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Latching Relay Board for Moisture Sensors


  • Wide AC input voltage range.
  • Samples the sensor and updates the relay approximately every 10 minutes.
  • Has a special real time configuration mode, where LEDs are active and the sensor and variable resistor are read continuously.
  • Can be configured as a normally open or normally closed contact with a simple jumper setting.
  • Uses a low power solid state relay.
  • Can control a 10A load up to 240VAC.
  • Interfaces to a single VH400 probe.
  • Low power.
  • LED indicators, indicate power on and relay contact.
  • Terminal blocks for quick connection.
  • Low price.
  • Small size.
  • 4 mounting holes in each corner.


  • Crop Steering.
  • Rain Sensor Replacement
  • Interruption and control off irrigation and sprinkler systems.
  • Battery operated valves and control systems.
  • Perfect for evaluating our VH400 soil moisture probes.
  • Interruption and control off irrigation and sprinkler systems.
  • Interface soil moisture sensors to home automation systems.
  • Control and monitoring of moisture content in bulk foods.
  • Rain and weather control functions.
  • Environmental control functions.
  • Water conservation applications.
  • Fluid level measurements and control.

Battery Powered Latching Relay Board Details

W hit the battery powered Latching Relay board you can control anything with any Vegetronix sensor. You can control sprinkler valves, pumps, lights; anything. It receives input from any Vegetronix sensor, or third-party sensors that have a 0-3V voltage output.

Can Be Powered by Battery

Drawing only 65uA during normal operation, this board is perfect for applications where battery life is critical. It interfaces directly to Vegetronix soil moisture sensors, and has a variable resistor which set's the relay trigger point. Because it uses a low power latching relay, it only requires a brief pulse of current to update the state of the relay. The soil moisture sensor is sampled every 10 minutes to update the state of the relay.

Easy to Use

It has 2 LEDs to indicate that the board has power, and the on/off state of the relay. For low power mode the LEDs can be disabled with a simple jumper switch. It can be wired in series to valves including latching valves and block watering events from a valve clock.

The VG-RELAY-LATCH board interfaces to a single VH400 soil sensor, and can activate a low power AC load such as a valve or alarm, or other control device, when a moisture level is reached. The threshold is easily set with the onboard variable resistor, and a small screwdriver. The relay board can be configured with a jumper to turn the relay on when the sensor detects wetness or on when the sensor detects dryness.

This board has a special configuration mode, which can be entered by setting a jumper. In configuration mode, the LEDs are active, and the sensor and variable resistor are continuously updated. This mode consumes more power, so it should not normally be used beyond initial calibration.

Can be Used With Irrigation Timers to Save Water and Money

This relay board can be used as an input to many sprinkler timer controllers, simulating a rain sensor, but giving more accurate feedback to the controller. For more detailed information on how this works see the article "How to Replace a Rain Sensor with a Soil Moisture Sensor"

If your irrigation timer doesn't have an irrigation timer, no problem, you can still use this board to interface with your sprinkler timer, to save water. For more detailed information on how this works see the article "How to Control Multiple Sprinklers with a Single Moisture Sensor"

Evaluate Vegetronix Sensors

The VG-RELAY-LATCH also serves as an evaluation board. If you are thinking about testing our VH400 soil moisture sensors you should consider purchasing this board as well.

Vegetronix Modular Building Blocks

We take a modular approach with our product lines. Each product is simple and low cost, and will easily interface to all of our other products. This approach allows you to build any type of application from our basic set of components.

We Want you to be Happy

Ordering is easy and low risk. Since we build our own products at our factory, all of our products are in stock. When you place your order from our website, it will ship same day from our factory, and you'll have it in your hands in just a couple of days. We ship to nearly EVERY COUNTRY in the world.

If you aren't amazed and delighted by your new Relay Board, return it for a refund within 30 days.

Calibration Procedure

  1. There is a jumper on the board, namely J2. (It's a black 2 pin header.) Make sure it is shorted with the black plastic jumper. When it arrives this should have already been shorted with the jumper.
  2. Insert the sensor into terminal block TB2. Red wire to +5, Black to Sense, and Bare wire to GND.
  3. Power the board with 9VDC, or 9V battery to terminal block TB1.
  4. If the jumper is on correctly, the power light should come on. The LED D4, says "POWER ON" underneath it. If the power light doesn't come on and the jumper J2 is in place then you've probably hooked up the power incorrectly.
  5. The relay LED will now also be operational with the jumper in place, but with there is a nuance to it. The potentiometer is only read about ever second - it is not continuous. So you must adjust it very slowly, and incrementally. If you turn it to fast, it wont be read and you will overshoot.
  6. Adjust the pot until you have it at the correct level. The LED light will either turn on when it passes the threshold set by the pot, or off when it has not.
  7. The polarity jumper J3 can be used to reverse the polarity of the relay, from normally closed to normally on. This can also be used to verify that the relay light is working. If the relay light is off, it should turn on with one of the cases: of the jumper being inserted, or removed.
  8. Once the board is calibrated, remove the jumper from J2, so that the LEDs do not waste power. (You can put it on just one of the pins, so that you save it for future use.)

Relay Board Selector Guide

Vegetronix offers a variety of relay boards for nearly every application. See our Relay Board Selector Guide for help in determining which board is appropriate for your application

Other Vegetronix Products of Interest

Pricing and Ordering Info

We ship to nearly EVERY COUNTRY on the planet, directly to you from our factory.

99% of orders ship same day.

Part Number Description Price Purchase
VG-RELAY-LATCH Latching relay board for the VH400 probes. Interfaces to a single VH400 Moisture Sensor Probe. Buy Now
BH-AA-9V 9V battery holder with snap clip. Holds 6 AA batteries. Recommended for all VegeHubs. Buy Now
BATTERY-BOX-6AA Rain Resistant Battery Box for 9V battery holders. (Does not include the battery holder. Also purchase the BH-AA-9V from the link directly above.) Buy Now

For volume pricing contact us.


Power consumption 65uA
Supply Voltage 6V to 24 VDC
Relay Load 10A 250VAC
Dimensions 2.0"x1.75" (5.08cm x 4.445)
Number of sensor interfaces 1
Number of relay outputs 1

Wiring Table

Pin Description
2 6 to 24VDC
Pin Description
1 GROUND: (connect to probe ground - bare wire)
2 SENSE: (connect to probe output - black wire)
3 POWER: 5V (connect to probe power - red wire)
Terminal Block TB3 (RELAY INTERFACE)
Pin Description
1 Relay contact 1
2 Relay contact 2

Additional Information

How to Get Started

The best way to get started is to order a few low cost probes and relay boards and try them out in your application.

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