How IC 555 timer works? Fundamentals of IC 555 timer & its basic applications VSagar • December 16, 2011 This article was first written on 16 Dec. 2011 and now it is rewritten in simple language with more practical approach, due to huge demand from visitors. Pin-wise functioning of IC555 timer

Pin-1, GROUND: It is the GROUND PIN of the IC. The negative terminal of DC power supply or battery is connected to this pin. Here note that IC555 works always on single rail power supply and NEVER on dual power supply, unlike operational amplifiers.

Also note that this pin should be connected directly to ground and NOT through any resistor or capacitor. If done so, the IC will not function properly and may heat up and get damaged. This happens because all the semiconductor blocks inside the IC will be raised by certain amount of stray voltage and will damage the IC. Refer the block diagram of the IC for more details. For more details read elaborate collection of FAQ on this IC.

Pin-2, TRIGGER It is known as TRIGGER PIN. As the name suggests in triggers i.e. starts the timing cycle of the IC. It is connected to the inverting input terminal of trigger comparator inside the IC. As this pin is connected to inverting input terminal, it accepts negative voltage pulse to trigger the timing cycle. So it triggers when the voltage at this pin LESS THAN 1/3 of the supply voltage (Vcc).

In number of applications, the IC must be triggered by a pulse. The amplitude and minimum pulse width required for triggering depend on operating temperature and supply voltage of the IC. Generally the current required for triggering is about 0.5uA for a period of 0.1uS. The triggering voltage may be in a range from minimum 1.67V when Vcc=5V to maximum 5V when Vcc=15V. The triggering circuit inside the IC is very sensitive and may be accidently activated due to surrounding noise. To avoid this, the pin is always connected to a pull-up resistor (10k-ohm), if this pin is used separately.

Pin-3, OUTPUT This is the OUTPUT PIN of the IC. It can SINK or SOURCE a maximum current of 200mA.

Sinking the current means, when the output of the IC is at logic-0 state i.e. LOW and so it can absorb current into its output. Similarly sourcing the current means, when the output of the IC is at logic-1 i.e. HIGH and so it can give out current from its output. Due to this property of the IC, we can use it in number of typical digital applications also.

Also note that the output voltage of the IC is slightly greater than zero, when it is in logic-0 state. Similarly it is slightly less than supply voltage (Vcc), when output of the IC is in logic-1 state.[/tab]

Pin-4, RESET It is the RESET PIN of the IC. When it is connected to positive terminal of battery, the IC works normally. However, when it is grounded (either directly or through a maximum of 100k-ohm resistor), the IC stops its working completely and its timing cycle stops i.e. the charging or discharging of the external capacitor stops, so output of the IC is locked in logic-0 state.

It is interesting to note that the reset voltage required by this pin is typically 0.7V at a reset current of 0.1mA. However in general applications, this pin is always connected to positive terminal so that the IC works normally.

Pin-5, C. VOLTAGE This is known as the CONTROL VOLTAGE pin. The 2/3 of supply voltage point on the terminal voltage divider is brought out to pin-5, known as the control terminal of the IC.

The timing cycle can be modified by applying external DC control voltage to this pin. This allows manual or electronic remote controlling of the time interval of the IC.

The control terminal is frequently used when the timer is operated in MMV mode. But if you are NOT using this pin for any such purpose, then this pin MUST BE GROUNDED THROUGH A CAPACITOR OF 0.01uF. This prevents the time interval from being affected by picking up of stray AC or RF noise from the surrounding.

Also note that, when the IC is used as an oscillator, in AMV mode, we can modulate the output waveform of the IC by applying a variable DC control voltage to this pin, as shown below.

Pin-6, THRESHOLD This is known as the THRESHOLD PIN. It finalizes the timing cycle of the IC, when its voltage is equal to or greater than 2/3Vcc, the output is at logic-0 state.

Since this pin is connected to non-inverting terminal of threshold comparator inside the IC, it accepts positive going pulse to end up the timing cycle, also.

Note that the typical value of threshold current is 0.1mA, just like the RESET PIN. The time width of this pulse should be greater than or equal to 0.1uS. Refer the block diagram of the IC for more details. For more details read elaborate collection of FAQ on this IC.

Pin-7, DISCHARGE It is known as DISCHARGE PIN. It discharges the external capacitor into itself, but when fully charged…!

It is connected to the collector of an NPN transistor inside the IC. Due to this, the discharging current going into this pin MUST NOT EXCEED 50mA, otherwise the internal transistor may get damaged.

