Showing posts with label 555. Show all posts
Showing posts with label 555. Show all posts
Wednesday, September 4, 2013
Simple Metal Detector Using 555 Timer
This metal detector electronic project schematic circuit is designed using a simple 555 timer integrated circuit . As you can see in the schematic circuit , this metal detector electronic project requires few external electronic parts . This circuit detects metal and also magnets.
Metal Detector with 555 Timer Circuit Daigram
When a magnet is brought close to the 10mH choke, the output frequency changes. This metal detector project can be powered from a power supply that can provide an output DC voltage between 6 an 12 volt . If a metal is closer to the L1 coil , will produce a change of output oscillation frequency, that will generate a sound in the 8 ohms speaker
Metal Detector with 555 Timer Circuit Daigram
Wednesday, April 3, 2013
Photo Switch Circuit using 555 IC
Here’s a design circuit for simple photo switch suitable for home and industrial purpose. The circuit switches on a relay when the light intensity falling on the sensor crosses the set limit. The circuit is based on a NE 555 and two transistors for driving the relay. The resistor R1 is adjusted such a way that under normal condition the voltage across the LDR is less than 1/3 the supply voltage. In this condition output of IC is high.
This makes transistor Q1 on. Transistor Q2′s base is connected to collector of Q1. So Q2 will be off keeping the relay de energized. When light falls the voltage across LDR rises above 2/3 Vcc. This makes the output of IC go high making the relay to energized. The result we get a relay that operates according to the intensity of light falling on the LDR. To setup the circuit switch on power supply, connect a multi meter across LDR and adjust R1 so that voltage across LDR is just below 1/3 supply voltage. Ensure that relay is off in this condition. If not reduce voltage across LDR further more by adjusting R1 to make relay off.
Now cover the top of LDR using a black paper and see the relay gets activated. If not, make further adjustments with R1.Nothing to care after some trial and error you will get the correct set point of R1 where the circuit works. This circuit is nothing great, but some simple basics. I have tested this and got good results. So no problem .Just proceed. If there is some chattering in the relay , that may be because off the difference between the turning on and turning off voltages. This can be avoided by connecting a resistor whose value is equal to 1/2 the resistance of LDR at illuminated condition.
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This makes transistor Q1 on. Transistor Q2′s base is connected to collector of Q1. So Q2 will be off keeping the relay de energized. When light falls the voltage across LDR rises above 2/3 Vcc. This makes the output of IC go high making the relay to energized. The result we get a relay that operates according to the intensity of light falling on the LDR. To setup the circuit switch on power supply, connect a multi meter across LDR and adjust R1 so that voltage across LDR is just below 1/3 supply voltage. Ensure that relay is off in this condition. If not reduce voltage across LDR further more by adjusting R1 to make relay off.
Now cover the top of LDR using a black paper and see the relay gets activated. If not, make further adjustments with R1.Nothing to care after some trial and error you will get the correct set point of R1 where the circuit works. This circuit is nothing great, but some simple basics. I have tested this and got good results. So no problem .Just proceed. If there is some chattering in the relay , that may be because off the difference between the turning on and turning off voltages. This can be avoided by connecting a resistor whose value is equal to 1/2 the resistance of LDR at illuminated condition.
Saturday, March 30, 2013
Wide Frequency Range 555 VCO
The 555 frequency can be varied via adjusting the voltage at pin 5. However, the range and linearity of frequency adjustment is very limited. This is a way to greatly improve performance using the inverted 555 timer circuit that was previously posted.
Current source
Q2 is connected in the common base configuration. In this mode of operation, the collector current is a function of emitter current regardless of the collector voltage. In this way, it can perform a linear charge function upon C1. The emitter must be driven from a negative supply voltage. Frequency is scaled to 10V = 10kHZ via R5. Frequency range in this set-up is 180 to 10kHZ.
