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Copyright January 28th 1996 - Updated October 29th 2015   ..........    Brought to you by Unitech Electronics Pty. Ltd.

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NE-555 TIME CONSTANTS - Simple graphical representations

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Fig. 6 - Capacitor Charging
The capacitor charging slows down as it nears its expected charge however, in actual fact it never reaches the full +Vcc supply voltage. Please note: This is the nature of the beast, remember this. That being the case, the maximum charge it receives in the timing circuit (66.6% of the supply voltage) which is a little over the charge received after a time constant ( 63.2% ). ( Q = I x t )

Fig. 7 - capacitor discharging
The capacitor discharges slowly down until it almost discharges fully, however they never quite reach the ground potential, this is also the nature of the beast. This means there will always be a minimum voltage present in a circuit that can be measured in as it operates at greater than zero. In some cases, it is desirable to place a high value resistor across the supply rails to help "bleed-out" the capacitors. The Timing circuit is approximately 63.2% of the +Vcc supply voltage.

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Fig. 8 - Discharge Of A Capacitor
The discharge time ( t ) of a capacitor to discharge expotentially to a theoretical zero also takes time and this can be shortened by decreasing resistance (R) to the flow of current. (t= R x C )

Without a doubt, waiting for the capacitor to charge while holding a stopwatch has to be up there with watching grass grow, especially if the capacitor "C" is 1,000uF and the "R" is 1 Meg or larger. This can literally take over 1 hour for the whole thing to change state, while observing on the CRO. So, We built a special digital timer, counting upwards and incrementing and only displaying in seconds and triggering off the NE-555's "change in state" to do this mundane task. Observing this without the digital seconds counter would have been about as exciting as watching paint dry,.... seriously !!.

Basic NE-555 Operating Modes:

The NE-555 timer has two basic operational modes: one shot (monostable) and the other as astable. In the one-shot mode, the NE-555 acts like a monostable multivibrator. A monostable is said to have a single stable state and that is the "off" state. Whenever it is triggered by an input pulse, the monostable switches to its temporary state. It remains in that state for a period of time determined by an R-C network. It then returns to its stable state, awaiting a possible trigger.

So, in other words, the monostable circuit generates a single pulse of a fixed time duration each time it receives and input trigger pulse. Thus the name one-shot. One-shot multivibrators are used for turning some circuit or external component on or off for a specific length of time. It is also used to generate delays. When multiple "one-shots" are cascaded, a variety of sequential timing pulses can be generated. Those pulses will allow you to time and sequence a number of related operations.

The other basic operational mode of the NE-555 is as and astable multivibrator. An astable multivibrator is simply and oscillator.

The astable multivibrator generates a continuous stream of rectangular off-on pulses that switch between two voltage levels.

The frequency of the pulses and their duty cycle are dependent upon the R-C network values.

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Basic NE-555 One-Shot ( Monostable ) Operation:

Fig. 4 shows the basic circuit of the NE-555 connected as a monostable multivibrator. The use of the word "multivibrator" here implies it oscillates, well, it does but once only.

It should be referred to as a "toggle-ator" as it toggles from one state and stops in another state, ie: going from high to low or low to high, depending on the circuit it is being used in. An external RC network is connected between the supply voltage and ground. The junction of the resistor and capacitor is connected to the threshold input which is the input to the upper comparator.

The internal discharge transistor is also connected to the junction of the resistor and the capacitor. An input trigger pulse is applied to the trigger input, which is the input to the lower comparator.

With that circuit configuration, the control flip-flop is initially reset. Therefore, the output voltage is near zero volts. The signal from the control flip-flop causes T1 to conduct and act as a short circuit across the external capacitor. For that reason, the capacitor cannot charge. During that time, the input to the upper comparator is near zero volts causing the comparator output to keep the control flip-flop reset.

Figure 9A - MonostableFigure 9A - Monostable

Notice how the monostable continues to output its pulse to pin 3 regardless of the inputs "swing" back up. The reason for this is because the output is only triggered by the input pulse, the output actually depends on the capacitor charge CX.

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Basic NE-555 Monostable Mode:

The NE-555 in fig. 9 A is shown here in it's utmost basic mode of operation as a triggered monostable. One immediate observation is the extreme simplicity of this circuit. Only two components to make up a timer, a capacitor and a resistor. And for noise immunity maybe a capacitor on pin 5, this you will need a C.R.O for. Due to the internal latching mechanism of the NE-555, the timer will always time-out once triggered, regardless of any subsequent noise ( such as a bounce ) on the input trigger of ( pin 2 ).

