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Astable Multivibrator with 555 Timer

This is a demo of the popular 555 timer. you can try out the project on this page by a javascript simulation. Press the Red button below to turn on the circuit press it again to turn off. The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback.Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.

This is a tutorial with calculator to help learn the application of 555 which is a very rare chip innovation. It is simple, versatile, flexible and programmable (by tweaking of pots).

Astable 555 Timer Flasher – Interactive demo

The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high.

The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.

Astable Multivibrator with 555 Timer

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VCO with LM331

This Circuit is a simple Analog to Digital Interface with a capability of 10 to 12 bits resolution. 10 bits means 1024 counts or parts of a full scale FS which is close to 3-1/2 1999 counts.

VCO with LM331

In this 1 V can be read as 1.000 V that means even 1mV can be resolved for FS of 1V. The Caps C6 and others must be plastic multilayer low-leakage types for accuracy of reading. Use all 1% MFR 100ppm or better resistors, Design gain of U1B for the Full Scale you want.

Mixed Circuits Analog with Digital

The Output Fout is a Frequency which is directly proportional to the measured voltage Vin. The pulses can be isolated using opto-couplers to avoid ground loops or electric hazard. An additional protection and scaling circuit at the input may be required for some sensors.

1 Hz or 1 PPS Crystal Clock Base

The CD4020BC, CD4060BC are 14-stage ripple carry binary counters, and the CD4040BC is a 12-stage ripple carry binary counter. The counters are advanced one count on the negative transition of each clock pulse. The counters are reset to the zero state by a logical “1” at the reset input independent of clock.

CD4040BC, 12-Stage Ripple Carry Binary Counters
CD4060BC, 14-Stage Ripple Carry Binary Counters

1 Hz or 1 PPS Crystal Clock Base

CD4060 – 14-Stage Ripple Carry Binary Counters

you can also use a crystal between pin 10 and 11 with two caps 22pF from 10, 11 to gnd and a 10M resistor between 10 and 11 in place of R C network for more precision.

Crystal Oscillator – Parallel Resonant

74HCU04 is a chip that was made for this purpose, HCT may not work for such a circuit. C1 and C2 can go to upto 33pF and R2 can be increased to make R2 * C2 = t.

Crystal Oscillator - Parallel Resonant


Time constant much less than the period T of the crystal T = 1/F . This is to remove higher frequency components in the Oscillator.

More on Piezoelectric Crystal Oscillator

The circuit above is a parallel resonant oscillator circuit. The Crystal works by the piezoelectric principle, piezo means pressure. The electric field causes the impedance of the crystal to change. The LP Record Player needle is the reverse of this, the bumps on the spiral groove of the record applies pressure to needle which generates electricity. Both are piezo-electric effects.

Analog Blind Dial On Delay Timer

It is called analog dial timer as it has no digital display, but the chip is digital it is CD4541. It is Mains operated, you could make on-delay or off-delay. By changing the caps and resistors or with even dip-switches you could get timing of few seconds to many hours. Circuit is Analog Timer 4541 .

Analog Blind Dial On Delay Timer

Some timers energize the relay after a set delay on power start. Some start with relay energized and turn off after set time. Motors and big systems cannot take fast turn-on and turn-off, Some systems will require sections or modules to start one after another as they are interdependent. So Timers in automation were made to effect such delays, the early ones were mechanical clockwork.

Analog Timer

The CD4541BC Programmable Timer is designed with a 16-stage binary counter, an integrated oscillator for use with an external capacitor and two resistors, output control logic, and a special power-on reset circuit. The special features of the power-on reset circuit are first, no additional static power consumption and second, the part functions across the full voltage range (3V¨C15V) whether power-on reset is enabled or disabled.

  • Available division ratios 28, 210, 213, or 216.
  • Increments on positive edge clock transitions.
  • Built-in low power RC oscillator.
  • Oscillator frequency range . DC to 100 kHz.
  • Power on Auto reset initializes all counters.

PLL using 4046 – Phase Locked Loop

CD4046 is a PLL or phase lock loop, it mainly consists of a VCO and phase comparators. This is a component in FM demodulation and modulation.

Mixed and Interface Circuits

PLL using 4046

It is used in a closed loop control to maintain a stable frequency. The Circuit above is good for learning the full use of a small Dual Trace Scope. The Circuit has both Analog and Digital areas and is a part of communication.

Read the pages above for building more Knowledge on PLL

LM311 Square Triangle Oscillator for PWM

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.

Even LM324  used as a  comparator Water Level Indicator with Reed Relays

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.

LM311 Square Triangle Oscillator for PWM

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.

Mixed Circuits Analog with Digital

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.