555 based Reset Generator - del50008

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 multivibrator like power oscillator

The bottom part of the Circuit is the CD4093 Schmitt nand based flipflop. Power on Soft Start with Reset.

 

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



Usage of Schmitt trigger NAND Gates

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.



RS Latch Erroneously setting by Itself

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

Trigger Voltage in 555

Trigger Voltage The pulse/level at pin 2 should drop below 1/3 Vcc before the timer triggers. This drives Output high for The RC period in a Monoshot. This is an analog input and just like the 2/3 Threshold Comparator is used to Turn the Output On/Off. 

Simple Timer

See the trigger pin 2 being used with a Switch to ground, a Green Button to start a timer. The timer output pin 3 goes high and turns on a Relay. The relay contacts could be used to drive a motor or lamp. In this configuration Pin 5 control voltage sets the time. When pin 3 goes high the pin 7 discharge goes into high impedance. Now C starts charging thru Ra. When 2/3 Vcc or 15V is reached (10V) across C; Pin 6 comparator senses it and changes the state of the internal Flip-Flop. The output goes low, Relay tuns off, pin 7 discharge turns on and discharges the cap C. Motor is off.

Now the timer is ready for the next cycle when you press start. Remember that when the Timer was on and the Motor was running; pressing reset would stop the motor prematurely. This would be the Red Button.

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