It is interesting to note that this pin can also be used as output pin with open collector output. I am working on one such practical circuit and will publish the circuit very soon.

Pin-8, +Vcc It is known as the +ve supply terminal of the IC. The battery voltage connected across this pin and ground pin SHOULD NOT EXCEED 18V. Generally the range of operating voltage of the IC is 3V–18V. Details of working

Basically, 555 timer is a highly stable circuit capable of functioning as an accurate time-delay generator and as a free running multivibrator. When used as an oscillator the frequency and duty cycle are accurately controlled by only two external components, a resistor (R) and a capacitor (C).

The circuit may be triggered and reset on falling wave forms. Its prominent features are summarized below:

Timing from micro seconds through hours Monostable and Astable operation Adjustable duty cycle Ability to operate from a wide range of supply voltages Output compatible with CMOS, DTL and TTL (when used with appropriate supply voltage) High current output that can sink or source 200 mA Trigger and reset inputs are logic compatible Output can be operated normal ON and OFF High temperature stability

Let us see the internal details and operation of IC555 and see how the various features can be developed into practical circuits.

The SE and NE versions are similar except for maximum temperature ratings. The precision type SE maintains essential characteristics over a temperature range of -55°C to +125°C while the general purpose type NE operates reliably only over a range of 0°C to 70°C. Some manufactures use the suffix C to indicate the commercial version for general purpose applications. Both types have a maximum rating of 18 volts and can handle power dissipation of up to 600 mW.

A functional block diagram of 555 timer is given below.

The device consists of two comparators two transistors, a flip-flop and buffered outputs stage. The reference voltages for the two comparators inside the 555 are produced across a voltage divider consisting of three equal resistors of 5K ohms each.

Look at the block diagram of the IC, to see that there are three resistors of 5kohm each

(highlighted with yellow pen) connected in series. These three resistors produce 1/3 and 2/3 voltage levels for controlling the action of trigger and threshold comparators inside the IC. Due to this arrangement of the three resistors, the IC has a typical code number as IC555.

The threshold comparator is referenced at 2/3 Vcc and the trigger comparator is referenced at 1/3Vcc. The two comparators control the flip-flop which, in turn, controls the state of the output i.e. either ON or OFF states.

When the timer is in the quiescent state, the internal transistor T1 is conducting and represents a short circuit across timing capacitor C. The level of the output terminals in this state is low.

In practical circuits voltage at pin-2 is kept above the trigger point by a resistor connected to Vcc. When a negative going trigger pulse on pin-2 is applied, it causes the potential at this point to fall below 1/3Vcc and thus the trigger comparator RESETs the flip-flop.

Now transistor T1 is cut-off and the thus the output level of the IC goes HIGH to a value slightly less than Vcc. Capacitor (C) now starts to charge and the voltage across it rises exponentially until it reaches 2/3Vcc. At this point, the threshold comparator resets the flip-flop and the output returns to its low state-just slightly above ground. Transistor if T1 is turned ON, discharging capacitor C so that it is ready for the next timing period.

Once triggered, the circuit cannot respond to additional triggering until the timed interval has elapsed.

The delay period, the time that the output is high, in seconds is given by – 1.1 x C x R

Where R is in Mega ohm and C is in microfarads.

Following diagram shows how delays from 10 microseconds to 10 seconds can be obtained by selecting appropriate values of CT and RT in the 0.001pF to 100 pF and 1K to 10 Mega ohm

ranges. In practice, RT should not exceed 20 Mega ohm. If you use an electrolytic capacitor for CT, select a unit for low leakage. The time delay may have to be adjusted by varying PT to compensate for the wide tolerance of electrolytic.

An important feature to be noted here is that 555, unlike many RC timers, provide a timed interval that is virtually independent of supply voltage Vcc. This is because the charge rate of C and the reference voltages to the threshold comparator and trigger comparator are all directly proportional to the supply Voltage. Operating voltage can range from 3V to 18V. Important formulas for calculations

Frequency Calculations To calculate the output frequency of the circuit following formula is used. In this you have to put the values of R1, R2 and the value of timing capacitor C. Note that R1 and R2 are in Ohms and C is in Farad.

image51

This sounds good so far as theoretical calculations are concerned. But when you deal with practical circuits and want to use this formula, then what to do? The formula contains three unknowns…! So how to calculate the output frequency?

I have discussed this issue in one of the following comments. You may read the comments, given below, to resolve the problem of your practical calculations.

Timing Calculations The total time period, the On time and Off time period of the IC are given by the same formula.

