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This is a very basic example but does in fact work. Try some small experimentation with the values of R and C. Be aware that ohms is not the preferred value for R1 , it was placed there for a small incoming signal from a remote control over several hundreds of meters away and the filtering required for that length of cable has deliberately been left out for simplicity's sake. The correct value if driven from another source would be determined by the amount of current and voltage applied to almost saturate the base of Q1 BC thus turning it "on" so in theory, R1 presently represented as ohms could be 1K or 2K2 or higher it is of your own choice.

Briefly, if there is a missing "pulse" to the base input of Q1 BC or no signal at all, it sees it as a missing pulse inverts the signal within the NE and sounds a piezo DC buzzer. The second NE IC-2 forms a very simple oscillator, you can add this great effect for your children's toys. IC-2 forms as a multivibrator, delivering a set of tones provided by the voltages present at pin 7 of IC-2 and the interaction of R4 K and R5 12K and C2 0. Notes : It is believed that 15uF caps used at the time when the circuit was devised, are no longer made, so it is safe to use 22uF caps.

Recording Beep: FIGURE 12 above As you may be aware, it is actually highly illegal in this country to record any phone conversation without the "other party's" full permission.

This circuit is used to keep recording of telephone conversations within the guidelines of being legal. Once you have secured the "other party's" permission to record their conversation, then this circuit device built in a box is what you will need to have on "standby" the unit "beeps" every 10 seconds.

This will not require interfacing nor connecting to the phone lines as it is a stand-alone 9V unit which fits snugly within a plastic "Jiffy-Box" see "Jaycar" or "Altronics".

The law requires you to provide "beeps" every 10 seconds while you are recording both parties ie: you and the person you have called conversations. Any 8-ohm mW speaker will do. Electronic Decision Maker circuit. Figure 13 above Basically it's a Yes or No decision maker, a novel use of a NE for use when you can't make up your mind yourself and to have a little bit of fun with.

You could also use it as an executive decision maker. To Fire an employee or not to fire them. It can also be used as a "game" heads or tails whereas, pressing the SW-2 button will result in an either heads or a tails indication, it's up to you to pick and some have fun along the way and in the process and learn about electronics.

Have loads of fun at parties. The decision is yours to do with as you please. Enjoy, have fun with your electronics projects, that's what it's all about! The frequency for either output can be easily calculated by the following simple formula : Note: In reality, the output frequency will display on your CRO as 1 Hz, based on the applied maths. The circuit maths suggests that a 1K pot can be used, however some are found to be 1.

The addition of a Ohm resistor in series with VR1 could make all the difference! Above This will require a re-design of this circuit to comply with CMOS.

The yellow or 'pulse' LED comes on for approximately milli Seconds to indicate a pulse without any regard to its pulse width.

This feature enables one to observe a short-duration pulse that would otherwise not be seen on the logic 1 and 0 LED's. A small sub-miniature slider switch SW-2 across the R8 22K resistor with a ohm R7 to limit the current to pins 6 and 7 can be used to keep this "pulse" LED feature on permanent enough after a "pulse" occurs to confirm the existence of the pulse.

With the switch SW-2 closed, the circuit will indicate whether a negative-going or positive-going pulse has occurred. If the pulse is positive-going, both the ' 0 ' and 'pulse' LED's will be on. If the pulse is negative-going, the ' 1 ' and 'pulse' LED's will be on. The sequentially makes 1-of outputs high while others stay in a "low" state in response to inward clock pulses. Many applications count on the The actual counting occurs when pin 13 and 15 are low logic level. Switch SW-2 is used to reset or activate and run the timers.

Try different types of LDR's and.. Do not exceed this as it will smoke-up! Smoke is not a good look. A 9-volt Alkaline battery is usually a good general choice. Primarily it was used to test 90 Volt neons where "The Tester's Safety" is a high requirement. Often in industry, we need to make choices as to what an employee can and cannot use in full safety in the workplace, this is one such battery powered device. This is enshrined in industrial relations and in law. The R1 - R2 - C1 circuit determines the output oscillation frequency of the NE, thus producing a voltage at Pin 3 , just high enough to power into the small 8 ohm transformer's primary windings, the secondary windings are 1K ohms.

Thus testing any 90 Volts neon. This results in a ratio of about times gain, however we all know based on the maths, that's not going to fly. What about the Losses? The "theoretical voltage" of around Volts AC passing through R3 10K dropping to around V AC is thus just enough to strike the gas within the neon and therefore lighting it enough to detect whether the neon is a goer or just a bit of glass.

It is not designed for continuous usage but as a " go or no-go tester ", easily fitted into a small plastic box and power it by a 9 V battery and very portable.

User friendly. Virtually any brand of NE may be used here. The NE is a phased-locked loop chip. Check the data sheets for your infra-red LED as the current requirements will vary from manufacturer to manufacturer. You may need to increase the "R2" value to 22 ohms or more based on the operation current of the I. The circuit is designed for security use where an inconspicuous infra-red LED beam is needed. It is open to you for experimentation. SETTING UP : Setting up is relatively easy, with power applied to the receiver portion, gently turn VR1 on the Transmitter board until the relay clicks chatters and operates fully and becomes as a fully latched-on mode.

Be patient, this latching may take up to 2 seconds. We suggest using a small plastic "tube" perhaps with a small lens on the Photo-Transistor part to direct the incoming infra-red beam directly into the tube to achieve the best results. Line both the tubes up for best results, this task will require two persons. Please experiment with the same "tube" concept on the transmitter end as this will make the devices respond to directional infra-red input rather than a "splatter" of I.

Note: operating at lower frequencies affects latching times, making them slower. Diodes D2 and D3 provide the feedback logic 1 pulse to Pin 4 reset of the Electro-Motive Force or the collapsing coil voltage by diode 1N D1 which is rated at Volts at 1 amp. The back E. Applications: This circuit was designed for Security use or Vehicle breakdown dual lamp use where needed.

Cop cars? So simple, why did we not use it before? It uses only one resistor and one capacitor. For the purpose of the simplicity in display, we have "left off" the 0. It still functions acceptably. The circuit draws very little current from the supply due to the exclusive use of the NXP Philips ICM timer IC, however the frequency of operation will in fact be somewhat lower than a dual resistor circuits as describe in many other circuits on these pages.

This lower frequency is mostly due to the fact that the voltage delivered by the output line from Pin 3 is about 1. The output is still capable of driving up to mA. Don't exceed this. You may destroy your chip! Observe it on a CRO. Most circuits run very well at 15 V DC all day. This circuit was designed to use for "reasonably" good square wave output formations. Static electricity aside yes, someone will point out that there are no protection zener diodes on the transistor's input and rightfully so.

However, it is drawn for simplicity. You may add zeners as you wish tothe touch plate to protect the base of the 2N NPN transistor, thus protecting it somewhat. It is sensitive enough to pick up stray voltages such as static electricity and induce mains radiation picked up by our bodies. It can be "improved-on" by the addition of a second pad connected to ground which will enhance its operation.

We believe Edison found 10, ways not to make a light bulb and one that worked. A monostable has one stable state and that is the OFF state. Put simply, the monostable circuit generates a single fixed duration pulse during each time it receives its input trigger pulse. This type of circuit can be used for many switching applications, activating an external device for a specific length of time.

They can also be used to generate timed delays. The simple diagram below shows a push-button on left connected to a NE When this push-button is pressed, you will note that a relay has been added to Pin 3 output the relay operates for about 5 seconds.

The button must be released before the time-interval has expired otherwise the time is extended, so please note that this is a "limitation" of this simple circuit.

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

That causes the output to switch low.


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