Simple Triangular Wave Oscillator Circuit Diagram

This design resulted from the need for a partial replacement of the well-known 8038 chip,  which is no longer in production and there fore hardly obtainable. 

An existing design for driving an LVDT sensor (Linear Variable Differential Transformer),  where the 8038 was used as a variable sine  wave oscillator, had to be modernised. It may  have been possible to replace the 8038 with an  Exar 2206, except that this chip couldn’t be used  with the supply voltage used. For this reason we  looked for a replacement using standard components, which should always be available. 

Simple Triangular Wave Oscillator Circuit Diagram

Triangular Wave Oscillator Circuit Diagram

In this circuit two opamps from a TL074 (IC1.A  and B) are used to generate a triangular wave,  which can be set to a wide range of frequencies using P1. The following differential amplifier using T1 and T2 is configured in such a way  that the triangular waveform is converted into  a reasonably looking sinusoidal waveform. P2  is used to adjust the distortion to a minimum. 

The third opamp (IC1.C) is configured as a  difference amplifier, which presents the sine  wave at its output. This signal is then buffered by the last opamp (IC1.D). Any offset at the  output can be nulled using P3.

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Dice With 7-Segment Display Circuit Diagram

A digital dice circuit can be easily realised using an astable oscillator circuit followed by a counter, display driver and a display. Here we have used a timer NE555 as an astable oscillator with a frequency of about 100 Hz. Decade counter IC CD4026 or CD4033 (which-ever available) can be used as counter-cum-display driver. When using CD4026, pin 14 (cascading output) is to be left unused (open), but in case of CD4033, pin 14 serves as lamp test pin and the same is to be grounded.

Dice With 7-Segment Display Circuit diagram

The circuit uses only a handful of components. Its power consumption is also quite low because of use of CMOS ICs, and hence it is well suited for battery operation. In this circuit two tactile switches S1 and S2 have been pro-vided. While switch S2 is used for initial resetting of the display to ‘0,’ depression of S1 simulates throwing of the dice by a player. 

When battery is connected to the circuit, the counter and display section around IC2 (CD4026/4033) is energised and the display would normally show ‘0’, as no clock input is available. Should the display show any other decimal digit, you may press re-set switch S2 so that display shows ‘0’. To simulate throwing of dice, the player has to press switch S1, briefly. This ex-tends the supply to the astable oscillator configured around IC1 as well as capacitor C1 (through resistor R1), which charges to the battery voltage. Thus even after switch S1 is released, the astable circuit around IC1 keeps producing the clock until capacitor C1 discharges sufficiently. Thus for du-ration of depression of switch S1 and discharge of capacitor C1 thereafter, clock pulses are produced by IC1 and applied to clock pin 1 of counter IC2, whose count advances at a frequency of 100 Hz until C1 discharges sufficiently to deactivate IC1. 

When the oscillations from IC1 stop, the last (random) count in counter IC2 can be viewed on the 7-segment display. This count would normally lie between 0 and 6, since at the leading edge of every 7th clock pulse, the counter is reset to zero. This is achieved as follows. 

Observe the behavior of ‘b’ segment output in the Table. On reset, at count 0 until count 4, the segment ‘b’ output is high. At count 5 it changes to low level and remains so during count 6. However, at start of count 7, the output goes from low to high state. A differentiated sharp high pulse through C-R combination of C4-R5 is applied to reset pin 15 of IC2 to reset the output to ‘0’ for a fraction of a pulse period (which is not visible on the 7-segment display). Thus, if the clock stops at seventh count, the display will read zero. There is a probability of one chance in seven that display would show ‘0.’ In such a situation, the concerned player is given an-other chance until the display is non-zero. 

Note.  Although it is quite feasible to inhibit display of ‘0’ and advance the counter by ‘1,’ the same makes the circuit somewhat complex and there-fore such a modification has not been attempted.

Author : EFY LAb – Copyright : EFY

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Micropower Crystal Oscillator Circuuit Diagram

Crystal oscillators for digital circuits are normally built as Pierce oscillators with an inverter.The inverter operates as a linear amplifier and thus requires extra current. But you can also build a crystal oscillator using an  operational amplifier (op amp for short)! If a  very low frequency is involved, for instance  32.768 kHz (commonly used for clocks), you can get away with a comparatively ‘slow’ micro power op amp. 

Circuit diagram :

Micropower Crystal Oscillator Circuit Diagram

 

In the sample circuit shown a widely avail-able TLC271 is used. On pin 8 we have the  opportunity to set the ‘bias mode’, with three  choices ranging between fast operation with  higher current consumption and slower operation at low current. For our clock crystal the middle setting will suit us fine. Pin 8 is there-fore connected to the voltage divider R1/R2. The current consumption of the entire circuit  is impressively modest and at 5 V this is just  56 µA! The oscillator also functions astoundingly well at 3.3 V. At the same time the cur-rent drops to a more battery-friendly 41 µA. A  prototype built in the Elektor Labs produced  the slightly higher values indicated in the circuit diagram. 

The output signal delivered by this circuit has  admittedly scant similarity to a square wave.  Nevertheless some cosmetic surgery will tidy  this up, with treatment in the Schmitt trigger  following. To save current (naturally) we use  a CMOS device such as the 74HC14. 

