Showing posts with label make. Show all posts
Showing posts with label make. Show all posts
Wednesday, July 10, 2013
Make an Efficient LED Emergency Light Circuit
The article describes a very simple homemade emergency light circuit that can be used during power failures and outdoors where any other source of power might be unavailable. The circuit uses LEDs instead of incandescent lamp, thus making the unit very power efficient and brighter with its light output. Moreover, the circuit employs a very innovative concept especially devised by me which further enhances the economical feature of the unit.
We know that LEDs require a certain fixed forward voltage drop to become illuminated and it is at this rating when the LED is at it’s best, that is voltages which is around its forward voltage drop facilitates the device to operate in the most efficient way.
As this voltage is increased, the LED starts drawing more current, rather dissipating extra current by getting heated up itself and also through the resistor which also gets heated up in the process of limiting the extra current.
If we could maintain a voltage around an LED near to its rated forward voltage, we could use it more efficiently. That’s exactly what I have tried to fix in the circuit.
Since the battery used here is a 6 volt battery, means this source is a bit higher than the forward voltage of the LEDs used here, which amounts to 3.5 volts. The extra 2.5 volts rise can cause considerable dissipation and loss of power through heat generation.
Therefore I employed a few diodes in series with the supply and made sure that initially when the battery is fully charged; three diodes are effectively switched so as to drop the excess 2.5 volts across the white LEDs (because each diode drop 0.6 volts across itself).
Now as the voltage of the battery drops, the diodes series are reduced to two and subsequently to one making sure only the desired amount of voltage reaches the LED bank.
In this way the proposed emergency lamp circuit is made highly efficient with its current consumption, and it provides backup for a much longer period of time than what it would do with ordinary connections.
Tuesday, April 2, 2013
Using Current Source to Make Linear Scale Analog Ohm Meter
Many analog ohm meters have non linear scale, so the resolution become worse at higher resistance value. This because they use cheap current source, only a series resistance to approximate an ideal current source. An ideal current source will force a consistent current amount regardless of the tested resistor value. Using regulated current source, the current flowing through the tested resistor will be kept constant, so the measured voltage across the tested resistor is proportional (linear) to its resistance value. This is the figure of the circuit.
The current source is provided by IC1a. The two 1N4148 diodes give a constant reference, so the voltage across selected R2..R6 is constant at about 1.4 volt. The R1..R6 is selected to measure different resistor ranges. The VR1 has to be adjusted every time you switch for different range, just like as you do in your old classic analog ohmmeter.
Friday, March 22, 2013
Make this Li Ion Battery Charger Circuit
It is generally advised that a Li-ion battery should be charged with utmost care and caution as these type of batteries are prone to instant damages or explosions if the specified charging measures are not employed. Here we discus a Li-ion charger circuit which has been specifically designed for charging all types Li-Ion Batteries very safely and without any considerations.
Thanks to TEXAS INSTRUMENTS for providing us with this wonderful chip, the LM3622 which is an excellent Li-Ion charger, controller device. The IC has been designed for generating a constant current at constant voltage, a basic prerequisite for all Li-Ion batteries. The IC may be configured for charging a single Li-Ion cell or a pack of many.
The circuit using the IC LM3622 can be fed with voltages right from 5 to 24V depending upon the charging needs and the connected battery. The IC does not require any precision external resistors for implementing the functions. Moreover, the IC has a negligible drain of less than 200nA of current from the battery in the absence of an input voltage.
The in built circuitry of the chip accurately regulates the charging current through the principle of temperature compensated band-gap reference. The current is regulated, however its done via an external current sensing resistor.
The band gap principle results in an efficient operating control performance of the circuit and also of the input supply voltage.
The circuit diagram illustrates a low drop out linear Li-Ion battery charger design which is capable of charging a single 3.7V Li-Ion Cell.
For enabling low voltage detection, the switches J1 and J2 may be appropriately selected.
The IC starts the charging process by first detecting the voltage of the cell and “enable status” of the low voltage detection.
The transistor Q2 immediately comes into the operating condition as soon as the connected battery hits target regulation level, determined by the internal setting of the IC.
Q2 now begins supplying a regulated voltage to the connected battery, initiating a constant voltage charging mode of the circuit.
In the above situation the battery receives a constant regulated voltage across its terminals, while the charging current is monitored depending upon the level of charge over the battery.
On reaching a full charge condition, the charge current to the battery is significantly reduced to a safe value.
For more information, you may refer to the following article.