The timing calculations will give you time in seconds, if the values of R1 and R2 are in Ohms and the value of timing capacitor is in Farad. Read the practical application of calculating your timing values.[/tab]

Duty Cycle The duty cycle of the IC is actually a specific ratio of the two resistors used in AMV

circuit. Thus the formula for duty cycle of the IC is given by the same formula. The duty cycle of the circuit is always calculated in terms of percentage. There are three main values of duty cycle of the IC.

When duty cycle = 50%, we get the perfect square wave at the output of the circuit. When duty cycle > 50%, we get a rectangular wave, such that ON TIME of the circuit is greater than the OFF TIME. When duty cycle < 50%, we get a rectangular wave, such that OFF TIME of the circuit is greater than the ON TIME. Always remember that the value of duty cycle CANNOT BE equal to 100% and also it CANNOT BE equal to 0%. This is because, the value of R1 cannot be zero in the circuit of AMV.

More about IC555

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flipflop element. Derivatives provide up to four timing circuits in one package. Introduced in 1971 by Signetics, the 555 is still in widespread use, thanks to its ease of use, low price and good stability, and is now made by many companies in the original bipolar and also in low-power CMOS types. As of 2003, it was estimated that 1 billion units are manufactured every year.

The IC was designed in 1971 by Hans R. Camenzind (know more about him on Wikipedia) under contract to Signetics, which was later acquired by Philips. Depending on the manufacturer, the standard 555 package includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants available include the 556 (a 14-pin DIP combining two 555s on one chip), and the 558 (a 16-pin DIP combining four slightly modified 555s with DIS & THR connected internally, and TR is falling edge sensitive instead of level sensitive).

The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number designated the military temperature range, −55 °C to +125 °C. These were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) packages.

Thus the full part numbers were NE555V, NE555T, SE555V, and SE555T. It has been hypothesized that the 555 got its name from the three 5kΩ resistors used within, but Hans Camenzind has stated that the number was arbitrary.

Low-power versions of the 555 are also available, such as the 7555 and CMOS TLC555. The 7555 is designed to cause less supply glitching than the classic 555 and the manufacturer claims that it usually does not require a "control" capacitor and in many cases does not require a decoupling capacitor on the power supply. Such a practice should nevertheless be avoided, because noise produced by the timer or variation in power supply voltage might interfere with other parts of a circuit or influence its threshold voltages

Vidyasagar Sir says: December 16, 2011 at 4:07 p

The applications of IC555, will be published very soon. Srushti Patil says: December 29, 2011 at 4:07 p

Why ic 555 is called as IC555? Saurabh says: December 29, 2011 at 4:07 p

What a question? Look at the block diagram of the IC, to see that there are three resistors of 5kohm each (highlighted with yellow pen) connected in series. These three resistors produce 1/3 and 2/3 voltage levels for controlling the action of trigger and threshold comparators inside the IC. Due to this arrangement of the three resistors, the IC has a typical code number as IC555. Prasad says:

August 7, 2012 at 4:07 p

Can u please tell me why in a mono stable multivibrator(using IC 555) a capacitor is connected to the 5th pin i.e Control Voltage pin before grounding it & what is its function…? I need the answer before 9th august 2012, please.. Thank you Prasad Karnataka Prasad says: August 7, 2012 at 4:07 p

Can u please tell me why in a mono stable multivibrator(using IC 555) a capacitor is connected to the 5th pin i.e Control Voltage pin before grounding it & what is its function…? I need the answer before 9th august 2012, please.. Thank you Prasad Karnataka V!$agar says: August 8, 2012 at 4:07 p

If you observe the block diagram of IC555, you will see that pin-5 is connected to the inverting terminal of threshold comparator. If this pin is suspended as open, i.e. connected nowhere, then it may absorb external noise. Due to this, the 2/3 voltage level at this point, (see the block diagram carefully), will disturb. This will result in either increase or decrease in the timing cycle of the circuit. If 2/3 voltage level is increased, the capacitor will take longer time to charge and shorter time to discharge. So in order to avoid this problem, it is a good practice to use a 0.01uF capacitor between pin-5 and ground. This value of capacitor is so chosen, that it absorbs a broad spectrum of RF noise

and protects the circuit. V!$agar says: August 8, 2012 at 4:07 p

To clear your doubts about IC555, please also read this article of FAQ on IC555. naresh kumar says: September 13, 2012 at 4:07 p

hello sir……will u please tell mee…….how can we know that voltage falls to 1/3rdvcc…….to start timing cycle…… Vidyasagar Sir says: September 13, 2012 at 4:07 p