This is a great asset in interfacing the NE-555 with noisy sources.    Just in case you don't know what 'bounce' is: bounce is a type of fast, short term noise caused by a switch, relay, etc. and then picked up by the input pin.

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The trigger input is initially high (about 1/3 of +V). When a negative-going trigger pulse is applied to the trigger input (see fig. 9a), the threshold on the lower comparator is exceeded.

The lower comparator, therefore, sets the flip-flop. That causes T1 to cut off, acting as an open circuit. The setting of the flip-flop also causes a positive-going output level which is the beginning of the output timing pulse.

The capacitor now begins to charge through the external resistor. As soon as the charge on the capacitor equal 2/3 of the supply voltage, the upper comparator triggers and resets the control flip-flop.

That terminates the output pulse which switches back to zero.

At this time, T1 again conducts thereby discharging the capacitor. If a negative-going pulse is applied to the reset input while the output pulse is high, it will be terminated immediately as that pulse will reset the flip-flop.

Whenever a trigger pulse is applied to the input, the NE-555 will generate its single-duration output pulse. Depending upon the values of external resistance and capacitance used, the output timing pulse may be adjusted from approximately one millisecond to as high as on hundred seconds.

For time intervals less than approximately 1-millisecond, it is recommended that standard logic one-shots designed for narrow pulses be used instead of a NE-555 timer. IC timers are normally used where long output pulses are required. In this application, the duration of the output pulse in seconds is approximately equal to:

T = 1.1 x R x C ( in seconds )

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The output pulse width is defined by the above formula and with relatively few restrictions, timing components R( t ) and C( t ) can have a wide range of values. There is actually no theoretical upper limit on T (output pulse width), only practical ones.

The lower limit is 10uS. You may consider the range of T to be 10uS to infinity, bounded only by R and C limits. Special R( t ) and C( t ) techniques allow for timing periods of days, weeks, and even months if so desired. Also cascading several NE-555 circuits will have the very same longer effect.

However, a reasonable lower limit for R( t ) is in the order of about 10 Kilo ohm, mainly from the standpoint of power economy. If one was choosing a devide the CMOS version would be ideal in that it does consume lower power, even when in standby mode.

Although R( t ) can be lower that 10K without harm, there is no need for this from the standpoint of achieving a short pulse width.) A practical minimum for C( t ) is about 95pF; below this the stray effects of capacitance become noticeable, limiting accuracy and predictability.

Since it is obvious that the product of these two minimums yields a T that is less the 10µS, there is much flexibility in the selection of R( t ) and C( t ). Usually C( t ) is selected first to minimize size (and expense); then R( t ) is chosen.

The upper limit for R( t ) is in the order of about 15 Mega ohm but should be less than this if all the accuracy of which the NE-555 is capable is to be achieved.

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The absolute upper limit of R ( t ) is determined by the threshold current plus the discharge leakage when the operating voltage is + 5 volt.

For example, with a threshold plus leakage current of 120nA, this gives a maximum value of 14 Meg Ohm for R ( t ) ( Indeed, a very optimistic value ! ).

Also, if the C( t ) leakage current is such that the sum of the threshold current and the leakage current is in excess of 120 nA the circuit will never time-out because the upper threshold voltage will not be reached.

Therefore, it is good practice to select a value for R ( t ) so that, with a voltage drop of 1/3 V+ across it, the value should be 100 times more, if practical.

So, it should be obvious that the real limit to be placed on C ( t ) is its leakage, not it's capacitance value, since larger value capacitors have higher leakages as a fact of life. Low-leakage types, like tantalum or NPO, are available and preferred for long timing periods. It is sometime wise to check the ESR first.

Sometimes input trigger source conditions can exist that will necessitate some type of signal conditioning to ensure compatibility with the triggering requirements of the NE-555.

This can be achieved by adding another capacitor, one or two resistors and a small signal diode to the input to form a pulse differentiator to shorten the input trigger pulse to a width less than 10uS ( in general, less than T ).

Their values and criterion are not critical; the main one is that the width of the resulting differentiated pulse (after C) should be less than the desired output pulse for the period of time it is below the 1/3 V+ trigger level.

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There are several different types of NE-555 timers manufactured today. The LM-555 from National was the most common one in the days of late 1996.

The Exar XR-L555 timer is a micropower version of the standard NE-555 offering a direct, pin-for-pin compatible substitute device with an advantage of a lower power operation making it ideal for battery and other portable applications etc.

