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Sunday, October 6, 2013

Battery Discharger Using Discrete Components

The battery discharger published in this website may be improved by adding a Schottky diode (D3). This ensures that a NiCd cell is discharged not to 0.6–0.7 V, but to just under 1 V as recommended by the manufacturers. An additional effect is then that light-emitting diode D2 flashes when the battery connected to the terminals is ﬂat. The circuit in the diagram is based on an astable multivibrator operating at a frequency of about 25 kHz. When transistor T2 conducts, a current flows through inductor L1, whereupon energy is stored in the resulting electromagnetic field. When T2 is cut off, the ﬁeld collapses, whereupon a counter-emf is produced at a level that exceeds the forward voltage (about 1.6 V) of D2.

A current then ﬂows through the diode so that this lights. Diode D1 prevents the current ﬂowing through R4 and C2. This process is halted only when the battery voltage no longer provides a sufficient base potential for the transistors. In the original circuit, this happened at about 0.65 V. The addition of the forward bias of D3 (about 0.3 V), the ﬁnal discharge voltage of the battery is raised to 0.9–1.0 V. Additional resistors R5 and R6 ensure that sufficient current ﬂows through D3. When the battery is discharged to the recommended level, it must be removed from the discharger since, in contrast to the original circuit, a small current continues to ﬂow through D3, R2-R3, and R5-R6 until the battery is totally discharged.

The flashing of D2 when the battery is nearing recommended discharge is caused by the increasing internal resistance of the battery lowering the terminal voltage to below the threshold level. If no current ﬂows, the internal resistance is of no consequence since the terminal voltage rises to the threshold voltage by taking some energy from the battery. When the discharge is complete to the recommended level, the LED goes out. It should therefore be noted that the battery is discharged sufficiently when the LED begins to ﬂash.

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Wednesday, April 10, 2013

Basic Components for a Home Theater

Many people never bother looking into purchasing a home theater through sheer fear of the decisions that may need to be made in the process. Many among these aren’t even sure of exactly which components are included in a home theater or which ones are needed in order to create an effective and entertaining home theater. For this reason, many people simply do not bother going through the process of looking at their options when it comes to these wonderful systems on the market today much less ever bother actually purchasing one.

Basic Components for a Home Theater

If you are one of the many who has experienced some degree of confusion when it comes to the individual parts and pieces that are included in a home theater system and what they do, hopefully you will gain a better understanding once you’ve finished reading. The first thing to understand is that there are varying degrees when it comes to home theaters. The following components are the makings of a very basic home theater that will provide excellent functionality. They are not however inclusive of every possible piece or part that could make up a home theater system.

Speaker Setup

Off to the basics, the first thing you’ll need when creating a home theater for your family to enjoy is a television. It might seem a little too obvious to some but I have yet to find a box kit that includes a television—mainly because the choice of screen is for many the most personal aspect of selecting a home theater. There are essentially three choices in today’s television market: front projector, rear projector, and plasma. There are variations within each of these and the prices fall anywhere from modest to quite costly. This is the component that most home theater owners spend the most time contemplating and it affects the types of components that will be most effective later on in terms of things such as high definition and other choices you can make.

A receiver is another important component. You will probably have a DVD player or recorder of some sort as part of your system; you may have a Tivo and cable box or satellite and will probably have speakers of some sort for your system. The receiver is the box you plug them all into—it receives all of this inputs and correlates it so to speak. This is the ultimate traffic director when it comes to your home theater and I suggest you spend a good portion of your home theater budget making sure that this is a good quality part.

Speakers are where your sound will flow. One of the best things to me about a home theater is the ability to experience surround sound very similar to what I experience in theaters while having the ability to put my feet up or snuggle under blankets (which simply can’t be achieved in a theater). Speakers come in all shapes and sizes and are also quite personal for some consumers while give and take for others. You can purchase these are part of a kit in order to make the selection process easier.

Finally, you have your DVD player or recorder. If high definition is important to you, you now have that option. If your television isn’t HD ready or capable, I’d pass and go for an older (less expensive) model of DVD player until something more up-to-date is called for. These items are a great start for any home theater and you can build, expand, and upgrade over time for an even better system. Enjoy!

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Related Circuit : Make 5.1 channel amplifier and speaker setup

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