Float sensor read and timed trigger

Discussion in 'The Projects Forum' started by RoboDOS, Jan 29, 2015.

  1. RoboDOS

    Thread Starter New Member

    Jan 29, 2015
    I've got a pump station attached to a NO float sensor (reed switch), when the float lowers the circuit closes, the pump activates. All easy

    Now, I need a way to daily also force the pump station to run for say 10 minutes at a specified time regardless of the float state.

    My idea is to put a small controller (Raspberry Pi) in line... Attach the reed switch that was attached to the pump station (P) to an input DIO (1) and then the pump (P) to a different DIO (2) set as an output. When the float circuit closes I'll activate the output (2), but also activate the output at the specified daily expected time.

    When I set the output it's providing 3.3V. My concern is that the pump station is also sending some current down the line and looking for the circuit to close. So if I connect the output (2) of my controller to the input of the pump station, I'm not sure if that could damage the circuit of either the pump station or the controller... Or if it will work...


    I had considered using a SPDT relay instead.. Using the + side of the pump station input as the source and connecting the sensor to the NC terminal of the relay... Then when I want to close the circuit at an appointed time I switch the relay which attaches the NO side to the - side of the input... So when I throw the relay the pump station sees this as a closed circuit. I think this would work but I'd prefer for my controller to know when the float is triggered. (And I'm sure a transistor maybe better here than a relay)
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    For complete isolation of the existing reed contact and the timed controller you are planning, I would use a secondary relay, operated by the timed controller.
    You say that the existing controller sends a 'current' thru the reed contacts, as you have not specified the 'current' thru the contacts or the 'voltage' across the contacts when open, a secondary relay would be my choice.

    A Raspberry Pi sounds a bit of an overkill for this application.
  3. sirch2

    Well-Known Member

    Jan 21, 2013
    Is the pump a submersible type? If so they generally rely on being in water for cooling, the pump may well have a thermal cut-out but you may want to consider what would happen if the pump was running when the sump is dry.