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How to Ruggedize Electronic Sensors for Long Life – Waterproofing a Capacitive Analog Soil Moisture Sensor

How to ruggedize a capacitive analog soil moisture sensor – Ruggedizing and waterproofing the analog soil moisture sensor is necessary to ensure long life operation of the moisture sensor within real world applications.  Without ruggedizing and waterproofing, a soil moisture sensor is all but guaranteed to short out when (not if) it gets wet. A rugged and waterproof soil moisture sensor increases system reliability while also lowering the total cost of ownership and reducing overall maintenance of your IoT and/or gardening systems.

Video: How to Ruggedize and Waterproof an Analog Soil Moisture Sensor for Long Life Operation

Materials Needed:

  1. Capacitive Analog Soil Moisture Sensor with Connector
  2. CRC Urethane Seal Coat Viscous Liquid Coating Aerosol Spray
  3. 3:1 Dual Walled Glue Adhesive Lined Heat Shrink
  4. Scissors, paper and a heat gun

Steps to Ruggedize Moisture Sensor:

Prepare the Soil Moisture Sensor: The first step is to clean the moisture sensor with isopropyl alcohol. Next connect the analog PCB connector to the sensor. We will apply a clear urethane seal coat to protect and ultimately waterproof the components on the soil moisture sensor board. After snapping the board connector in place, place the sensor with components facing upward on top a piece of paper or cardboard. Next position a second piece of paper over the moisture sensor board covering the entire bottom of the board but leaving the board components exposed.

Coat the Soil Moisture Sensor PCB with Urethane Seal: Next, in a well-ventilated area, generously spray the first coat of clear urethane sealant over the soil moisture sensor components. Let the sensor dry for at least 30 minutes. Apply a second coat after the urethane seal dries to increase protection and let sit again for at least another 30 minutes. Next turn the sensor board over. Finally apply two separate coats of urethane sealant to the backside of the moisture sensor.

Apply a 3:1 Double Wall Adhesive-Lined Heat Shrink: Now place a strip of double walled adhesive lined heat shrink over the sensor components previously protected with a double coat of urethane sealant. Take a heat gun to heat up the heat shrink. Be sure to apply enough heat to melt the glue adhesive lining the heat shrink. This will ensure further waterproofing for your newly ruggedized soil moisture sensor. While still hot, firmly press the heat shrink together to seal the opening near the connector wires as shown in the video above.

Now you have ruggedized and waterproofed your analog soil moisture sensor.

You can also purchase this ruggedized and waterproof analog soil moisture sensor here in the Adosia IoT Store.

4 thoughts on “How to Ruggedize Electronic Sensors for Long Life – Waterproofing a Capacitive Analog Soil Moisture Sensor

  1. do you not need to seal the “blade” itself, as in this instructable (https://www.instructables.com/id/Waterproofing-a-Capacitance-Soil-Moisture-Sensor)? see step 10: “Apply a Thin Layer of Nail Polish at the Sensor / Tubing Seam”. the author was able to leave the entire sensor, including the electronics) underwater for several days.

    1. You certainly can seal the edges of the PCB – from our experience though it’s not necessary when using some of the higher quality sensors as they will typically last the season regardless. As sealing the edges can limit saturation effects on the board over long periods of time, we’re looking at adding it to our process. I would recommend sealing the edges particularly where calibration cannot regularly occur as regularly as desired.

      Also, from our experience, you can also seal the entire blade – this will result in a smaller analog range such as 550-750 (instead of something normal which would operate closer to the range of 200-750).

      1. how about “masking” the blade with, say, cardboard pieces that come almost to the edge and then spraying to seal the edge, such as below. “X” is a cardboard mask, one on both sides. Then spray on the edges, all around.

        |———-|————–\
        | electr |xxxxxxxxx \
        | onics |xxxxxxxxx /
        |———-|————–/

        this should provide additional protection without lowering the sensor range. what do you think?

        1. It might work but the urethane coating bleeds fairly easily – so offhand I think such a scenario would make the process susceptible to getting unwanted urethane seal on the blade – though this shouldn’t impact the analog detection range.

          We’ve used clear nail polish before in some trials and found that using a fine brush to apply the urethane sealant coating helps a great deal – with this in mind it may make sense to spray some urethane seal coating into a cap/cup and use a fine brush to apply the sealant to the blade edges, while using alcohol to clean any traces from the blade itself before the urethane dries.

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