3sec delay and then Non-stop output.

[Magok]

Hello there,
I'm searching couple of days now for a circuit that will do the following,
when it gets input voltage (logical 1) after a 3 seconds delay will give output voltage.

From the search i found that LM555 could give you a period of output but I have no idea how set different delay timmer and output durration....

Any suggestions are welcome,
Thanks in advance

 

[ericgibbs]

hi,
Whats the 'input voltage'.? ,also what is the 555 output controlling.

 

[Magok]

input voltage is 7V, what do u mean output controlling?

 

[ericgibbs]

input voltage is 7V, what do u mean output controlling?

hi.
The output of the timer [555] must be doing something.? eg: driving an LED or transistor etc.

 

[alec_t]

Here's guidance on using a 555:-
https://www.electro-tech-online.com/threads/multichannel-rf-transmitter-and-receiver.445/

 

[Magok]

it will be connecting to a led....

 

[WTP Pepper]

View attachment 64468Use a resistor to charge a capacitor and pass the output of the cap through a Schmitt Trigger. A3 can be any CMOS logic device i.e AND gate.
Time delay before output goes high =0.7 * R * C (can supply the maths if required). The output will fall to zero almost immediately once the input drops to zero (ish).
Using CMOS, this will operate to 18V.
Choose a low leakage cap like a tant cap.
c=10uF & r=470K will get you close enough.

 

[Magok]

woaah thanks a lot for taht I think I got an idea know how to make it work, I'll try to get this done now

 

[colin55]

Just use a transistor and delay circuit.
View attachment 64473

 

[WTP Pepper]

Just use a transistor and delay circuit.
View attachment 64473

Where is the input trigger? If just connecting the battery then the problem is if the you remove the battery and connect quickly again, the LED will light almost immediately due to charge left on the cap. A reverse diode across the resistor may help if there is sufficient load left on the supply which looks there isn't.

My suggestion would need the input to be driven low to 'reset' and not left to float. A 1K resistor across the input would do it pretty quickly should the input be left to float..

 

[harold777]

I think the schmitt circuit ( Post #7) is preferable - and it's acceptable to parallel gates to achieve a marginal improvement in the o/p current (typically 20mA per gate - read Data-Sheet). Most 4000-series are several gates inone package. Indeed inputs should be defined even if the gate isn't used, to prevent oscillation troubles - Schmitts tend not to suffer from this, but "good practice..."
The circuit presumes the input source swings between zero and 7v
I would add that a buffer cct might be a good idea aas we don't know what this i/p is and it might be disconnected. A simple buffer transitor should avoid gate damage due to stray spikes.
Also, to be picky, there should be a resistor 1-10k between the capacitor and the gate i/p, so protection diode current is not excessive.