Can someone please help me understand how these work.
In the first one the diode zener and 100k create a voltage of 3.3v. The voltage on the the 200ohm resistor is 3.3-0.7v (0.7v -voltage on the transistor)
Ie=Ic so that the elec current on the capasitor is 2.6v/200ohm.
The cap is charged and when it reaches 2/3Vcc it discharges (because of the transistor in leg 7 of the 555 timer). When it reaches 1/3 Vcc it is charged again and the same thing is repeated. So what do you get for the output of the 555 timer. Usually the trigger is a seperate pulse but this time it's connected to the 6th and 7th legs. Also how do I calculate the time of the output pulse t=r*c?
In the second one it looks like the same thing except without the diode zener. What is the function of the opamp at the bottom?