Crystal Oscillator – Parallel Resonant

 Digital-Circuits, Embedded-Systems  No Responses »
Nov 062004
 
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. Time constant much less than the period T of the crystal T = 1/F . This is to remove higher frequency components in the 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 Read More …

 Posted by at 5:15 AM  Tagged with:

Astable Multivibrator with 555 Timer

 555-Circuits  No Responses »
Oct 292004
 
Astable Multivibrator with 555 Timer

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. de_gads_top 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. These are the formulae used by 555 . T1 = 0.693 (Ra + Rb) * Ct charge time of Ct T2 = 0.693 (Rb * Read More …

 Posted by at 7:39 PM  Tagged with:

Isolated dual power supply from 5V

 Discrete-Circuits, Power-Supplies  No Responses »
Oct 272004
 
Isolated dual power supply from 5V

This is a unregulated supply for low power circuits. You may be able to regulate the outputs with zeners or small regulators like 78L05. The transformer can be hand wound in a mini ferrite pot core. you can use 2N2222 or any other fast transistor. The transformer should have 1KV isolation. The dot polarity of TR1 should be properly observed, else it may fail to oscillate or give output. Diode should be fast recovery type, for less than 100mA use 1N4148. transformer, pri-20-20, sec-60-60, a SWG-AWG to suit the current you design for, any fast switching transistor would work, no Read More …

 Posted by at 10:01 PM  Tagged with:

Fixed frequency Variable duty cycle with 555

 555-Circuits, Mixed-Circuits  No Responses »
Oct 232004
 
Fixed frequency Variable duty cycle with 555

This circuit is based on a very old application note from exar, in this the frequency is fixed by IC1 and IC2 -P1 controls the duty cycle. you need to compute the R and C values to get what you need, LM555 data sheet. You have to study the circuit and do something more innovative perhaps, just copying is ok for learning but it will get you nowhere, so learn and then innovate, the eagle circuit is given below so you can learn by editing it, also design a PCB with it, and you can even make a PCB at Read More …

 Posted by at 12:28 PM  Tagged with:
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