If you look at this circuit…

you will see that when capacitor voltage is 1/3 of Vcc, then it is sensed by the (-) inverting terminal of trigger comp. So simply its output becomes HIGH. This RESETs the RSFF and its output at Qbar = 1. In this way the timing cycle is started. To understand this, you will have to consider the IC555 as AMV only. umar says: September 20, 2012 at 4:07 p

sir,in IC555 design what is the need of transistor after flip flop. Vidyasagar Sir says: September 20, 2012 at 4:07 p

The transistor after the flip-flop is used for discharging the capacitor used in timing cycle. This transistor is necessary when we use the IC either as Astable multivibrator or Monostable multivibrator, since its collector is connected to pin-7 (Discharge pin) of the IC. vinay says: October 7, 2012 at 4:07 p

Dear Sir, I have made a simple light sensitive trigger using an IC 555 with a single relay. It works fine, but when I replaced it and placed a double relay in it, the relay does not function properly. Please help.

Regards

Vinay Vidyasagar Sir says: October 7, 2012 at 4:07 p

It is never recommended to use two relays in the output circuit of IC555. It will produce a large amount of back e.m.f. when they both switch off and will lock the output of the IC.

It is therefore recommended to use a single relay with DPDT change over. vikash kumar says: October 12, 2012 at 4:07 p

what is timing cycle? and how we can calculate timing cycle?please reply soon…. Vidyasagar Sir says:

October 12, 2012 at 4:07 p

Are you asking this question in terms of IC555? If so, then it can be explained as follows-

The timing cycle is the total time taken by the IC, to change its output from logic-1 to logic-0 state and back to logic-1 state. Thus we can say that the span of one positive half and consecutive negative half cycle are known as timing cycle.

It can be calculated very easily. If you take the reciprocal of frequency of the wave, you get its value. sostheness mallya says: October 16, 2012 at 4:07 p

please sir i need to understand well how to control the output frequency .it can be used to produce the frequency of 2-10 cycle per second.also did you no any thing about the IC 741 used as the transmitter Vidyasagar Sir says: October 16, 2012 at 4:07 p

See the equations given in the article Vidyasagar Sir says: October 16, 2012 at 4:07 p

And also see the values of Resistors Rahul says: October 19, 2012 at 4:07 p

Thanks for the great guide, it’s easy and informative to read.

I need to use a NE555 IC to create a square wave AC frequency of around 147-149 khz. What values forr R1, R2, and C do you suggest I use to create such frequencies in astable mode? Vidyasagar Sir says: October 19, 2012 at 4:07 p

Refer the article on AMV and from its formula calculate the required values. http://vsagar.com/2012/10/19/astable-multivibrator-ic555-fundamentals-amv/ Rahul says: October 20, 2012 at 4:07 p

Thanks. I had tried using some online calcs, but I wasn’t too sure about which values of R1, R2, and C would be optimal for maximising efficiency and reducing losses.

I got values of R1 = 1 ohm, R2 = 1 ohm, and C = 3.25 uF for generating my frequency. Do these values seem appropriate? Also, is it okay to connect two capacitors in parallel to obtain the required capacitance?

Thanks! Vidyasagar Sir says: October 20, 2012 at 4:07 p

For designing your own astable multivibrator circuit, always consider following points to select and calculate the values of components. This will ALWAYS GIVE YOU OPTIMUM RESULTS… For particular timing say ‘x’ (such that ‘x’ is less than or equal to 5 min), select R1=1kohm first. Using this value of R1, protects the discharge transistor inside the IC. Now if value of ‘x’ is in several minutes, then select C = 100uF or more.

If the value of ‘x’ is less than one minute, then select C < 100uF. Now calculate the value of R2, using the formula, as given above. If the value of R2 comes to be rather odd value (i.e. it is not a standard value), then take a nearer possible standard value or use a variable resistor, instead. ALWAYS REMEMBER THAT SELECTING HIGHER VALUES OF ‘C’ MORE THAN 220uF, PRODUCES LEAKAGE IN THE CAPACITOR, AND GIVES LESS ACCURACY IN REPETITIVE TIMING CYCLES. Rahul says: October 20, 2012 at 4:07 p

Thanks again for the reply. I did try using R1=1kohm, but that made it difficult to find the right capacitors and R2 to get my desired frequency of 147-149khz. I suppose that makes my value of ‘x’ very, very small! Vidyasagar Sir says: October 20, 2012 at 4:07 p

Take R1=1kohms, R2=4.4kohms (which is odd value) with C=0.001uF. This will give you 146.939KHz i.e. roughly 147KHz

Now reduce the value of R2=4.3kohms to get the frequency F=150KHz.

