Tag Archive: Oscillator


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  The following CD4017 circuits have not been tested and is presented here as a possibility only. If you experiment with this circuit, please send me any problems found so that the circuit can be updated.

  The following circuits are designed to change the duration of each positive output pulse from the astable timer. The circuits use a CD4017 Decade Counter / Decoder to provide nine or ten steps in the cycle.

  The first circuit operates with a repeating ten step cycle. Each output pulse is longer than the previous until a count of ten is reached at which time the cycle will repeat.

  The second circuit has a nine step cycle that stops at the end of the cycle. The cycle is restarted or reset when the RESET input is briefly made high.

  The CD4017 can be configured to give count lengths between 1 and 10. Refer to the timing diagram in the CD4017 data sheet for a better understanding of the IC’s operation.

6N137 Connection Diagram

Image6N137 Connection Diagram
A simple voltage-controlled oscillator (VCO), coupled to your instrumentation by an optoisolator, allows you to measure high voltages. The component values suit a 0- to 600-V input range (power dissipation in R1 and R2 set a limit on the input-voltage range). The circuit’s linearity is not an issue, because you can linearize its output in software.

The input voltage (V1), charges capacitor C1 until zener diode D1 conducts. Then, the zener diode triggers an “avalanche” circuit that discharges C1 into optocoupler Q1. After C1 discharges, the charging cycle repeats. C1 also averages the sensed-voltage level, which thereby provides noise immunity.

The optocoupler’s output is a pulse train whose frequency increases with increasing input voltage. To develop a linearizing equation for the circuit, measure its output at two convenient, widely spaced input voltages. Then plug the resulting periods into this second-order polynomial approximation and solve the two simultaneous equations for the two constants, k1 and k2:
 
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Vz is the zener voltage of D1.

LM311 is a comparator, It operates from single 5V supply or dual supplies,input current 150 nA, 50 V-50 mA output drive capability. TTL-CMOS compatible output.

The Output is open collector so it can sink current but cannot source, a totem pole output can source and sink. In this Circuit R2 is the source or pull-up.

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The Output being high or low depends on which input is more dominant or positive. If + or non-inverting input is more positive than the – inverting input then output of LM311 is high impedance or high Z as output transistor of LM311 is turned off, but output goes high due to R2 pull-up 1K, so you can apply a load of 10K and above for source. When the – input or inverting input is more positive, output goes Low as transistor turns on, now a current of upto 50mA can sink here, a LED or Relay can be driven.

On turn on C2 capacitor is discharged and pin 3 the inverting input is at a lower potential than pin 2 the non-inverting which is at 2.5V. Hence output goes high and C2 starts charging thru R5, When C2 charges a little beyond 2.5V pin 3 is more dominant and output goes low now, this slowly discharges the C2 bringing the voltage at pin 3 again below 2.5V so output goes high again. This process goes on, hence it oscillates. The charging and discharging is at the rate of R5 * C2 approx. , R3 serves as hysteresis or feedback to ensure clean turn on and off.

TDA7000 FM Receiver / TV Tuner

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This simple one chip FM receiver / TV tuner will allow you to receive frequencies from 70 up to 120MHz. With this small receiver it is possible to pickup TV stations, entire 88 – 108MHz FM band, aircraft conversation and many other private transmissions. It is a perfect companion to any FM Transmitter especially if FM band in your area is very crowded. TDA7000 receiver offers very good sensitivity therefore it will even allow you to pickup weaker signals that cannot be heard on conventional FM receivers.

A neat feature of presented TDA7000 FM receiver is a voltage controlled oscillator similar to TV tuners that are used in television sets. Frequency is tuned by varying the input voltage to the oscillator. The advantage of this type of oscillator is that you can use regular 100K potentiometer to precisely tune to a given broadcast. Tuning can be performed much quicker and precisely than by using a trimmer (variable capacitor). Trimmers will also shift the frequency as you touch them where potentiometer will not. Trimmer also needs to be placed on receiver’s PCB to minimize the stray capacitance where potentiometer can be conveniently placed anywhere you want because it will not be affected by any external capacitance.

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LM311 is a comparator, It operates from single 5V supply or dual supplies,input current 150 nA, 50 V-50 mA output drive capability. TTL-CMOS compatible output.

The Output is open collector so it can sink current but cannot source, a totem pole output can source and sink. In this Circuit R2 is the source or pull-up.

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The Output being high or low depends on which input is more dominant or positive. If + or non-inverting input is more positive than the – inverting input then output of LM311 is high impedance or high Z as output transistor of LM311 is turned off, but output goes high due to R2 pull-up 1K, so you can apply a load of 10K and above for source. When the – input or inverting input is more positive, output goes Low as transistor turns on, now a current of upto 50mA can sink here, a LED or Relay can be driven.

On turn on C2 capacitor is discharged and pin 3 the inverting input is at a lower potential than pin 2 the non-inverting which is at 2.5V. Hence output goes high and C2 starts charging thru R5, When C2 charges a little beyond 2.5V pin 3 is more dominant and output goes low now, this slowly discharges the C2 bringing the voltage at pin 3 again below 2.5V so output goes high again. This process goes on, hence it oscillates. The charging and discharging is at the rate of R5 * C2 approx. , R3 serves as hysteresis or feedback to ensure clean turn on and off.