Showing posts with label 555. Show all posts
Showing posts with label 555. Show all posts
Basic Theory IC 555
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Theory Timer 555
Timer 555 is a timer IC that works based on the RC circuit and the comparator is coupled with a digital component (R-Sflip-flop). The first 555 of the type manufactured by Signetics SE-555 working at -55 ° C to 125 ° C and the NE-555 working at 0 ° C-70 ° C. Then 555 is produced with different designs include the LM555, 556 (dual version), and LMC-555 (CMOS version). Timer 555 operates at +5 V dc power supply sd +18 V with temperature stability of 50ppm / ° C (0.005% / ° C). Output 555 can be a current sink / source up to 200mA. IC 555 is compatible with the components of TTL, CMOS op-amps, transistors and other types of linear ICs.
Timer 555 can operate either as a monostable or astable. The resulting square wave output can have a variation of duty cycle ranging from 50 - 99.9% and the frequency of less than 0.1 Hz up to more than 100KHz. 555 Series consists of two voltage comparators (COMP1 and COMP2), a control flip-flop RS (reset / set) that can be reset from outside via the pin 4, an inverting amplifier output (A1), and a discharge transistor (Q1). Kompartor second bias level determined by voltage divider resistors (Ra, Rb, and Rc) contained between Vcc and ground. Inverting input 2/3Vcc komparator1 given input and noninverting input from the given input komparator2 1/3Vcc. Monostable operation requires the input pulse triggers the PIN2 of IC 555. Input trigger voltage drop of more than +2 / 3Vcc toward the voltage is less than + Vcc / 3.
Monostable operation Timer 555
Monostable multivibrator (MMV), also called a one shot, producing a pulse output with a certain period when triggered by a pulse input. Output from Oneshot will instantly go high following the trigger pulse (trigger) and will remain high in accordance with its period. When the period had expired, the output will return low. Outpt Oneshot will remain low until there is another trigger. IC 555 can be operated as MMV by adding an appropriate external circuit.
Both internal comparator prasikap given voltage with a certain voltage level by voltage divider arranged series (Ra, Rb, Rc). Inverting input voltage up to 2/3Vcc komparator1 given, and the noninverting input voltage komparator2 given Vcc / 3. Tersebutlah voltage operation resulted in 555 both as a monostable or astable. External timing circuit (R1C1) connected between Vcc and noninverting input komparator1 through pin6. Pin7 also been linked with causing connected as pin6 transistor to the capacitor C1. When the transistor is on, the resistance of the capacitor is so low that connect (short) through the relationship of CE transistor.
When 555 is connected to the source voltage, input voltage inverting komparator1 will receive registration 2/3Vcc and noninverting input voltage komparator2 would have amounted to Vcc / 3. This causes the RS flip-flop in a reset condition, so that its output Qnot high. Therefore flip-flop connected to the output through an inverting amplifier pin3 (A1) then the output 555 low. In these conditions the capacitor charge (charging). Qnot in the high cause transistor Q1 saturated, which means is connected to ground through a capacitor C1. So in this condition the capacitor to remove the charge (discharge) so that Vc = 0.
If PIN2 give trigger input, when pulsatrigger move towards less than 1/3Vcc voltage as shown in the picture, the noninverting input is more positive than the input komparator2 the inverter , so that the output komparator2 be high. At that time, FIP-flop in the set, so that the output Qnot her low and keuaran 555 high. Because of its low Qnot output, means of transistors in the off. Current flows from Vcc to ground through a capacitor C1. In other words, the capacitor re-charging. (Picture). Capacitor voltage will continue to rise until it reaches 2/3Vcc, at which time the output Vc = 2/3Vcc komparator1 be high and cause the flip-flop is reset and the output 555 back to low. The output 555 will remain until there is another trigger input.
All IC timers rely on an external capacitor to determine the interval of time off-on pulse output. The capacitor would require a certain time to charge or discharge through a resistor. Time can be explained and calculated from the resistance and capacity are given. Equation pulse period to 555 depending on the time required by the capacitor at the time of filling until it reaches 2/3Vcc voltage provided by the RC time constant. Thus, if the capacitor voltage e = E (1 - (-t/RC)), can be calculated time will enable the comparator threshold.
