Introduction: Venus Fly Trap

Picture of Venus Fly Trap

This cool little device was designed to behave like a real Venus Fly Trap. This very unique project is a lot of fun to make and play around with and it actually works!! Check out the video clip and see how it operates.

Step 1: Assemble the Components

Picture of Assemble the Components

The project requires an intermediate level of electronic construction and craft skills to assemble. Start by reviewing the project steps and collecting the components and planning each step carefully before proceeding.

There are four main items to be built in the project

- Case and Solenoid

- Trap Door

- Trap Door Frame

- Circuit

Step 2: Build the Trap Door

Picture of Build the Trap Door

The trap door is made in three parts. The door, chamber curve and the solenoid bracket.

1. The Door

The door can be built by using these dimensions and carefully cutting a single piece of 2.5mm thick Styrene sheet 109mm long and 82mm wide. Mark a line 55mm in from the 82mm edge as this will be the crease line you will use to bend the styrene to a 55 degree angle. Styrene can be bent easily when it is gently heated over a gas flame and bent over a wooden straight edge.

Note: Adult assistance is required for this step. Ensure adequate safety measures and gloves are used during this process. The gas flame should never directly touch the styrene as it could burn, ignite or discolour. This must be done outdoors with adequate ventilation and a fire safe environment.

In order to get a good clean bend I recommend making up a thick wooden block template which can be cut to the correct angle. This way, when the styrene is heated until malleable, it can be quickly draped over the wood and pressed into shape with another block of wood.

Once the correct angle is achieved cut a solid metal rod of (2mm diameter) long enough to overhang each side of the Trap Door by 7mm. Glue the rod into the crease of the Trap Door with a strong two part epoxy glue.

2. The Chamber Curve

The Chamber Curve is made from very thin Styrene (0.5mm) which is bent around two supporting styrene struts as seen in the photos. Styrene glue (Model Plastic Glue) is used to hold the Chamber Curve, Struts and Door in place.

Note: When using Styrene glue ensure you work in a ventilated area and follow the safety instructions.

3. The Solenoid Bracket

The picture and diagram shows a special aluminium bracket has been made and attached to the centre of the underside of the Trap Door. This is used to attach the Solenoid coupling rod that you will build later.

The picture also shows another adjustable aluminium tag that can be added later if the door does not stop in the correct position flush with the surface of the plastic case.

Step 3: Install the Trap Door

Picture of Install the Trap Door

Position the Trap Door at the front of the plastic case with the rod forming a hinge on either side of the top of the case.

Mark around the Trap Door so a hole can be cut out of the case big enough so that the door fits snuggly however with enough clearance so it can swing open freely without interfering with the sides of the plastic case or the edges of the hole.

Use a craft knife and a steel ruler to score around the markings several times until the hole is cut through the top of the case.

Cut two small aluminium strips and attach these using a nut/bolt/screw to hold the metal rod straight.

This step has been completed successfully when the trap door can swing freely through the hole in the plastic case.

This may require some trial and error with carefully trimming the door and the case which will require some perseverance.

Step 4: Install the Infrared Sensors

Picture of Install the Infrared Sensors

The Infrared LED needs to be positioned on one side of the Trap Door and the four Sensors on the other side as in the picture.

This ensures that any object or insect that interrupts the LED Infrared beam hitting any of the four sensors will trigger the Trap Door.

Mark the position of the LED and Sensors and drill small holes through the top of the case just big enough for the LED/Sensor legs to fit snuggly in position.

Use Vero board on the underside of the Plastic Case and solder ribbon wire to the LED/Sensors ensuring it is long enough to reach the far end of the Plastic Box.

The Infrared sensors need to be covered from natural light to avoid interference so a simple styrene housing can be built around the sensors.

Be careful to ensure there is clear line of sight between each sensor and the Infrared LED.

Step 5: Install the Solenoid

Picture of Install the Solenoid

The solenoid is used to pull the trap door closed and needs to be positioned in the case so that when it closes it can do so without being obstructed by wires or mounting brackets/screws.

It should be mounted in a bracket and fastened to the centre of the plastic underside of the case ensuring the plunger is held in place by the bracket - see pictures.

