Frequency Divider 74HCT4040

 555-Circuits, Digital-Circuits  No Responses »
Nov 062004
 
Frequency Divider 74HCT4040

U1 7555 is a CMOS version of 555. The 555 here is in Astable Oscillator mode, C1 and C4 are decoupling capacitors 0.1uF value, ceramic disc. The output is around 100kHz, If C3 is plastic or mica the frequency output will be stable with temperature. It is better to use a crystal oscillator. The 555 output is fed to clock input of 4040, the output of 555 will be a square wave, on every high to low transition (falling edge or negative transition) the counter increments by one and the output is 12 bit binary. If input frequency is F Read More …

 Posted by admin at 5:15 AM

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 admin at 5:15 AM  Tagged with:

Differential to TTL convertor using LM339

 Digital-Circuits  1 Response »
Oct 292004
 
Differential to TTL convertor using LM339

Some outputs are via Dual Differential Line Driver type DS8830. This device will interface with standard TTL systems. The differential outputs are balanced and are designed to drive long lengths of coaxial cable, strip line, or twisted pair transmission lines with characteristic impedances of 50 ohms to 500 ohms. Differential transmission is superior to single wire transmission in that it nullifies the effects of ground shifts and noise signals which appear as common mode voltages on the transmission line. If the signal voltage at the end of the line is found to be of insufficient magnitude then the following circuit Read More …

 Posted by admin at 8:18 PM

Simple Digital Event Counter

 Digital-Circuits  No Responses »
Oct 292004
 
Simple Digital Event Counter

The basic digital circuits are Flip Flop and Counter, both are here. This circuit can be cascaded to make even a 6 digit event counter, even a simple frequency counter can be made. These are best done with microcontrollers today. Then what if you have to design your own microcontroller on a FPGA, so the basics have to be sound, hence you have to know what gates, flip flops and counters are. see the seven segment display. Inc, Dec, and Set buttons are momentary acting and Clk Button is latching type. The Dip Switch in the also can be set. Read More …

 Posted by admin at 8:06 PM

Running Lights with CD4017

 555-Circuits, Digital-Circuits, LED-Circuits  No Responses »
Oct 292004
 
Running Lights with CD4017

The 555 Astable generates a clock for this circuit, an oscillator giving a square wave output at pin 3 which is counted by 4017 to give a running lights effect. The decade counter-divider CD4017 has 10 outputs, for every low to high transition at the clock input, rising edge, the counter advances one LED. After going one full circle the the first LED lights again and it goes on. You can vary the value of R2 100K Linear potentiometer to make LEDs run fast or slow. The frequency of oscillation of astable 555 is given as f = 1.44 / Read More …

 Posted by admin at 11:27 AM

OR gate with two 555

 555-Circuits, Digital-Circuits  No Responses »
Oct 232004
 
OR gate with two 555

This shows how to OR gate two 555, when one 555 cycles at a low frequency a valve turns on an off, the second 555 stretches the ON duration of the pulse with a diode OR gate. The OR output uses sample and hold to get the stable analog data from a sensor after the actuator has gone OFF, this ensures correct reading. 555 is a fundamental Mixed Signal Circuit as it can be made into a VCO using Pin-5. If you see old exar databooks, you can see 555 and PLL and Tone decoders all applications compiled in one Read More …

 Posted by admin at 12:30 PM
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