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Baud Rate Generator Circuit Diagram

In this article, an RC oscillator is used as a baud rate generator. If you can calibrate the frequency of such a circuit sufficiently accurately (within a few percent) using a frequency meter, it will work very well. However, it may well drift a bit after some time, and then…. Consequently, here we present a small crystal-controlled oscillator. If you start with a crystal frequency of 2.45765 MHz and divide it by multiples of 2, you can very nicely obtain the well-known baud rates of 9600, 4800, 2400, 600, 300, 150 and 75. If you look closely at this series, you will see that 1200 baud is missing, since divider in the 4060 has no Q10 output!

Baud Rate Generator Circuit Diagram

If you do not need 1200 baud, this is not a problem. However, seeing that 1200 baud is used in practice more often than 600 baud, we have put a divide-by-two stage in the circuit after the 4060, in the form of a 74HC74 flip-flop. This yields a similar series of baud rates, in which 600 baud is missing. The trimmer is for the calibration purists; a 33 pF capacitor will usually provide sufficient accuracy. The current consumption of this circuit is very low (around 1mA), thanks to the use of CMOS components. 

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1:800 Oscillator

Oscillators are ten a penny, but this one has something special. Its frequency can be adjusted over a range of 800:1, it is voltage controlled, and it switches off automatically if the control voltage is less than approximately 0.6 V. As can be seen from the chart, the characteristic curve f = f(Ue) is approximately logarithmic. If the input voltage is less than 0.7 V, T1 and T3 are cut off. The capacitor then charges via the 10-kW resistor. The combination of the capacitor, the two Schmitt triggers and T2 form the actual oscillator circuit. However, T2 cannot discharge the capacitor, because T3 is cut off.

In this state, a low level is present at A1 and a high level is present at A2. If the input voltage is increased, T3 starts conducting. This allows the capacitor to be discharged via T2, and the circuit starts to oscillate. If Ue is further increased, the capacitor receives an additional charging current via T1 and the l00-Ω resistor. That causes the oscillator frequency to increase. In situations where the duty cycle of the output signal is not important (such as when the circuit is used as a clock generator), this circuit can be used as a voltage-controlled oscillator (VCO) with a large frequency range and shutdown capability. 

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50 to 300 MHz Colpitts Oscillator Circuit Diagram

Simple high efficiency Colpitts oscillator .In the higher frequency ranges, above 50 MHz, Colpitts oscillators are used because stray circuit capacitance will be in parallel with desired feedback capacitance and not cause undesirable spurious resonances that might occur with the tapped coil Hartley design.

50 to 300 MHz Colpitts Oscillator Circuit Diagram

The FM VCO shown is a grounded base design with feedback from collector to emitter. A Colpitts oscillator is one of a number of designs for electronic oscillator circuits using the combination of an inductance with a capacitor for frequency determination.As you can see in the circuit diagram , this electronic project require few electronic parts an provide a 50 MHz-300MHz VCO with a tuning range of 2:1 . link

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MHz Oscillator using an ATtiny15 Schematic

Most engineers will recognise the problem: Your circuit needs a stable 1 or 2 MHz clock generator (in the author’s case it was for a Pong game using an old AY3-8500). A suitable crystal is not to hand so you cobble together an RC oscillator (there are plenty of circuits for such a design). Now it turns out that you don’t have exactly the right capacitor so a preset pot is add e d to allow some adjustment . Before you know it the clock circuit is taking up more space on the board than you had hoped. 

Providing the application does not demand a precise clock source a tiny 8-pin microcontroller may offer a better solution to the problem. It needs no additional external components and an old ATtiny15 can be found quite cheaply. Another advantage of the solution is that clock frequency adjustment does not involve changing external components and is not subject to component tolerances. 

The microcontroller’s internal RC oscillator is already accurately calibrated to 1.6 MHz. With its inbuilt PLL, internal Timer 1 can achieve up to 25.6 MHz [2]. By configuring internal dividers the timer can output a frequency in range of roughly 50 kHz up to 12 MHz from an output pin. The difference between calculated and the actual output frequency increases at higher frequencies. A meaningful upper limit of about 2 MHz is a practical value and even at this frequency the deviation from the calculated value is about 15 %.

MHz Oscillator using an ATtiny15 Schematic

The circuit diagram could hardly be simpler, aside from the power supply connections the output signal on pin 6 (PB1) is the only other connection necessary.The example program, written in Assembler is just 15 lines long! With a program this short comments are almost super fluous but are included for clarity. The code can be downloaded from the Elektor website [1]. 

The program only needs to initialise the timer which then runs independently of processor control to output the clock sign al . The processor can then be put into sleep mode to memory used up the remaining 99 % is free for use for other tasks if required. 

The OSCCAL register contains a calibration byte which allows some adjustment of the CPU clock. This gives a certain degree of fine tuning of the output frequency. A recommendation in the Atmel data sheet indicates that the CPU clock frequency should not be greater than 1.75 MHz otherwise timer operation cannot be guaranteed. 

The more recent ATtiny45 can be substituted for the ATtiny15. In this case the CK SEL fuses should be set to put the chip’s Timer 1 into ATtiny15- compatible mode [3]. After adjustment to the program it will now be possible to obtain a higher (or more exact) frequency from the timer, the ATtiny45’s PLL can operate up to 64 MHz.  Link

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Triangle Square Wave Oscillator Circuit Diagram

By making Rt variable it is possible to alter the operating frequency over a 100 to 1 range. Versatile triangle/squarenvave oscillator has a possible frequency range of 0 Hz to 100 kHz.

Simple Triangle Square Wave Oscillator Circuit Diagram

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