Bias transistor
Q3 is wired as a self-biasing transistor by connecting the base to the collector and feeding it a bias current via R4. Voltage drop is 0.6V. Originally, I had a 1N4148 diode and its voltage drop was 0.45V that added too much offset to the emitter of Q1. Ideally, the voltage drop across Q3 should equal Vbe of Q2. This is a compromise because they are matched only under the condition of Ie = (9V – 0.6V) /R4 = 84uA. The emitter current varies from about 3 to 303uA.
Lowest low end offset would occur with both transistors matched and R4 increased to 3M—in that case, the hFE @ 3uA must >100—this looks practical, but would require a different transistor selection—I did not experiment with this option.
Reset transistor
Q1 is a 2N4401. It varies from the 2N3904 in that its current gain (hFE) is optimized at a higher current. The reset current must be high due to its low duty cycle.
Oscillographs
Linearity
Linearity is shown over two orders of magnitude. While not perfect, it shows how the circuit performs. The error on the low end is caused by input offset voltage that is not perfectly nulled via the voltage drop of Q3. On the high end, non-linearity is caused by the finite reset time of the 555 that runs about 6% @ 10kHZ.
Spread sheet data
There is some extra stuff here to generate a -10V reference from a single 19V supply.
Disadvantages
Frequency is a function of Vcc—requires stable supply
High component count
Requires negative reference voltage—no issue if already using split supply
Conclusion
I do not generally recommend this circuit, but believe that it would make a great lab experiment for those who really want to learn more about VCO’s and the versatile 555.
For the future
XR4151 VCO circuit
Charge pump VCO circuit
Preferred components for the serious experimenter
2N4401, 600mA, 60V, hFE = 100 @ 150mA
Digikey 2N4401-ND
$0.20 each
EBC pinout
2N3904, 200mA, 60V, hFE = 100 @ 10mA,
Digikey 2N3904FS-ND
$0.18 each
EBC pinout
readmore...
555 VCO Schematic
Current source
Q2 is connected in the common base configuration. In this mode of operation, the collector current is a function of emitter current regardless of the collector voltage. In this way, it can perform a linear charge function upon C1. The emitter must be driven from a negative supply voltage. Frequency is scaled to 10V = 10kHZ via R5. Frequency range in this set-up is 180 to 10kHZ.
Bias transistor
Q3 is wired as a self-biasing transistor by connecting the base to the collector and feeding it a bias current via R4. Voltage drop is 0.6V. Originally, I had a 1N4148 diode and its voltage drop was 0.45V that added too much offset to the emitter of Q1. Ideally, the voltage drop across Q3 should equal Vbe of Q2. This is a compromise because they are matched only under the condition of Ie = (9V – 0.6V) /R4 = 84uA. The emitter current varies from about 3 to 303uA.
Lowest low end offset would occur with both transistors matched and R4 increased to 3M—in that case, the hFE @ 3uA must >100—this looks practical, but would require a different transistor selection—I did not experiment with this option.
Reset transistor
Q1 is a 2N4401. It varies from the 2N3904 in that its current gain (hFE) is optimized at a higher current. The reset current must be high due to its low duty cycle.
Oscillographs
Spread sheet data
link to wide range 555 VCO.xls
Protoboard setupThere is some extra stuff here to generate a -10V reference from a single 19V supply.
Disadvantages
Frequency is a function of Vcc—requires stable supply
High component count
Requires negative reference voltage—no issue if already using split supply
Conclusion
I do not generally recommend this circuit, but believe that it would make a great lab experiment for those who really want to learn more about VCO’s and the versatile 555.
For the future
XR4151 VCO circuit
Charge pump VCO circuit
Preferred components for the serious experimenter
2N4401, 600mA, 60V, hFE = 100 @ 150mA
Digikey 2N4401-ND
$0.20 each
EBC pinout
2N4401 datasheet
2N3904, 200mA, 60V, hFE = 100 @ 10mA,
Digikey 2N3904FS-ND
$0.18 each
EBC pinout
2N3904 datasheet
555 datasheet
Friday, March 22, 2013
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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