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555 based Reset Generator

You must have read all the circuits and explanation on the other pages at delabs to understand this, as i cannot repeat the same thing as i have done it more than once already.

The circuit is a 555 monostable, The push-switch is to trigger and generate a reset pulse for uC. The diode is for OR’ ing later. The High will go thru the diode but the Low of 555 cannot drink any current as diode blocks.

555 based Reset Generator

The bottom part of the Circuit is the CD4093 Schmitt nand based flipflop. See more at 555 Timer based Circuits

What is the Schmitt then ?, It is better to visit the links below to learn. It can make a sine or triangle or any shape waveform to square. It can help square a very messy waveform.

Two nand gates are connected to form a flip-flop toggle switch. When 555 gives out a pulse, the pulse is delayed by a R-C which results in a ramp, the third nand-Schmitt gives out delayed low trigger to toggle nand-flipflop-switch. The Nand-toggle-switch is rest at any time with the lower pushbutton. The fourth nand output gate is not really required. But the 4093 is quad nand, so unused nand inputs should not float , pull-up or pull-down. So it has just been added in circuit so that he can fit some role, or else he will be bored.

Now you can figure out how such blocks can be used like Lego blocks in your own amazing designs.

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.