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Can i control the time wich a relay turns on without using a programable ic? Answered

Hello guys im building a project but i have an issue i need it to keep the current flowing for 5 secs to turn the relay for 5 secs i mean i press n release the button and the relay keeps on for 5 secs i dont have acces to pics and yet i do have arduinos but im not gonna spend an arduino for a project that means only 1/4 of my grade... thanks



Best Answer 8 years ago

Use a transitor to control your relay place a 1k_4.7k resistor inseries with the base and use an electrolytic cap to release it's charge into the base via the series resistor. this will hold the base ON for a period depending on the value of the cap and keep the relay energised. Experiment to achieve the ideal timing point. Nice and simple, place a diode across the relay coil anode to transistors collector, cathode to positive supply side of relay coil.

thanks every one ;D hes answare seems to b a pretty eassier for me but thanks for the other answares :D

You need a 555 timer in monostable mode. <a href="http://www.doctronics.co.uk/555.htm#monostable">THIS</a> is a circuit which will give you exactly what you need, and it also has the formulas to calculate the time delay.<br />

Sounds like a classic application for a 555 timer chip...

I agree. Long accurate delays can be a bit of a problem for the 555 though.

There are two instructables on how to use the timer from a microwave.

 I would just play with capacitors until you find the correct value to hold the relay for the wanted amount of time.  Just place it in parallel with the power that holds the relay the open.