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.
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.
IC1 astable gives a fixed square wave at pin 3, C1 and R1 derive uS trigger pulses from IC1 and this will trigger IC2 monostable or single shot, the voltage at pin 5 of IC2 will change the pulse width output of IC2, to get it working all the three RC combinations have to be figured out.
Optical Obstacle Switch.
You can even build a small SMPS with this or even control the temperature of your soldering iron using the SSR solid state relay circuits in power section, then you need to think and design the cycle time of a soldering iron heat control system, it will be in seconds but then above circuit is running at audio frequencies, then you have to work that out yourself..
CD4538 is a dual Monostable Multivibrator. When you trigger the chip the output sends off one single pulse or one high-low event.
Mixed Circuits Analog with Digital
The T+ pin 4 of U1a is the positive edge trigger or raising edge trigger input, the T- pin 5 is falling edge or negative edge trigger input. Now see the image of the single pulse above which shows both the edges, If this is the input pulse at pin 5 then the falling edge turns the output pin 6 from low to high, this output remains high for time T = R2 * C1 and then goes low again, The output Q at pin 6 also looks like the image of pulse above.
The Output pin 7 is the complementary state of pin 6, it is the reverse state or inverted form of pin 6 output.
Now why is a slope shown in the edges, this i have exaggerated a bit so that it can be explained. But then there is a slight slope due to gate input and output capacitance.
In fact if you had a wire or twisted track coming to the input and the R2C1 was in nano seconds, then you would see a ringing at the edges, a tiny peak or spike, which will have giga hertz frequency components, in fact a square way may be many sine waves put together, this you know from a spectrum analyzer.
Two Stage Sequential Timer
CD4538B can give an output with pulse width of 1uS and above. 74HC4538 gives 120nS to 60 Seconds pulses. The above circuit produces a pulse of width T = R3 * C2 after a delay of T = R2 * C1. Some Chips formula is T = 0.7 * R * C .
This is related to the earlier post. This was done to save battery power. The output of some equipment may be in the form of LED Annunciators In the Security Guard Monitor, an Array of 24 LEDs would show the Status of alertness along with the day, this was scrollable.
When the “Display Now” is pressed it triggers the Monostable Multivibrator made of a 555. The output “EN” goes high for the time duration defined by C27 and R71.
The 555 output as you know can drive more than 200mA for quite some time without much heating up. Many LEDs can be driven with the current limit resistors. I used CMOS chips to drive the LEDs, this circuit was used for the Logic only.
This circuit was a part of the user interface like the previous one. You could use it for voltmeters or even backlight for LCD.
Example – When you press the switch the Time of a clock can be seen in darkness for a few seconds.