Solid State Optical Sump Pump Controller
Introduction: Solid State Optical Sump Pump Controller
Recently I found out my dad had an inconvenient situation with the sump pump in his basement. The sump pump sits at the bottom of a four foot deep well and is activated by a small float that moves up and down. The float is connected to a mechanical switch on the pump housing.
During the wet season, the pump turns on and off about once a minute and the switch contact lasts only about a year before succumbing to mechanical failure. When it does, my dad has to undo the outlet hose, hoist the pump out of the well and replace it with a spare pump he keeps around for the task. Then, he replaces the switch contactor on the broken pump so he can have it ready for next year. This costs about $40 a year, not to mention the labor involved in swapping out the pumps and replacing the contactor each time.
To solve the problem, I set out to design a solid state optical sump pump controller that has no moving parts to wear down. My idea was to bypass the mechanical float on the pump itself and to instead make a new float that would mount to the side of the well. This would consist of a plastic bottle and a dowel rod. The dowel rod would move up and down and trigger two optical sensors mounted on the side of the well. I would then build a circuit to turn the pump on and off using a solid state relay. 742
Because this would be contactless and have no electromechanical parts, it would never fail due to wear.
Supplies
Float Assembly:
* One plastic bottle
* One dowel rod
Optical Float Level Sensor:
* Two Photointerrupters
* Hookup wire
Option 1: TTL Based Control Logic:
* Two 2.2kΩ resistors
* One 100Ω resistor
* One 7400 quad-NAND gate integrated circuit
* One 180Ω resistor (optional)
* One indicator LED (optional)
* One protoboard PCB
Option 2: Arduino Based Control Logic
* One 100Ω resistor
* One Arduino Uno (an ATTiny based board could work as well)
Power Supply:
* One 5V USB charger
* One USB cable
Pump Relay Assembly:
* One solid state relay
* One AC plug
* One AC outlet
Step 1: Making the Optical Water Level Sensor
The water level sensor consists of a shaft with a central hole slightly larger than the dowel rod. When mounted to the side of the well using the attachment bracket, it allows the float and dowel rod to slide freely up and down along with the water level in the well.
At two points along this shaft are positioned photointerrupters. These devices consist of a infrared light source and a light detector. When the dowel rod slides into the groove in the photointerrupter, it interrupts the light beam, turning off the current through the light detector. The photointerrupter sit well above the water level and are not intended to get wet.
I chose to make the water level sensor shaft out of 3D printed segments so that I could easily adjust the length by adding segments as needed. Each segment has a central cutout for inserting a photointerrupter, but only two of the segments will have one.
I also made a bracket for attaching the sensor to the side of the well.
Autodesk Fusion 360 Design
Step 2: Wiring and Operation of the Water Level Sensor
Along the sensor bar, there will be photointerrupters that will be blocked by the dowel rod when the water reaches the low and high point. One side of each photointerrupter contains an LED light source. Both of these will be wired from 5V, in series with a current limiting resistor (shown in the schematic), down through a common ground.
The side of the photointerrupter with a dot contains a light sensitive transistor. The signal lines go to the leads nearest the dot, while the opposite leads are wired to a common ground.
The control logic will pull the two signal lines up to 5V while the phototransistor is in shadow, but if light falls on the transistor, it will conduct and bring the signal line to 0V; therefore, when the dowel rod is present, the signal line will read 5V, while when it is absent, it will read 0V.
I used an ITR9608-F photointerrupter because it has a 5mm gap, which is just wide enough to let my dowel rod through.
Step 3: Making a Float With an Adjustable Rod
For the float, I used a small plastic bottle and the dowel rod. I wanted the length of the rod to be adjustable, so I drilled a hole on the bottle cap to allow me to insert the rod partially into the bottle. 267