EdITS WORLD Uncategorized The Monostable 555 Timer

The Monostable 555 Timer

555 hours per hour

The operation and output of the mono-stabilizer 555 is exactly the same as the transistor described in the Multi-Traceability Uniform tutorial. The difference is that the 555 timer is replaced. Consider 555 hours of circuits below.

555 tangible time

When a negative pulse (0 V) is applied to the mandatory input (pin 2) of the configured oscillator 555, this input is detected in the internal comparator (comparator # 1) and “sets” the state of the chipboard through switching the output off from “LOW” to “HIGH” mode, this process removes the connection transformer connected to pin 7, removing the short circuit from the external C1 capacitor connection.

This allows the simultaneous capacitor to be cut by a R1 resistor up to the voltage across the threshold voltage capacitor (pin 6) reaching 2/3 Vcc set by the internal voltage separation of the network. At this time, the comparator outputs up and the flip-flip is reset to the original position, the transistor turns and drops, and the capacitor releases the ground with a pin 7. Then the output changes status. Return to the stable “LOW” key and wait until the timer has a new trigger pulse. So, as before, many chibears have no solid position.

The 555 tactile timer circuit is applied with a negative pulse applied to pin 2 and this stimulus pulse should be shorter than the output pulse width and therefore the time synchronizer capacitor. completely discharged and then time. After the development, monostable 555 will remain “HIGH” in an unstable state until the end of the time specified by the R1 x C1 network. The time in which the output voltage remains “HIGH” or logic level “1” is given through the following constant time comparison.

Where in seconds, R Ω and C are Farad.

555 samples of timer # 1

A 555 timer is required to generate a timer in a circuit. If a 10 μF synchronization capacitor is used, calculate the resistor value required to produce a minimum output delay of 500 ms.

Answer 500 ms for 0.5 seconds. Changes in the previous formula we find the calculated value for R resistance as follows:

The value of the synchronization resistor is required to produce the required time constant of 500 ms, so 45.5 kΩ. However, since the resistance value of 45.5 kΩ is not present as a default value resistance, the nearest available resistance value of 47kΩ must be selected in each common concession area. E12 (10%) up to E96. (1%), which gives a new delay calculation of 517 ms.

If this difference of 17 ms (500-517 ms) is not acceptable other than a single resistor, two resistors of different values ​​can be linked to the set to fix the duration of the pulse to a desired value, another value chosen for the synchronization capacitor.

We now know that the delay or length of the output pulse at a 555 mono timer is determined by the timeframe of the Rc connected network. If a long delay of 10 seconds is required, it is not always recommended to use high quality synchronization capacitors as it can be physically, expensive and good, for example ± 20%. ,

Another approach is to use a low capacity synchronous capacitor and higher resistance of up to 20 MΩ to generate the required delay. By using different capacitor timer values ​​using different switches attached by multi-rotary switches, we can create a 555 clock opener circuit that can produce a different pulse width per revolution. Change, like. B. the tangible 555 timer shown below.

A 555 convertible timer

We can calculate the R and C values ​​for the individual components required, as in the example above. Selecting the components needed to get the desired delay, allowing us to place kilohms (om), megohms (milligrams) on microfrades (UF) or calculate in Picafarad (pf), and is easy enough a delay is a factor of ten or even a hundred.

We can make life a little, using a type of graph called “nomograp” through which we can find the expected frequency of one-shot output for different combinations or values ​​of R and C. For example

Printable nomenclature

By selecting the appropriate values ​​for C and R in the range 0.001 uF to 100 uF and 1 kΩ to 10 M, we can see the expected output frequency directly from the nomogram, thus eliminating errors in calculations. In practice, the synchronization resistance value for a one-shot timer is not less than 1 kΩ and not more than 20 milligrams.

Tangible timer 555

In addition to the tangible configuration of 555, we can make an impossible device (two solid states), the operation and output of Bistable 555 such as the transistor previously described in the Multiple Tutors of Teaching.

555 Stainlessly one of the simplest circuits we can build on the 555 timer chip: in this configuration, no synchronized Rc network is used to generate output waveform, so it is necessary to calculate the length of the circuit. . Consider the observable timing circuit 555 below.

Timer 555 (corrugated) impossible

The transfer of the output waveform is obtained by controlling the 555 timer and reformed inputs stored in the “HIGH” position of both running R1 and R2. Set the switch to “LOW” by pressing the trigger input (PIN 2), change the output state to “HIGH” and set an input reset (PIN 4) to “LOW”, Go to reset location, set output to “LOW” status.

The 555 timing circuit is insecure in one state or in another state and so it is immovable. So the 555 stable bistable timer is in “HIGH” and “LOW” situation. The portal input (pin 6) is connected to the ground to ensure that the reversible circuit cannot be restored as in the normal synchronization function.

Exit 555

We can not complete this 555 Timer Tutorial without discussing functions and exercises in dual-CI functionality 555 or 556.

Output (pin 3) allows for the 555 normal time or 556 timer of sufficient current for 200 mA to control the output directly such as relays, white lamp lamps, LED motors, loudspeakers, etc., resistors. in a series or protective diodes.

This capacity of the 555 timer to handle the “sink” and “source” stream means that the output device can be connected between the 555 output port and the power supply to draw energy. Commission or between departure. Clamp and ground to current charging. Example

Lowering and determining timer output 555

In the first circuit above, the LED is connected between the positive rail supply (+ Vcc) and the output pin 3. This means that the current from the output terminal of the timer 555 “absorbs” or absorbs the LED is lit. “ON” if the output is “LOW”.

The second circuit above shows that the LED is connected between output 3 and ground (0V). This means the current “source” (current) or leaves the output of the timer 555 and that the LED is “on” when the output is “high”.

The ability of the timer 555 to understand and produce its current output load means that both LEDs can be connected to the output terminal at once, but only one is active, depending on whether the state output is “HIGH”. or “LOW” The left circuit shows an example, the two LEDs are switched off and off depending on the output resistance. On R, the current LED is limited to less than 20 mA.

As we said previously, the maximum output current that the current load absorbs or composes by pin 3 to the maximum supply voltage is approximately 200 mA, and the cost is more than enough to drive or switch to another more integrated circuits. Logic, LEDs or small lamps, etc. But what if we want to switch or control higher power devices such as motors, solenoid valves, relays or speakers? Next, a transistor must be used to increase the output of 555 timers to provide enough power to control the load.

555 timer transistor driver

In the two examples above, the transistor can be replaced by a powerful MOSFET or Darlington transistor when the current load is high. When using an induction load, such as a motor, relay or electromagnet, it is recommended to connect a rotating diode (or wheel wheel) directly to the loading terminals to absorb the reverse voltages emitted by the induction device. implemented state changes.

To date, we have considered using the Timer 555 to generate single-credible and convertible output pulses. In the following tutorial on generating waveforms, we will see how to connect the 555 to an independent multi-verifier configuration. When used in a stable manner, the frequency and duty cycle of the output waveform can be precisely controlled to produce a very versatile waveform generator.

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