Sump pump alarm Mark II

I finished the second version of the sump pump alarm. This revision has the following changes:

  • Sump pump alarm 2 3.9 V Zener (D1) instead of 5.1 V. This gives ~5.1 V to the PIC with a fresh battery. The PIC is rated down to about 3 V at the 4 MHz clock frequency used, so this keeps it running at least until the battery drops to 6.9 V, instead of cutting out at around 8.1 V. Depending on the discharge curve of a particular battery in this application, that could add some extra alarm time.

  • Innards More solid construction. The line cord passes through a hole in the enclosure rather than a notch, which makes it less likely to pry the (bottom) lid off during handling. Also, the buzzer and relay are bolted to the bottom, and the battery is loosely tied to the relay as shown here. So, it should be more stable during transport and handling.

  • I decided not to drill holes to transmit the sound. This will be going in the basement of our rental house, which is right under the living room, and the buzzer is, if anything, louder than the previous one, so I think it’ll be audible - and it’s generally not an emergency situation that should wake someone up at that house. Keeping the enclosure more tightly sealed might help improve component longevity.

The whole project took about 4 hours this time; not bad for something not designed for mass production.