Need help on generating variable pulse to control a relay

Thread Starter


Joined Oct 3, 2010
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.



Joined Jun 22, 2012
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