Introduction: LED Water Beacon

About: We design simple electronics circuits.

This Instructable shows you how to make a simple LED water beacon. The blinking LED will turn on if put the sensor in water.


parts: LED, bright LED, colour changing LED or blinking LED, contact sensor, 9 V battery harness, 9 V battery, 1 kohm resistor, old food container, masking tape.

tools: wire stripper, scissors.

optional tools: soldering iron.

Step 1: Build the Circuit

The 1 kohm resistor limits the current across the LED.

Maximum current will equal to:

(Vs - Vled) / Rd = (9 V - 2 V) / 1000 ohms = 7 mA.

Most LEDs supposed to be biased at currents of 10 mA.

Thus you can use a smaller resistor.

Step 2: Testing

I placed the circuit inside the ice cream container to shield it from water.

The video in this step shows the container out of the water and the two sensor contacts connected together.

You can click on this link for a more complicated water sensor that can driver higher current loads: