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Simple but high efficiency of this circuit is a Colpitts oscillator for VHF. Ideal for higher frequencies above 50 MHz, Colpitts oscillators are used for VHF parasitic capacitance of the circuit is in parallel with the feedback capacitance desired and causes no undesired spurious resonances which may occur with the Hartley oscillator. The circuit above is a VCO FM, it is a grassroots project with grounded feedback from collector to emitter. A Colpitts oscillator is a series of designs for electronic oscillator circuits using a combination of an inductance with a capacitor to determine the frequency. Make an Oscillator 50-300 MHz Colpitts Type Circuits Diagram

Tiny  Metronome Circuits Diagram Notes: Q1 & Q2 provide linear frequency operation of IC1 following P1 resistance variation. Q3 was added in order to obtain a louder click, similar to clockwork metronomes. A 12V micro battery was used to obtain a higher output power and more compactness. Rotate P1 fully towards R2, then set R1 to obtain 40 beats per minute (compare with another metronome). Rotate P1 fully towards R3, then set R4 to obtain 208 beats per minute. Finally mark the entire scale with the usual metronome steps, as follows: 40 - 42 - 44 - 46 - 48 - 50 - 52 - 54 - 58 - 60 - 63 - 66 - 69 - 72 - 76 - 80 - 84 - 88 - 92 - 96 - 100 - 104 - 108 - 112 - 116 - 120 - 126 - 132 - 138 - 144 - 152 - 160 - 168 - 176 - 184 - 192 - 200 - 208. Parts: P1______100K    Linear Potentiometer   R1_______10K    1/2W Trimmer Cermet R2_______10K    1/4W Resistor R3______330K    1/4W Resistor R4_______50K    1/2W Trimmer Cermet R5______100K...

Overview: The AN7171NK and AN7176K are ICs for power amplification of 14W (13.2V, 4Ω) output. It can provide stereo operation since two BTL amplifiers are incorporated in achip. It incorporates various protective circuits, thus providing high reliability. The circuits can be turned on or offwith supply pins energized, because the stand-by circuit is built-in. Circuit Diagram: Dual BTL 14W Audio Power Amplifier Circuits

555 timer tester is a simple circuit that serves to test the condition of IC 555. 555 timer circuit tester, in principle, start the timer 555 in astable multivibrator mode. As an indicator of the status of the timer 555 good condition or damaged to use 2 pieces LED which will light up in a blink alternately when the timer 555 in good condition. And only one will turn on or off all the timer 555 when the condition is broken. 555 timer circuit tester is powered using 9 Volt DC voltage source. Complete circuit tester 555 as follows.   How to use 555 timer tester is in conjuction with IC 555 to test the existing IC socket according to the order button. Then activate the power switch to begin testing the 555 timer ic. Then live we observe the LED indicators 2 before, whether flashing alternately (good) or not blink or even die all (timer 555 damaged). source:link

Normally analogue-to-digital converter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost. The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines. Usually the control signals EOC (end of conversion), SC (start conversion), ALE (address latch enable) and OE (output enable) are interfaced by means of a microprocessor. However, the circuit shown here is built to operate in its continuous mode without using any microprocessor. Therefore the input control signals...

The most simple polarity protection tehnique is to connect a series diode to the power line input. The diode conducts only when the power supply protection is correct. But the incovenient is that at higher current levels, the voltage drops and power loss of the diode affects the power level adversely. This polarity protection circuit is dimensioned for 12 V power supplies and avoids the voltage and power loss problem. By correct polarity, the current flowing to the D1 and the relay coil causes the relay contacts to activate. The NO contact closes powering the electronic device. The NC contact opens and the current supplying the relay coil is reduced to a low level just enough to maintain relay activation. source [link]

I’ve already shown how to drive an N-channel MOSFET (or even an IGBT) in both high-side and low-side configurations in a multitude of ways. I’ve also explained the principles of driving the MOSFETs in these configurations. The dedicated drivers I’ve shown so far are the TC427 and IR2110. Some people have requested me to write up on MOSFET drive using the very popular TLP250. And I’ll explain that here. The TLP250, like any driver, has an input stage, an output stage and a power supply connection. What’s special about the TLP250 is that the TLP250 is an optically isolated driver, meaning that the input and output are “optically isolated”. The isolation is optical – the input stage is an LED and the receiving output stage is light sensitive (think “photodetector”). Before delving any further, let’s look at the pin configuration and the truth table. Fig. 1 - TLP250 Pin Configuration Fig. 2 - TLP250 Truth Table Fig. 1 clearly shows the input LED side and the receiving photodetector as well...

Pyroelectric Fire Sensor -Circuit-Diagram. Here is an ultra-sensitive fire sensor that exploits the direct piezoelectric  property  of  an ordinary piezo element to detect fire. The lead  zirconate  titanate  crystals  in the piezo element has a property to de-form and generate an electric potential plifier with gate protected p-channel.  MOSFETs in the inputs. It has high speed  of  performance  and  low  input current requirements. There are two inputs—the non inverting input (pin 3) connected to the piezo element through diode D7 (OA71) that carries the volt-age signal from the piezo element and the inverting input (pin 2) that gets a momentarily changes the voltage level at pin 3 of IC1 and its output swings high. Transistor T1 conducts taking the reset pin 12 of IC2 to ground. IC2 is now enabled and start oscillating. With the shown values of the oscillating components C3 (0.22) and R8 (1M), when heated, thus converti...

This simple circuit generates a good 1KHz sine wave adopting the inverted Wain bridge configuration (C1-R3 & C2-R4). It features a variable output, low distortion and low output impedance in order to obtain good overload capability. A small filament bulb ensures a stable long term output amplitude waveform.  1KHz Sine wave Generator Circuits Diagram  Notes: The bulb must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term stability and low distortion. Distortion @ 1V RMS output is 0.15% using a 12V 40mA bulb, raising to 0.5% with a 12V 100mA one. Using a bulb differing from specifications may require a change of R6 value to 220 or 150 Ohms to ensure proper circuit's oscillation. Set R5 to read 1V RMS on an Audio Millivoltmeter connected to the output with R7 rotated fully clockwise, or to view a sinewave of 2.828V Peak-to-Peak amplitude on the oscilloscope. With C1, C2 = 100nF the frequency generated is 100Hz and with C1, C2 = 1nF frequency ...

Phone circuits are busy pointer. A busy signal is a signal that indicates that someone is trying to call a phone number but could not be contacted because the phone if it is not involved, or because the circuits are busy, calls are impossible to solve. On many phones, busy signals take the form of a distinctive tone, but a busy signal can also be visual, as in the case yanga phone designed for users of deafness or hearing impairment. Many people are familiar with a busy signal sounds, because significantly different from the dial tone, a tone that indicates that the phone line is open and ready to be called. In most cases, only a busy signal indicates that the person you are calling is a call. A busy signal will also sound when the phone is turned off. In this case, the signal indicates that there are no technical obstacles to placing the call, but calls can not be completed because the phone is in use. In some cases, you can ask the operator to enter, if you call in an emergency, in t...

As the name indicates , a sample and hold circuit is a circuit which samples an input signal and holds onto its last sampled value until the input is sampled again. Sample and hold circuits are commonly used in analogue to digital converts, communication circuits, PWM circuits etc. The circuit shown below is of a sample and hold circuit based on uA 741 opamp , n-channel E MOSFET BS170 and few passive components. Description As the name indicates , a sample and hold circuit is a circuit which samples an input signal and holds onto its last sampled value until the input is sampled again. Sample and hold circuits are commonly used in analogue to digital converts, communication circuits, PWM circuits etc. The circuit shown below is of a sample and hold circuit based on uA 741 opamp , n-channel E MOSFET BS170 and few passive components. In the circuit MOSFET BS170 (Q1) works as a switch while opamp uA741 is wired as a voltage follower. The signal to be sampled (Vin) is applied to the drai...

This circuit is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys. With SW1 positioned as shown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the old siren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1 that starts oscillation in IC1C and IC1D.  The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order to obtain a more realistic and louder output. Tone and period of the sound oscillations can be varied by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch is required: leave SW1 in the low position (old-type siren) and the circuit consumption will be negligible. Single -IC Dual-tones Siren Circuits Diagram Parts: R1 ,R3 ___470K    1/4W Resistors...