It is capable of operation of a wider range of positive supply voltage from as low as an incredible 2.7 volt minimum up to 18 volts maximum, Previously 15V !. At a supply voltage of +5V, the L555 will typically dissipate of about 900 microwatts, making it ideally suitable for many diverse and innovative battery operated circuits.

The internal schematic of the L555 is very much similar to the standard NE-555 but with additional features like 'current spiking' filtering, lower output drive capability, higher nodal impedances, and better noise reduction system. A true and positive step forwards.

See at Maxim's ICM-7555, and also at Sanyo's website LC-7555 models are a low-power, general purpose CMOS design version of the standard NE-555, also with a direct pin-for-pin compatibility with the regular NE-555 as well as the ICM-7555 from NXP (Phillips) and the more recent CMOS version, the CSS-555C by Custom Silicon Solutions Inc.

CSS 555 C Data

It's main advantages are very low timing / bias currents, low power-dissipation operation and an even wider voltage supply range of as low as 2.0 volts to 18 volts.

At 5 volts the 7555 will dissipate about 400 microwatts, making it also highly suitable for battery operation. The internal schematic of the 7555 (not shown) is however totally different from the normal NE-555 version because of the different design process with cmos technology. It has much higher input impedances than the standard bipolar transistors used. The cmos version removes essentially any timing component restraints related to timer bias currents, allowing resistances as high as practical to be used.

This very versatile version should be considered where a wide range of timing is desired, as well as low power operation and low current sync'ing appears to be important in the particular design.

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A couple years after Intersil, Texas Instruments came on the market with another cmos variation called the LINCMOS (LINear CMOS) or Turbo 555.

In general, different manufacturers for the cmos 555's reduced the current from 10mA to 100A while the supply voltage minimum was reduced to about 2 volts, making it highly ideal type for 3 Volt applications.

The CMOS version is the choice for battery powered circuits, however, on the negative notes side for the CMOS 555's is the reduced output current, both for sync and source, This is not really a problem as a FET or a NPN or PNP transistor can be added as an amplifier or a heavier switching output device if so required.

For a simple comparison, the regular NE-555 can easily deliver a 200mA output versus between 5mA to 50mA for the 7555. The specifications for the CSS-555C (see below).

CSS 555 C Data

On the work test bench the regular NE-555 reached a limited output frequency of 180Khz while the 7555 easily surpassed the 1.1Mhz mark and the TLC-555 ceased at about 2.4 Mhz. Components used were 1% metal film Resistors and high quality low-leakage capacitors, supply voltage used was 10 Volt DC regulated as well as being well filtered, well "smoothed" by using by-pass caps etc.

Naturally, the results observed were remarkably different to what one would expect by using generic off-the-shelf average specification components. The results were predictable and noteworthy anyhow.

Some of the less "desirable properties" of the regular generic NE-555 are high supply current, high trigger current, double output transitions, and inability to run with very low supply voltages, an example was: 4.5 Volts DC. These problems have been remedied in a collection of CMOS successors.

A word of caution about the older regular NE-555 timer chips, such as the older NE-555, the SE-555 along with some similar brands of older timer ic's, these can generate huge ( approx 150 mA ) supply current "glitches" during each output transition. Please be aware of this factor.  

Be very sure to use a hefty bypass capacitor over the power connections near the timer chip. And even so, the NE-555 may have a tendency to generate double output transitions.

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     Basic NE - 555 ASTABLE ( MULTIVIBRATOR ) Operation:

Figure 9B - Astable ExampleAstable-MULIVIRATOR Example

Basic NE-555 Astable (multivibrator) operation:

Figure 9B shows the NE-555 connected as an astable multivibrator. Both the trigger and threshold inputs ( pins 2 and 6 ) to the two comparators are connected together and to the external capacitor.

The capacitor charges toward the supply voltage through the two resistors, R1 and R2. The discharge pin ( 7 ) connected to the internal transistor is connected to the junction of those two resistors.

When power is first applied to the circuit, the capacitor will be uncharged, therefore, both the trigger and threshold inputs will be near zero volts (see Fig. 10A).

The lower comparator sets the control " flip-flop " causing the output to switch high. That also turns off transistor T1. That allows the capacitor to begin charging through R1 and R2. As soon as the charge on the capacitor reaches 2/3 of the supply voltage, the upper comparator will trigger causing the NE-555's internal " flip-flop " to reset.

That causes the output to switch low. Transistor T 1 also conducts. The effect of T 1 conducting causes resistor R2 to be connected across the external capacitor. Resistor R2 is effectively connected to ground through internal transistor T1. The result of that is that the capacitor now begins to discharge through R2.

