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how to build a 555 timer circuit for 5 seconds
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Adhith:
Hello everyone..
I'm working on making a simple 555 timer circuit to power another circuit for one of my project. The timer should be on only for the first 5 seconds and then should be off for the rest of the operation. during the on time it should drive a mechanical relay and after 5 seconds the relay should be turned off as well. So could anyone help me out with a suitable circuit diagram for my application??
sokoloff:
Try something like this:
http://tinyurl.com/ycfydrey

(If that short link breaks, here's the long link.)
Zero999:

--- Quote from: sokoloff on July 25, 2018, 10:22:53 am ---Try something like this:
http://tinyurl.com/ycfydrey

(If that short link breaks, here's the long link.)

--- End quote ---
I know it's just a simulation, but the 555 will not be able to supply the current of that lamp.

Here's how it's done in LTSpice. A diode is added across the resistor, to discharge the capacitor, when the power is disconnected.

Adhith:

--- Quote from: Hero999 on July 25, 2018, 01:59:15 pm ---Here's how it's done in LTSpice. A diode is added across the resistor, to discharge the capacitor, when the power is disconnected.



--- End quote ---
Thank you very much Sir for your reply. I have some doubts regarding the circuit and could you help me out??
1)This timer is used to disconnect another circuit board for the first 5 seconds. the power supply for the timer is taken parallel from the other circuit board and there is no separate switch for the timer. what i want is that after the 5 seconds the timer circuit should be turned off through out the use of the other circuit until the switch for the other circuit is again restarted. Does this circuit provides this function??

2) on reading the datasheet its found that the max working voltage for the 555 is 16v and however my supply voltage is around 16.8(4s Li ion cell). So a linear regulator 7812 would be needed at the input right??

3) on the right hand side W1 and load 10R represents the switching side of the my relay right ??
Zero999:

--- Quote from: Adhith on July 25, 2018, 03:07:56 pm ---
--- Quote from: Hero999 on July 25, 2018, 01:59:15 pm ---Here's how it's done in LTSpice. A diode is added across the resistor, to discharge the capacitor, when the power is disconnected.



--- End quote ---
Thank you very much Sir for your reply. I have some doubts regarding the circuit and could you help me out??
1)This timer is used to disconnect another circuit board for the first 5 seconds. the power supply for the timer is taken parallel from the other circuit board and there is no separate switch for the timer. what i want is that after the 5 seconds the timer circuit should be turned off through out the use of the other circuit until the switch for the other circuit is again restarted. Does this circuit provides this function??

2) on reading the datasheet its found that the max working voltage for the 555 is 16v and however my supply voltage is around 16.8(4s Li ion cell). So a linear regulator 7812 would be needed at the input right??

3) on the right hand side W1 and load 10R represents the switching side of the my relay right ??

--- End quote ---

* Your description is unclear. Do you want delayed on, or delayed off? As drawn the circuit will turn the relay on for the first 5 seconds, after power is applied, then turn it off. If you want the relay to be off, when power is first applied, then turn off after 5 seconds, then the relay coil and D2 should be connected between the 555's output and +V.
* Yes, that will work, but you might want to use the LM7808, to give more headroom, although the 555 will still work even if the  LMM7812 stops regulating, so it won't be a problem. Another solution is to use the ICM7555, which will work up to 18V but it can't source as much current, as the  classic NE555. It depends on the relay.
* Yes, the relay is modelled, for the purposes of the simulation, as a current controlled switch, with the input being the current through a 10H inductor, with a series resistance of 500R.
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