My plan is to build a circuit to generate a variable pulse to control a relay, which in turn controls the on/off switching of a 24 V solenoid valve. I would like for it to be able to have 5 different pulse rate. For example;

1 second on, 1 second off
1 second on, 2 second off.
1 second on, 3 second off.
1 second on, 4 second off.
1 second on, 5 second off.

I already built a circuit based on the attached image without the 0.01 uF capacitor and test it using an LED. It works fine on an LED but when I used a 6V DC relay, the pulse is somewhat different and gets faster over time then stops working after a while until I switched it off and on again. Why does this happen? Can someone give an explanation to why the relay behave like such and how I can fix it? Also, how do I achieve for a 5 variable pulse rate like I mentioned above? Do I have to change the capacitor values? If so then how can I figure out what value of capacitor for a specific pulse rate? Is there a formula to obtain the values? Any help will be greatly appreciated.

Thanks in advance.

 

Check this out, you can enter the values yourself , i suggest 420K for Ra, and 150K for Rb, 10uF for Ct as a starting point for 1second/ 5 seconds, then alter Ra..Rb as necessary

http://www.delabs-circuits.com/cirdir/theory/gates/doc00019.html

for driving a relay put a diode across the relay coil reversed biased like this , http://www.google.co.uk/imgres?q=ba...=187&start=0&ndsp=24&ved=1t:429,r:5,s:0,i:100

 

Thanks, that helps a lot.