First is, Lower comparator becomes HIGH and Flip flop gets Set and we get HIGH OUTPUT at PIN 3.We know that Non-inverting end of Lower Comparator is at 1/3Vcc, so when we apply negative (< 1/3Vcc) voltage to the Trigger PIN 2 by connecting it to Ground (through a PUSH button switch), two things happens: Operation is simple, initially 555 is in stable state i.e. So here we are explaining the Monostable mode of 555 Timer IC.īelow is the Internal structure of 555 Timer IC: If you want to learn the 555 IC in detail, check out our detailed 555 Timer IC article.ĥ55 Timer IC is configured in the Monostable mode for this Time Delay circuit. Power or VCC: It is connected to positive voltage (+3.6v to +15v). Whenever the output goes low or the flip-flop gets reset, the discharge pin is pulled to ground. DISCHARGE: This pin is drawn from the open collector of transistor. Since the transistor (on which discharge pin got taken, Q1) got its base connected to Qbar. Then a voltage equal to or greater than VCC*(2/3) (i.e.6V for a 9V supply) will reset the flip-flop. The threshold pin is drawn from positive input of comparator1. THRESHOLD: Threshold pin voltage determines when to reset the flip-flop in the timer. Normally this pin is pulled down with a capacitor (0.01uF), to avoid unwanted noise interference with the working. Control Pin: The control pin is connected from the negative input pin of comparator one. This pin is connected to VCC for the flip-flop to stop from hard resetting. Reset pin is directly connected to MR (Master Reset) of the flip-flop. Reset: There is a flip-flop in the timer chip. This is output pin where Load is connected. OUTPUT: This pin also has no special function. If this pin is connected to ground (or less than Vcc/3), the output will be always high. With the comparator two output high we get high voltage at the timer output. The comparator two output is connected to SET pin of flip-flop. TRIGGER: Trigger pin is dragged from the negative input of comparator two. Ground: This pin should be connected to ground. Below you can find the pin diagram of 555 timer IC along with the details of each pin. Required Components:īefore going into detail of Time Delay Circuit, first we need to learn about 555 Timer IC first. Also check our 1 minute timer circuit using 555. A 5v voltage regulator is used for giving 5v regular supply to the circuit. Here we have used 9 V battery and 5V optional relay for switching the AC load. It also has a potentiometer to adjust the time delay, where you can increase of decrease the time delay by just rotating the potentiometer. This circuit consists of 2 switches one for start the delay time and other for reset. In this project we are going to design a Simple Time Delay Circuit Using 555 Timer IC.

Stm32 simple delay