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 NE - 556       NE - 558       ICM - 7555  Timer chips

The only major differences between the single NE - 555, the NE - 556 ( a Dual 555 ) and a NE - 558      ( a Quad 555 ) are the power rails.

Both NE-556 and NE-558 are 14-pin chips) with different pin configurations for power and Ground.

For the other remaining pins it will require you to download from here the PDF for each device from our web site for further study before using as errors are costly and fried chips ( semi's ) do not smell too good either !

The 8-pin NE-555 Versus the ICM-7555 Note: The CMOS version ICM-7555 by NXP requires studying before using.

As you would expect, it has its own characteristics for power in, power out and over-all power consumption. The ICM-7555 in Astable or multivibrator mode will oscillate up to 500MHz as opposed to the earlier 1971-1979 NE-555's of a mere 200MHz.

It is pin-for-pin compatible, however being a CMOS device, the internal ICM-7555's circuitry differs in many ways.

Most measurements are shown as being in Pico-Amps as opposed to the NE-555 being in Milli-Amps . Therefore, we strongly urge you to please download the PDF and examine the distinct advantages of either device before using.

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Data Sheet downloads are available here on our web site

Initial charge-up

At the point where the voltage across the capacitor reaches 1/3 of the supply voltage, the lower comparator is triggered.

This event causes the control "flip-flop" to set and the resultant output to go high logic. Transistor T 1  ( Fig.3 ) cuts off and again the result is, the capacitor begins to charge.

This charging and discharging cycle continues to repeat with the capacitor alternately being recharged and discharged, as the internal two comparators cause the flip-flop to be repeatedly set and reset, depending on the frequency set by you, the designer of the circuit layout.

The net result is an output that is a continuous stream of nice clean rectangular usable "clock" pulses.

The frequency of operation of the astable circuit is dependent upon the values of R1, R2, and C. The frequency can be calculated with the following formula:

f = 1/( 0.693 x C x ( R1 + 2 x R2 )

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The Frequency f is in Hz, R1 and R2 are in ohms, and C is in farads. Typically Micro-Farads (µF) are used. The time duration between these pulses is known as the 'period' and is usually designated with as " t ". The pulse is on for t1 seconds, then off for t2 seconds.

The total period ( t ) is t 1 + t 2    ( see fig. 10 ). That time interval is related to the frequency by the familiar relationship:

f = 1/t  or  t = 1/f

The time intervals for the on and off portions of the output depend upon the values of R1 and R2.

The ratio of the time duration when the output pulse is high to the total period is known as the duty-cycle.

The duty-cycle can be calculated with the formula:

D = t1/t = ( R1 + R2 ) / ( R1 + 2R2 )

You can calculate t1 and t2 times with the formulas below:

t1 = 0.693 ( R1+R2 )C

t2 = 0.693 x R2 x C

The NE-555, when connected as shown in Fig. 9b, can produce duty-cycles in the range of approximately somewhere between 55% to 95%.

A duty-cycle of 80% means that the output pulse is on or high for 80% of the total period.

The duty-cycle can be adjusted by varying the values of R1 and R2. remembering that a 2.2K ~ 10K between supply voltage +Vcc and pin 2 just to stop a total melt down if a potentiometer is used to crank up the speed as in an relaxation oscillator or pseudo clock frequency generator.

Basic NE-555 Applications:

There are literally thousands, maybe 10's of thousands of individually unique ways that the ubiquitous NE-555 can be used in any or all electronic circuits. In almost every case, however, the basic circuit is either a one-shot or an astable. The application usually requires a specific pulse time duration, operation frequency, and duty-cycle.

Additional components may have to be connected to the NE-555 to interface the device to external circuits or devices. In the remainder of this experiment, you will build both the one-shot and astable circuits and learn about some of the different kinds of applications that can be implemented.

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Basic simple NE - 555 Free sample Circuits:

We have added-in a range of NE-555 circuit samples below for your perusal. Please experiment with them and have fun, electronics should be fun for everyone. Try ( within reason ) different component values and use the simple formulas mentioned earlier to calculate your final results. Make only small changes and observe the results and note your results, do everything in increments.

Do not exceed 200 KHz oscillation on any older NE-555 ! Tuning for maximum smoke is not good !

The most important thing to remember: Note: For correct by-the-book monostable operation with the NE-555 timer, remember the "negative-going" trigger pulse width should be kept quite short when compared to the required output pulse "width".

Values for the external timing resistor and capacitor can either be determined from the previous formulas. However, you should stay within the ranges of resistances shown earlier to avoid the use of large value electrolytic capacitors, since they can tend to be leaky. Tantalum capacitors, low E.S.R. low leakage electrolytics or mylar types and some brands of monolithic ceramics should always be used.

