Mosquito Repeller

For this project, I made a Mosquito repeller using the Future kit FK918. The circuit uses a piezo board to generate frequencies in the range of 15kHz-38kHz, which interferes with the mosquitoes' receptors, making them uncomfortable when they fly over the circuit. The circuit utilises a 3VDC to power the piezo into creating sound waves at a frequency that is audible to humans but irritating to mosquitoes.

In addition to being annoying, mosquitoes can spread desease. Repellents are a widely used solution, but long-term use can make them expensive or dangerous. The FK918 Mosquito Repeller uses ultrasonic sound waves to repel mosquitoes, making it an inexpensive and environmentally friendly solution. For anyone interested in practical electronics with uses in everyday life and public health, this project is perfect for you.

FK918 (Website)

Materials in Future kit set:

PCB (1x)

Piezo board (1x)

Transistors (4x)

10uF Electrolytic capacitor (1x)

3uF Electrolytic capacitor (2x)

Ceramic capacitors (2x)

Zener diode (1x)

Solder

Wires

Trimmer potentiometer (1x)

Resistors:

1. 100Ω
2. 330Ω
3. 3.9kΩ
4. 12kΩ

Materials not in future kit

6A 125V AC switch (optional but recommended)

Battery holder

1.5V batteries (2x)

I have already given the values of each resistor and the names of the parts, but it is important to double-check everything just in case your set has different parts. Labelling the parts also helps you stay organised, so you don't lose your parts or use the wrong parts.

1. Use any blank paper and lay out all the separate parts
2. Double-check the values of your resistors and make sure there are 2 of each
3. Double-check if you have two 3uF electrolytic capacitors and one 10uF one
4. All the ceramic capacitors and transistors are the same, so it doesn't matter which order you put them in, all that matters is the polarity (electrolytic capacitor)

1. Make sure to work in a well-ventilated area as smoke can cause irritation
2. Use the soldering iron carefully, the tip can reach up to 450℃, so always hold the handle
3. Wear safety goggles at all times while soldering
4. Make sure your workspace is clear
5. Wash your hands after soldering or wear gloves while soldering
6. Use a damp sponge if you need

Credits: Future kit website (PDF for steps)

Quick basics of soldering:

Place the part into the PCB holes, then bend the leg and hold it in place (use clips if you need). Heat the copper part, then feed in a little solder and let it cool into a shiny cone shape.

1. When soldering, start from the lowest, then go to the highest
2. Start off with the resistors, solder one pair at a time. Remember to insert it into the slot where it is supposed to go, and make sure not to put anything in the wrong slots or else the kit won't work. Once you insert the resistor, bend the legs so it is easier to solder (see image)
3. Solder the zener diode
4. Solder the electrolytic capacitors. Make sure to check the polarity:

There are two 3uF capasitors and one 10uF capasitors, the circuit will tell you where to put everything but make sure the longer leg goes into the hole which says "+"

1. Solder the ceramic capacitors
2. Solder the transistors
3. Solder the potentiometer

Note: Make sure that the solder bits don't touch each other

Piezo

1. Cut two equal-length pieces of wire, then strip some of the rubber off on all sides so that the copper is exposed
2. Put the copper part through the middle two holes that have "PZ" in between them (see image) and bend it so it touches the copper part of the PCB
3. Solder the two wires onto the PCB

This part may be a bit challenging, so it is better to use clips to hold everything in place.

1. Solder one end of the wire to the golden bit of the piezo board and solder the other end to the white bit (colours may be different, so just solder one bit to the outside area and the other to the middle). Make sure the solder doesn't touch both sections at once

Battery and switch

1. Cut a red wire (colour doesn't matter, just helps with organisation), clip it, then solder one end to any part of the switch
2. Put the red wire through the hole that says "+3V" and solder it in place
3. Next, solder the battery pack's black wire into the hole that says "G"

Don't have a switch? No problem

What to do if you don't have a switch

If you don't have a switch, it is easier to finish the circuit. All you need to do is:

1. Follow all the steps under the Piezo section
2. Solder the battery pack's red wire into the hole that says "+3V"
3. Solder the battery pack's black wire into the hole that says "G"

Now that you are done, here is what the circuit should look/sound like:

No sound from the buzzer: Check the polarity of everything and make sure all parts are soldered firmly. Also, verify the battery voltage (3V).

Weak or distorted sound: Cold solder joints can reduce performance. Reheat the joint and apply fresh solder until shiny.

Circuit not turning on: Confirm all components are put in the correct spots. You can double-check where to put parts using the schematic. Also make sure no solder bits touch each other

Overheating components: This usually means a short circuit. Make sure no bits of solder touch each other, if they do, then remove them with a solder wick or desoldering pump.