Float Switch ensure activation please help...

Thread Starter


Joined Jun 29, 2011
Hi all,

I have a tank containing water and within this tank there is a large bilge pump that mixes the tank on activation..

I have a float switch the same as this one of which activates or deactivates another smaller pump


What is happening is when I turn on the big mixing bilge pump depndant on the tanks water level it is swirling the water around and triggering the float switch i.e knocking it up and down...what I need is a way of the float switch only to trigger when its been closed for a set time period i.e 30 seconds this way I can be sure when it triggers the smaller seperate pump it is doing so based on the water level in the tank rather than if the mixing pump is knocking the switch up and down.

Any ideas welcomed I am sure there is some kind of relay etc that only activates after a set time of being closed.



Joined Nov 30, 2010
Yes, you can do it electronically, but I agree with mcgyvr. Much better to use a large tube with small holes to average the amount of water.


Joined Feb 1, 2010
I know this is probably over-kill for you but I had a similar problem with a bilge pump. I used a microcontroller (a PIC but an Arduino or PICAXE would be the easiest to get started with) and got the liquid level switch state via a pin configured for digital input and then switched on the pump via a simple motor controller circuit using an output pin, N-MOSFET, resistor and diode. That allowed me to add whatever kind of hysteresis I wanted so that once started the pump would run for at least n-seconds, etc. Of course, there are simpler ways to do this with 555 timers and discreet components. However, once you have the microcontroller smarts in your system there's always more 'features' you can add easily.

If you're interested all the schematics can be found here (http://backyardsolar.blogspot.com - just look about 10 posts back). You can ignore all the solar power parts.

Thread Starter


Joined Jun 29, 2011
I think this is the answer...

IS-ARM on the products page (advanced relay module)

As I see it it will activate the pump after a set amount of time but if you interupt it i.e bouncing up and down during this time it will cancel the timer

works a treat :)