For +Vcc supply noise "immunity" on most timer circuits we recommend a the simple addition of a ceramic 0.01uF (10nF) capacitor between pin 5 and ground. In all circuit diagrams below we have used the LM-555CN timer IC from National Semiconductor, but the NE-555 and other brands should not give you any problems.

Now, please bare in mind, the noise on the supply line that is created by a NE-555 operating. It is always good electronic practice to place fairly large value capacitors, say to the order of 470 µF 25V or 1000 µF   25 V when using the NE-555 as we and many other NE-555 users have noted the spurious and "dirty " harmonics from most brands of NE-555 chips. The addition of a 10 µF tantalum capacitor, a 470 µF electrolytic and a ceramic 0.01µF seems to work.

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NE-555 darkness alarm  NE-555 power fail alarm  NE-555 mercury switched sample & Hold  NE-555 photo-eye-alarm  Metronome sound
practice-oscillator  NE_555_cw-prac-rcvr  NE_555_760sec-timer  NE_555_schmitt-trigger  NE_555_improved-timing
NE_555_missing-pulse  NE_555_hi-lo-siren  NE_555_tape-beeps  NE_555_decision-maker  NE_555_1Hz-oscillator
NE_555_logic-probe  NE_555_extend-timer  NE_555_HEF4017 datasheet pdf  NE_555_neon-lamp-tester  NE_555_infra-red-transmitter
NE_555_lamp flasher  NE_555_improved-oscillator  NE_555_touch-switch  NE_555_switch-debouncer  NE_555_stable-monostable
NE_555_pin-differences  NE_555_temperature-ratings  NE_555_frequency-duty-cycle-calcs  NE-xxx-data-downloads  NE_555_acknowledgements.gif
             FREE  NE - 555 CIRCUITS  to  EXPERIMENT  WITH.
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Safety First is our priority- Be aware of 240V mains
The copper plate text (above)

9 Volt Battery Eliminator:   Figure 0
Safety First is our priority - A Useful 240V mains battery eliminator

9 Volt Battery Eliminator: Figure 0 (above)

As mentioned above in the " copper plate " text above, we endeavour to keep all projects safe for all folks to use.

Well, as simple as it is in construction, we are sure some one will join the "Darwin Club" and be killed by their own stupidity. Yes, often with the greatest of plans, someone will try to re-invent the simplest of concepts and gets hurt or worse, burnt or killed. WARNING - Mains voltage kills you dead - WARNING..

There is no legislation against stupidity, however having said that, if the constructor assembles the small battery eliminator circuit carefully and uses an approved Plugpack (aka a Wall-wart ) then the risk is greatly reduced.

There is no need to open the plug pack as it is sealed for your protection and please do not try to undo what has been approved. If your plugpack / wall-wart comes with a polarised plug, please use it with the appropriate socket, rather than destroying it by cutting off the plug.

The centre pin of the 7809 voltage regulator IC is common with the metal mounting tab, both are to go to 0 volts, earth, ground, deck whatever you wish to term it as.  It uses the very basic of parts and can be purchased from us or any one else nearby. The 4 rectifier diodes are generic 1N4001, 1N4002 etc. You may choose to use a bridge rectifier component instead. That is great also. You may elelct to construct it on Vero board or perf board, a copper foiled board use as an easy way to make one-off jobs.

We suggest placing the battery eliminator in a a small UB1 Jiffy box , not only for saftey, but more for protection of the item itself. You may want to add a RED LED and small 470 Ohm resistor to let you know when it is active and running.  That is a great idea also.

As a 9 Volt AC ( rated at 1 Amp ) plugpack / wall-wart is used, once it is bridge rectified, this becomes 12.7 Volts DC ( 9.0 x 1.414 = 12.726 V ) with a 4700µF capacitor this will rise slightly.

You may wish to use what you have on hand, a minimum of 1000µF is good at 25V DC rated. The C2 10µF can be 16 Volts DC minimum rated and the ceramic 0.1µF capacitor can be rated at 50V DC.

The small 10µH ( micro Henry ) choke can be purchased from us or from any good electronics supplier.

Dark Detector

Darkness Detector: Figure 1 (above)

This is indeed an interesting circuit which has the facility to sound an alarm if it suddenly gets too dark compared to the previous light level. A simple use for this circuit would be its use to notify someone when a globe (or light bulb) fails to operate or is open circuit.