Now the range of R2 is from 4.4 to 4.3 only which is just 100ohms.

This range is not so easy to achieve.

So do one thing. In place of R2, in the circuit, connect one resistor (particularly high accuracy metal film resistor of 4kohms) in series with a variable WW resistor or even any LIN type, of 500ohms. Now just rotate the variable resistor to get the change in frequency from 147kHz to 149KHz, as required.

I am also interested to know the reason for using this circuit. Once you test it successfully, please do not forget to tell me the results. If possible, also send the details with photos, I will definitely publish them on this site, with your name as contributor to this site. Rahul says: October 20, 2012 at 4:07 p

Thank you so much sir! I was doubtful of the right values of our components to get our circuit working optimally, but you cleared that up for us :)

Our circuit is for constructing a prototype for conducting electricity wirelessly using resonance. We’re still in our research stage, but I feel that we only need the materials now to put our circuit into construction mode now. The 555 timer IC comes into play and that transmitter end of our circuit, which consists of large coils of copper.

Certainly, when I get my prototype working, I will give you the pics and results :) Vidyasagar Sir says: October 20, 2012 at 4:07 p

So far as the introductory part of your project, I presume that you are going to transmit high frequency signals from 147 to 149KHz through coils? Now if it is correct, then you must rethink on this idea. IF you are using IC555, then it will generate square wave. Now if you connect square wave as AC voltage to your large coils, then they will be magnetically get saturated. This is because, the square wave contains steady-state DC voltage level, after and before when its edges (either positive or negative) are completed. So if this is the way, you are going to handle the research work, it should be a total fallacy… I hope that it is not the case…. Rahul says:

October 20, 2012 at 4:07 p

Actually, although a sine wave would be better, people have been able to do simple DIY wireless electricity circuits using square waves from small function generators. In our case, we’re using IC555 to do the same thing. It’s much cheaper, and far more educational than using a function generator.

http://www.instructables.com/id/Wireless-Power-Transmission-Over-Short-Distances-U/? ALLSTEPS

Also, since our frequency is so high, saturation shouldn’t be too much of a problem. revanth kumar says: October 27, 2012 at 4:07 p

what is the definition for frequency of a square wave?since,it is a wave what is it’s wave length? Vivek Kolandairaj says: October 29, 2012 at 4:07 p

A square wave is ON(High voltage) for a period of time and OFF(Low voltage) for another period of time. Sum of the on time and off time of the square wave is called the period of the square wave. The inverse of the period is called the Frequency.

A single square wave consists of a mark(high voltage) and a space(low voltage). This mark and space together constitute one cycle. Frequency quantifies how many cycles are there in one second.

For example: a 500 Hz square wave means it has 500 cycles in one second. i.e. 500 marks and 500 spaces every second.

a 30KHz square wave means it has 30,000 cycles in one second.

In general you can define wavelength for physical phenomena that exhibit a space rate of change. i.e. pressure varying with respect to distance or Field strength varying with respect to distance. Wavelength itself means length of the wave. Length being a measure of distance.

But for electrical voltages or currents that are described in the time domain i.e. time rate of change of voltage or current, the parameter wavelength is non existent or undefined. Vidyasagar Sir says: October 29, 2012 at 4:07 p

Your discussion is very appealing. But you are trying to relate “space-time continuum” of Einstein’s theory of GTR or STR, together with electrical signals. The physical quantities (pressure, sound, etc.) that you describe have physical sense of spacerate of change. The progression of these quantities over space-time continuum, obey the laws such that their amplitude, frequency and phase are dependent. But in electrical signals, this is not the case. Their amplitude, frequency and phase are independent, as was described by Guglielmo Marconi. On this very concept, he invented radio. Juan Cruz says: November 8, 2012 at 4:07 p

Sir; I am just a new learner in electronics. My question I would like to know is… Is it possible to supply a 24 volts dc to pin number 8 where the vcc input voltage of the LM555. I will appreciate your kind response, thanks! Vidyasagar Sir says: November 8, 2012 at 4:07 p

No.