555 Timer IC Working Principle
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Block Diagram of 555 timer IC: |
Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high output from the flip-flop saturates the discharge transistor and discharge the capacitor connected externally to pin 7. The complementary signal out of the flip-flop goes to pin 3, the output. The output available at pin 3 is low. These conditions will prevail until comparator 2 triggers the flip-flop. Even if the voltage at the threshold input falls below 2/3 VCC, that is comparator 1 cannot cause the flip-flop to change again. It means that the comparator 1 can only force the flip-flop’s output high.
To change the output of flip-flop to low, the voltage at the trigger input must fall below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its output low. The low output from the flip-flop turns the discharge transistor off and forces the power amplifier to output a high. These conditions will continue independent of the voltage on the trigger input. Comparator 2 can only cause the flip-flop to output low.
From the above discussion it is concluded that for the having low output from the timer 555, the voltage on the threshold input must exceed the control voltage or + 2/3 VCC. They also turn the discharge transistor on. To force the output from the timer high, the voltage on the trigger input must drop below +1/3 VCC. This also turns the discharge transistor off.
A voltage may be applied to the control input to change the levels at which the switching occurs. When not in use, a 0.01 nano Farad capacitor should be connected between pin 5 and ground to prevent noise coupled onto this pin from causing false triggering.
Connecting the reset (pin 4) to a logic low will place a high on the output of flip-flop. The discharge transistor will go on and the power amplifier will output a low. This condition will continue until reset is taken high. This allows synchronization or resetting of the circuit’s operation. When not in use, reset should be tied to +VCC.
LED Flasher Circuit Using 555 Timer IC
This is a simple LED flasher project that uses a common 555 timer IC for its operation. It is configured as an astable mode which means that its output is a square wave oscillator. Two LEDs are connected to its output in such a way that when one LED is ON, the other LED will turn OFF.
It uses only 10 simple parts that are easily available at any electronic shops. Capacitor C2 charges exponentially through resistors R1, R2 and the resistance of the trimpot. When C2 has charged to about 2/3 VCC it stops charging and it discharges to about 1/3 VCC through R2 and the trimpot resistance via pin 7. This is the standard operation of a 555 timer. When a Vcc of 5 V to 15 V DC is applied to the circuit, the LED will start to flash.
The frequency of the flashing can be changed by varying the resistance of the potentiometer or trimpot.Parts List The parts list of the simple LED project is as shown below.
Ramp Generator With 555 Timer IC
Charging current produced by PNP constant current source is
iC = Vcc-VE / RE
where VE = R2 / (R1 + R2) * VCC + VBE
When a trigger starts the monostable multivibrator timer 555 as shown in figure, the PNP current source forces a constant charging into the capacitor C. The voltage across the capacitor is, therefore, a ramp as illustrated in the figure. The slope of the ramp is given as
Latest In Circuit Transistor Checker Using 555 timer
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This simple circuit has helped me out on many occasions. It is able to check transistors, in the circuit, down to 40 ohms across the collector-base or base-emitter junctions. It can also check the output power transistors on amplifier circuits.
Circuit operation is as follows. The 555 timer ( IC1 ) is set up as a 12hz multi vibrator. The output on pin 3 drives the 4027 flip-flop ( IC2). This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LED’s are arranged so that when the polarity across the circuit is one way only one LED will light and when the polarity reverses the other LED will light, therefore when no transistor is connected to the tester the LED’s will alternately flash. The IC2 outputs are also connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will turn on and produce a short across the LED pair. If a good NPN transistor is connected then LED1 will flash by itself and if a good PNP transistor is connected then LED2 will flash by itself. If the transistor is open both LED’s will flash and if the transistor is shorted then neither LED will flash.
From :: http://home.maine.rr.com/randylinscott/nov97.htm
Latest Alternate 555 Oscillator
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This is a slightly simpler circuit than the one above. The circuit uses just one resistor and one capacitor with the 555 timer IC to create a stable and reliable oscillator with an output that it a true squarewave.
The formula for calculating the frequency is:
f=1/(1.4*R*C).
The values in the formula are expressed in ohms, farads, seconds and hertz. This formula is much simpler than that of the previous circuit. With the values shown on the circuit, the frequency is calculated as 1050Hz, but like the previous circuit, this arrangement can operate at frequencies up to around 500kHz.
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