The darkness detector uses a regular cadmium-sulphide LDR (Light Dependent Resistor) to sense the "quick" absence of light falling on the LDR and to operate a small and quite cheap 8 ohm speaker. The LDR enables the alarm when light falls below a certain level. Calibration could be effective if a 47K potentiometer was added in series with the LDR.

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Power Failure Alarm

Power Failure Alarm: Figure 2 (above)

This circuit can be used as a simple yet effective audible 'Power-Failure Alarm'. In this cunning application it uses the NE-555 timer as an oscillator biased off by the presence of line-based DC voltage at Pin 7.

When the line voltage fails (monitored 9V line), the bias is removed, and the alarm tone will be heard in the piezo-electric speaker. Choose a Piezo around the 105dB mark.

R1 and C1 provide the DC bias that charges capacitor C1 to over 2/3 Vcc voltage, in this case, about 6.0 V thereby holding the timer output low. Diode D1( 1N4148 / IN914 ) provides DC bias (approx 5.4V) to the timer-supply pin 8 and optionally float-charges a rechargeable nickel metal hydride 9 volt battery across D2. R4 10 ohms is optional if needed. When the line power fails, the 9V input via D3, DC is applied to the timer through D2. resulting in a very audible sound. Experimentation with higher voltages such as 12 V DC can result in some novel and some interesting educational concepts coming to fruition.

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Mercury Tilt Switch Alarm

Fig. 3 Tilt Switch: Figure 3 (above)

This clever ICM-7555 application is basically an alarm circuit, it displays how to use a ICM-7555 timer and a simple small glass mercury switch to indicate an alarm condition, either by forced movement or by the act of tilting a protected item. Yes, it can be argued that a simpler circuit using less parts can be deployed here, however, it is an example of how to use a NE-555 IC or in this case, the ICM-7555 by NXP (Phillips).

The ICM-7555 is there to serve as a "pseudo-latch", by closing the circuit, the 470K is pulled "low", pin 2 is sent low and triggers the ICM-7555 retaining or " memorising " the last closed circuit state by the closing of the mercury switch.

Resetting is via SW-2.  Output " high " from pin 3 drives the base of Q1.  Check first your transistor "specs" for base saturation values and calculations. A 2N2222 should switch well with R3 as 1K ~ 1K8 depending of course on the load, a relay with a 350 ~ 600 ohms coil will suffice.   Don't forget to add a protection diode across the relay pointing to + ve.

As far as we know, there is no other metal which is a liquid at room temperature. Mercury (Hg) is such a metal and has some unusual and unique properties which are diametrically opposed to the properties of water surface tension and side adhesion. Water exhibits the property of a "concave" surface tension whereas mercury displays the exact opposite characteristic of having a convex surface tension. While water is widely accepted as a conductor of electricity, to make it work successfully as a "switch" it requires "ionisation", ie: adding some salt or sulphuric acid, but that is another topic that will not be canvassed here.

The mercury switch is carefully inserted into a short 20mm tube of plastic then mounted in its normally 'open' position, in which this allows the ICM-7555 timer's " trigger " pin 2 to stay high being fed via R1 470K. The ICM-7555 has lower current usage.

Pin 3 output will stay low, as established by C1 0.1µF on startup acting upon pin 4.   When the mercury switch is disturbed via vibration or movement thus causing its contacts to be bridged momentarily by the liquid mercury, the ICM-7555 latch is set to a high output level where it will stay even if the switch is returned to its starting position thus driving the base of Q1 via Rx (R3) which may be as low as 560 Ohms.

Please observe static electricity CMOS handling procedures with this CMOS device.

The high output can be used to enable an alarm of the visual or the audible type. Reset switch SW2 will silence the alarm and reset the latch. Note: Due to the required characteristics of the Vcc +ve turn on, C1 must be ceramic 0.1uF ( 100 nF ) capacitor.

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Photo-Electric Eye Alarm

Photo-Electric Eye Alarm: Figue 4 (above)

The Photo-Electric Eye Alarm is similar circuit like the Darkness Detector of Figure 1. The same type of Photo-LDR (light dependent resistor) is employed as in Figure 1. The pitch tone for the speaker can be set and adjusted with the 470K ohm potentiometer. One of the great ideas here, is to send a beam of light via a tube approximately 30 cm long with a standard 5 watt bulb (or similar) across a doorway or even a room and use this beam of light as an alarm, so, when the beam is broken, the NE-555 provides an audible indication of a "intrusion". This is similar to LED based systems currently in use today.

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Adjustable Pocket Metronome

The Adjustable Pocket Metronome: Figure 5 (above)

A Metronome is a one of the most widely used devices in the entertainment and music industry.