For any type of IC within the family of IC555, like LM555 or SE555, NE555, etc. the typical voltage rating SHOULD NOT EXCEED 18v maximum (minimum being 3V). So it is altogether impossible to use such higher voltage as 24V. Never allowed. The IC will simply burn out from inside and will be damaged completely. But may I ask in return, that what is the exact reason that you come across such need? Vivek Kolandairaj says: November 8, 2012 at 4:07 p

Refer the IC 555 data sheet. It lists the absolute maximum ratings for the product. If maximum ratings are exceeded, you’ll have a nice fire works show for Diwali ;) Vidyasagar Sir says: November 8, 2012 at 4:07 p

Celebrate Diwali in a different way…!!! Rahul says: November 13, 2012 at 4:07 p

I am testing my IC-555, and strangely, the output frequency is completely different when I use a 9V battery and when I use 2 9V batteries connected in series. I’m using R1=1kohm, R2=4.37kohms and C=1nF (.001uF). Frequency at 18V is much greater than at 9V I thought the output frequency from pin 3 is irrespective of the voltage, so I would appreciate it if someone could clear this up for me. Moreover, at which input voltage does the formula F=1.45/ ((R1+2*R2)*C) hold good? Vidyasagar Sir says: November 13, 2012 at 4:07 p

If the freq. is changing due to change in voltage, it means that the ic is not at all of good quality. It simply indicates that the input resistance of both comparators inside the ic is very less, and

so they are responsible to disturb the timing length, so the freq. because the charging and discharging of capacitor is being loaded.

This could only be the reason because for a true IC555 this case you are telling is impossible. Rahul says: November 13, 2012 at 4:07 p

Thanks, though the change in frequency is absolutely visible to the eye using an LED for the output. I’m using a Texas Instruments IC-555, so it’s surprising to here that the quality of the IC is poor!

Also, for our wireless electricity project, the IC fits the bill exactly; all that we need is a MOSFET to give us a square wave AC signal to pass through our coils. Our IC assembly and frequency tuning is done. Vidyasagar Sir says: November 14, 2012 at 4:07 p

Is the output of the IC being loaded?

Use a MOSFET at the output section. Preferably use P-Channel. OR use Darlington pair at the output. Rahul says: November 14, 2012 at 4:07 p

Yes, the MOSFET will go at the output; it will be in series with the coils. The MOSFET we plan to use is N-channel type, I’m not too sure whether P-channel will do exactly the same thing. Vidyasagar Sir says: November 14, 2012 at 4:07 p

Ok.

Now what else?

I am not sure, whether the circuit will work?

So far as I can recall, I had suggested you already not to use square waves for this experiment. I think, you are doing the experimental research on cordless power transfer? Rahul says: November 14, 2012 at 4:07 p

Yes sir, we are doing it on wireless power transformer, similar to how an air-core transformer works. A square wave is optimal for our project actually (albeit, it needs to be AC, not DC). The reason for square wave is that we can get a large change in flux as the wave changes from -I to I, in a very short time period. Magnetic saturation is not a problem here. The MOSFET will give us the AC we require from our DC output from the 555.

I just want to confirm whether an N-channel MOSFET works the same as a P-channel MOSFET and which one would be better for our project. Vidyasagar Sir says: November 14, 2012 at 4:07 p

If you are connecting the load to +ve rail, i.e. in drain circuit, then N-channel will be better.

If it is opposite then P-channel will do.

But using N-channel is better for 555 timer, as its output voltage will drive the MOSFET

correctly, and so the load will be driven properly. Rahul says: November 14, 2012 at 4:07 p

Excellent, thank you for your help. The MOSFETs which I ordered will come by then end of this week; I’ll surely send my results as I finish my project. Sindre says: November 15, 2012 at 4:07 p

Hello.

I looking to build a 457 khz transmitter using the IC 555 as a base. I need it to have a pulse width of 700 to 1300 milliseconds and a pulse width of 200-400 milliseconds.

Is this possible, having probem calculating this. Vidyasagar Sir says: November 15, 2012 at 4:07 p

If you are expecting the said output results using IC555, then it is perhaps not possible. Because the internal propagation delays, as per the data sheets, indicate that the required values are less in time width, as compared to the propagation delays of the IC.

I will rather suggest you to go for IC LM7555 the CMOS version of 555 timer. Seek for its output performance and then work on the calculations. Don’t waste your time in just calculations. First compare the required values with the optimum values, a particular IC can provide, and then work on it. Rahul says: November 18, 2012 at 4:07 p

The IC was just what I needed for my 10th grade science project. My wireless electricity project is working exactly as it should. Thanks for your help!

How can I submit my pictures/video material of my project in action to you, sir?

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