Make Interesting Flasher and Fader LED Circuits Using IC 555
The astable multivibrator mode is the most fundamental mode of operation of the IC 555. In this mode it basically functions like a free running oscillator. If this oscillator rate is reduced sufficiently, can be used for driving LED lights.
The wiring at the output can also be further modified for achieving interesting variations and light illumination patterns over the connected LED. Some of the practical ways of this is explained here, circuits diagrams of LED flasher, ghost effect generator, alternate blinker, light fader etc are also included.
The article explains a few interesting and simple LED blinker circuit configurations using the ubiquitous IC 555. The basic flashing mode has been kept intact yet various different attributions are provided to the circuit with its flashing rate and pattern.
The IC 555 is a complete package for the hobbyists. You can build numerous interesting circuits with this chip and make it to work as virtually any way you desire. Though the circuit provides us with many application ranges, flashers configurations are more commonly associated with these chips. These can be made to blink all types of lights at different rates depending upon individual preferences. You can flash LEDs, torch bulbs, string lights or even mains AC lamps with circuits incorporating this IC.
Basically, to configure the IC as a flasher or blinker, it’s connected with its fundamental astable mutivibrator mode. This configuration in fact requires just a couple of resistors and a couple capacitors to kick start the said functions. Once the chip is assembled as an astable, we can go ahead and enhance the output in many different ways to get outstanding visual treats.
Let’s learn how a few fabulous IC 555 circuits with LED can be built with the following discussions, but first we would like to know what materials are needed for this.
Being a hobbyist you would want to have a bunch of assorted resistors in your box of goodies and also some selected values of capacitors. For the present projects you would require a handful of different value resistors and capacitors.
Parts List
Resistors rated at ¼ watt, 5 %, unless otherwise stated.
Resistors – 1 K, 10 K, 680 Ohms, 4.7 K, 100 Ohms, 820 Ohms, 1 M etc.
Capacitor – 0.01 uF, 470 uF, 220 uF, 1 uF
Zener diode – 5.1 volts, 400 mW
LED – Red, Green, Yellow 5mm
Circuit Ideas
The first figure shows the basic configuration associated with 555 ICs, here it is connected as an astable multivibrator. The resistors and the capacitor 1 uF can be experimented with to get different rates of blinking over the connected LED. The LEDs can also be used with oter colors.
The 1 K resistor can be replaced with lower values for increasing the intensity of the LED, however it should not be redced below 330 Ohms.
Alternatively the 1 M resistor can be interchanged with a pot for attributing the circuit with variable blinking rate feature.
Making a Police Revolving Light Effect
The above circuit can be suitably modified for producing a revolving, flashing police light effect to the above constructed circuit. Here by adding a network of a zener diode / resistor / capacitor, to the output of the circuit, just as shown in the figure, we can acquire a very peculiar effect with the generated illuminations of the LED. The LED initially glows bright, then slowly dies down, but intermittently gives a high intensity pulse producing the discussed police warning roof light indicator illusion.
Random Light Effect Generator
The configuration shown in this figure enables us to use the circuit to generate random light patterns over the connected group of LEDs. As shown, three LEDs are connected in conjunction with a couple of resistors and a capacitor. The two LEDs connected in parallel but with opposite polarity, flasg alternately at a particular rhythm while the third LED fluctuates at some other random rate.
The above effect can be simplified by the circuit shown below. Here, the LED which is connected to the 1 K resistor blinks at the fixed blinking rate, but the next LED which is connected to the ground switches rapidly at some other defined rate.
Adding a Spooky Effect to the LED
If you want to produce some strange illumination pattern over the LED discussed through the above circuits, them it can be simply done using just a couple of resistors at the output of the IC. As can be seen in the figure, two resistors and a single resistor are connected at the output of the IC in a special way. The network switches ON the LED sharply, but switches it OFF slowly, producing quite a creepy visual effect.
Alternate Blinker
This configuration is pretty straightforward, as we all know; two LEDs can be connected to the IC output for generating an alternate blinking pattern over the connected LEDs.
The above circuit can be further modified as shown below by complely disarranging the network with the shown type. Here the LEDs though blink alternately, the intensity may fluctuate from dim to bright over the LEDs.
Light Fader Circuit Using IC 555
A very interesting light fading effect can be achieved by wiring up the IC 555 circuit as per the diagram shown below. The circuit switches ON the LED very gradually and does the same while switching it OFF, that is instead of shutting it off abruptly, does it very slowly.
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