With a rhythmic " toc-toc " sound you can set the tempo of a piece of music to the correct beats per minute, the speed of which can be adjusted with the VR1 250 K potentiometer, providing the desired " beat " or " tempo ". R1 and R2 with C1 form the approximate 50% duty cycle.

A metronome is also a very handy tool if you new to learning to play a music instrument and need to maintain the correct rhythm as it was intended by the original lyric and rhythm composers on the sheet music or "by ear".

It can be made to fit neatly in a small "Jiffy Box" and as it is powered by a 9 Volt battery, the size can be reduced to what ever compact size you need. Remember to drill the holes before attempting to mount and adhere your small 8 ohm speaker with contact adhesive.

Using a sharp scriber, make a circular scribe around the outside of the speaker and then divide the circle into 4 equal parts then into 8 and using smaller "rings" say... 12mm from the centre, make smaller scribe circles intersecting the 8 lines.

Now, make a larger circle of , say 24mm from the centre and at each of the 8 lines drill your holes. You should now have 17 holes including the one in the centre.

Drill a series of 4mm ~ 5mm holes in a circular pattern to facilitate the "toc-toc" sound existing the small plastic jiffy-box. A volume control could be added, but only if required.We suggest a 100 ohm ~ 250 ohm potentiometer after the 10uF C2 capacitor.

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C-W Keyer

C-W Practice Oscillator: Figue 6 (above)

C-W is the abbreviation for Continuous Wave or simply Morse-Code. S.O.S. or dot-dot dash-dash dot-dot .. -- ..

You can utilise this neat circuit to practice the morse-code with this circuit, perhaps to get your amateur (ham) radio license .

Surprisingly enough, morse is the "fall-back" form of communications, that is to say, once all radio communication has gone down morse signals can still be made using the most primitive of "spark transmitters", even a car coils can be used in the hands of a person versed in morse code. Dots are a quick noise, dashes are three to four times the width of a dot in morse code.

It is very often used to communicate between submarines (visually by blinking the light from the periscopes) and is still taugh in all military schools as a back-up communication, just in case modern radios "bite the dust". Very useful communications indeed.

The VR1 150K potentiometer is for the 'pitch' and the 15K is to adjust the speaker's volume.

The "Key" SW2 is a standard morse code key, these are available in most good electronics shops.

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C-W or Continious Wave Monitor

C-W Monitor: Figure 7 (above)

This ingenious little NE-555 circuit monitors the morse code " on-air " via the "tuned circuit" connected to pin 4 and the short wire 900mm antenna.

The 100K potentiometer controls the tone and pitch.

It is open to a small amount of experimentation for the end user to achieve the best results.

We found it quite fascinating how simple and easy to use it was based on the circuit details.

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10-15min-Timer  Click this picture for more circuits

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12 Minute (760 seconds) Timer: Figure 8 (above)

This neat little circuit can be used as a quiet time-out warning for Ham Radio operators as required by The Australian Communications Commission (A.C.C.) requires that a Amateur Radio (HAM) operator identify his or her station by giving his or her call-sign at least every 10 minutes, basically operating under the same rules that govern commercial AM and FM radio stations.

This can present itself as a small challenge, especially when carrying on lengthy intense discussions as well as in depth conversations resulting in one actually loosing all track of time while "chatting" with another. A visual indication is used with no "beep", however if you wish, you can add-on a small NE-555 oscillator circuit.

The NE-555 comes to the rescue in this simple quiet circuit and is used as a one-shot so that a visual warning indicator becomes active after 10-minutes. You set it for whatever time you wish the NE-555 to take to trigger and change state. Maybe 10 mins or less, you choose, with the circuit suggested here, you can set the time from 6 seconds to 760 seconds.

It can be further cascaded to a second NE-555 that is setup as a simple "beep" oscillator as in FIGURE 6A . At the commencement of conversation, turn it on, the red LED will light-up, next remember to the reset switch which will causes the Green LED to light up. After timing out the green LED extinguishes and the RED LED turns on.

The circuit (Fig.8) shows R2 as 2K2, this circuit can operate still well without the R2 connected. Upon experimentation, it was found that virtually any value, for instance up to 250K ohms worked without effect and the timing or the operation, noting that connecting the CRO probe will trigger the NE-555. It was also revealed that by hanging a small 30cm (1ft) insulated wire off  pins 2 & 4  "in situ" and connected to pin 2, the mere "close" contact with that insulated wire triggered the NE-555 to change states. Be aware of the created "sensitivity" to induced "noise" by having the NE-555 configured in this manner. Here in the described circuit we used a 2K2 resistor as that was what was "laying around" at the time.

