Hello Everyone,
I am new to the forums and very much a novice when it comes to electronics. I am trying to build a simple circuit that will control a topoff pump for my fish tank. Currently I have the pump wired up to an electric relay which is attached to a float switch in the tank. The float switch is very sensitive to the water level which means the pump is going through very frequent start/stop cycles. The pump is typically on for about 10 seconds every 5 - 10 minutes. What I would like to do is have the float switch trigger a timing circuit that will keep the pump running for about 5 minutes at which point it will shut off and wait for the next trigger (i.e. the float valve lowering with the water level). I have been reviewing this page http://www.kpsec.freeuk.com/555timer.htm and it looks as though I need to build the circuit to the right of the heading "555/556 Monostable". What I am having trouble with is how to determine the capacitor and resistor values to achieve a time period of 5 minutes. Based on the formula T=1.1 X R1 X C1 I worked out that for a T = 300 Seconds I could use a 1000 uF Capacitor and a 270 Ohm resistor. Is this correct and is it really this easy?
I am new to the forums and very much a novice when it comes to electronics. I am trying to build a simple circuit that will control a topoff pump for my fish tank. Currently I have the pump wired up to an electric relay which is attached to a float switch in the tank. The float switch is very sensitive to the water level which means the pump is going through very frequent start/stop cycles. The pump is typically on for about 10 seconds every 5 - 10 minutes. What I would like to do is have the float switch trigger a timing circuit that will keep the pump running for about 5 minutes at which point it will shut off and wait for the next trigger (i.e. the float valve lowering with the water level). I have been reviewing this page http://www.kpsec.freeuk.com/555timer.htm and it looks as though I need to build the circuit to the right of the heading "555/556 Monostable". What I am having trouble with is how to determine the capacitor and resistor values to achieve a time period of 5 minutes. Based on the formula T=1.1 X R1 X C1 I worked out that for a T = 300 Seconds I could use a 1000 uF Capacitor and a 270 Ohm resistor. Is this correct and is it really this easy?