package. I recommend using these new chips for new design (look at the TI web page).

]]> http://autoelectronics.wordpress.com/2009/02/09/usb-sound-card-with-pcm2702/feed/ 0 hameedmazhar http://autoelectronics.wordpress.com/2009/02/09/pulse-generator/ http://autoelectronics.wordpress.com/2009/02/09/pulse-generator/#comments Mon, 09 Feb 2009 15:01:09 +0000 hameedmazhar http://autoelectronics.wordpress.com/?p=591 ]]>

Introduction

Pulse Generator kit will generate a frequency in KHz which can form a good test gear project.  This kit is based on the classic LM555 timer IC.

• Input – 12 VDC Max @ 40 mA

• Range – jumper selectable and preset tunable range of 1 Hz to 180 KHz

• Power-On LED indicator

• Terminal pins for easy connection

• Four mounting holes of 3.2 mm each

• PCB dimensions 40 mm x 47 mm

Schematic

Schematic

Layout