Operation is simple:

After 10 minutes, set by the 4M7 (4.7M) potentiometer VR1, the 'Red' LED will light to warn the operator that he or she must identify and , if the circuit in FIGURE 6A is implemented, a short "beep" from an aditional NE-555 oscillator circuit will assist in sticking to the A.C.C. rules. Using a trusty digital stop watch , adjust VR1 to indicate 10 minutes or as close to it as you can. Sitting there, waiting for the prescribed 10 minutes or even less to occur is about as boring as watching a small block of ice melt.

We can be well assured that the A.C.M.A. sits there, highly productively, wasting time just to catch you. Your taxpayer dollars at work?

Read this below and make up your own mind

The A.C.M.A rules the waves .... Oh really? .... the air-waves that is aka " the radio/TV spectrum ".

Yes Folks, the Australian Government actually believes it owns the Radio and TV spectrum !

We had absolutely no idea that they actually "own" the air-waves or spectrum. This begs the question, who did they buy them from ? We are of the firm belief that the air-waves or radio spectrum exists in nature and as such, no one entity can claim ownership of it.

It states on the A.C.M.A. website from time to time that they are auctioning-off parts of the radio spectrum. Now our simple understanding of common law is, in order to sell/auction something, you must first and foremost, 100% own the said item that you are selling/auctioning.

That is to state, you hold clear and free legal tile of the said goods. It must not be encumbered or under a caveat of repossession etc. We guess we must have missed reading the part that states that the Government is exempt and above the so-called law and therefore over-rules everyone.   Quite Interesting ! In two hundred and thirty years, the ownership of Australia has transformed dramatically.

This reeks of a certain similarity to the insane scams of people claiming they own the moon and selling off "moon real-estate", or other concepts which are just as absurd, trying to sell sunshine as a merchantable commodity, yes, maybe they will tax it? but that of course is a folly in itself, but none-the-less, the Australian Government claims ownership of our radio spectrum, how quaint!

That also begs a further question, just how far do they assert ownership of the spectrum ? Does it stop at the edge of space or what ? To date, no-one can direct us in the direction of how, when and why the Government became the said owners of a naturally occurring intangible item such as a radio spectrum.

The spectrum cannot be bottled, boxed or controlled by anyone, it existed long before Captain James Cook   ( a runt of a man ) and his bunch of invading British pirates / tourists arrived on Australia's shores, bringing with him, so-called British justice, a fair go for everyone, democratic respect of the local Indigenous population of Aboriginies, who have existed here for between 60,000 and 100, 000 years! and a recognition and respect of these traditional owners land rights,   yeah right !...   As if .... I think not ! !!

It is a pity that Cook and his crew did not learn to get along with the Australian Aboriginal population,   there was so much wealth of knowledge that could have been exchanged, however being sent here to conquer and establish a colony for British and some Irish "so-called" prisoners was high on Cook's "to do list" and any native titles were quickly squashed by the stoke of a pen and a musket bullet, so ... the bullying started right then, so " might is right " and do not try to change it and sadly it continues very much today.

In the Sandwich Islands or Hawaii as we know it today, the local people sorted this " little runt " out, Captain James Cook died by being speared to death.   Obviously the inhabitants of the Sandwich Islands knew how to deal with these sort of invading people.

So, does the Government have some monopoly over all the area of Australia extending from terrestrial earth to a distance out in space ? Does this come under " THE RIGHT BY CONQUEST, or CONQUERING THE INDIGENOUS AUSTRALIAN ABORIGINIES " by an illegal invasion ?

Curious questions ? Under section 52 of the Trade Practices Act, selling/offering for sale when you do not have 100% ownership is fraud. Upon reading these "so-called" laws, there are several that apply in simple recognition of the truth, you cannot sell something, nor auction something nor for that matter attempt to trade, hire, sell, auction anything that you do not legally own. It is against the rules.  Full stop.

This monopoly was set up almost two centuries ago with absolutely no consultation with the traditional owners of the lands that Cook and his invading red coats and as well as those who followed him, all set up an illegal regime in the name of one King George 3rd ( who was officiall removed for being a nutter).

Having asked the question : Who did they buy it from and when and how much was paid, these questions were all rejected and we were directed to a Government A.C.M.A. website and given directions to read a certain PDF.  This said PDF did in no manner state or contain these words eg: " ownership ", " payment " or the limits and sizes of the claimed ownership of this radio spectrum. Is this fraudulent ?? We think so.

For more information about the Government's A.C.M.A. web site click on C-tick info gadget (below)

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