Build a universal coupling from an aileron kit that you can purchase from most model airplane shops. This needs to be adjustable so use a threaded bar between the plunger and the aileron clip so that the length can be adjusted later.

Step 6: Trap Door Chamber Frame

Picture of Trap Door Chamber Frame

The Trap Door Chamber Frame is constructed to enable the Trap Door to return to the closed position and sit flush with the top of the plastic box. It also creates a chamber where the insect is trapped once the trap is reset. The chamber can be accessed from the front of the unit through the Chamber Door.

1. Trap Door Chamber Frame

The Trap Door Chamber Frame is built to be inserted and removed for ease of assembly and adjustment. The frame is made from styrene that has an end stop that the Trap Door hits when flush with the plastic box.

A picture of the front and rear view of the frame is provided however the dimensions and shape depends on the type of Plastic Box you have.

The Trap Door Chamber can be seen in the pencil diagram.

2. Chamber Door

A picture of the Chamber Door can be seen which is built into a cut out of the front of the Plastic box. The door has a small handle so it can be easily opened from the front to remove items caught in the trap.

The Chamber Door is made from two layers of Styrene sandwiched and glued together with two pins used as hinges inserted into the frame of the door cavity. The dimensions once again are dependent on the exact size of the plastic box.

There are four holes in the front of the door with a very thin transparent styrene sheet over the top. This provides a window so you can view anything in the trap chamber.

Step 7: Build the Circuit Board

Picture of Build the Circuit Board

1. Mount Circuit Boards in Plastic case

It is best to work out the position of the circuit boards first and pre-mount the Vero board before starting soldering any components. This way when you complete the circuit you just drop it into the mounts and know it will fit.

In my case the main circuit board is mounted separately from the relay however this is not mandatory.

Cut the Vero board to size and drill mounting holes in both the Vero board and plastic case. Use plastic spaces on both sides of the Vero board to ensure the circuit side is not shorted out by the metal screws/nuts

2. Circuit Layout

The basic layout of the key IC and Transistors is provided however it is best to follow the circuit schematic and work through building the circuit on Vero as most people have their personal preference for layout.

I have chosen to mount the LEDs so they can be viewed externally for testing purposes however they can be just mounted on the Vero Board.

I also mounted the Relay on a separate board and mounting screws when developing the project however this was only for development purposes.

Step 8: Adjustment and Testing

Picture of Adjustment and Testing

1. Align Trap Door before powering on

With the power off make sure the trap door is flush with the top of the case. If this is not the flush then adjust the length of the coupling by turning the rod thread in the aileron. Check that the trap door swings from open to closed with minimal friction. Make the necessary case adjustments if required.

2. First time powering on

When first powered on the Trap Door should close and then reset once. The LEDs indicate the status of each stage of the circuit.

D5 will light if there is something obstructing the infrared beam to the sensors

D6 will stay on as long as the trap door is closed

D7 will disable any further triggers to the trap for a time out period until the trap has reset

These LEDs are useful to troubleshoot any issues with first setting up the fly trap. Various test points and voltage wave forms are described on the pencil circuit diagram.

3. Sensitivity adjustment

There is one adjustment for setting the sensitivity of the infrared detection of objects. The best way to do this is as follows

(i) Place the unit in ambient light (not direct sunlight) and power on the unit.

(ii) When the trap has reset adjust RV1 slowly until the trap sets off.

(iii) Back off the adjustment by 25% and then test the unit again.

4. Final Testing

As in the demonstration video, small objects should be able to be tossed into the jaws of the Fly Trap and it will capture them. Note that there is a time out between resets of the trap, so if D7 is lit then the trap is not ready for its next victim.

Have fun!!

PS. we have successfully caught flies and other unfortunate insects in this unit and it could be developed further for this purpose if need be. Experimentation with bait, colour of the Trap Door and lighting are all considerations if you feel compelled to do this.


countrywill (author)2015-08-01

Hi is there a PCB board available for this



Unfortunately not however you can easily used Vero board to construct the circuit from the diagram in step 7.

allguard (author)2015-04-07

How much weight will the door support?

TechKiwiGadgets (author)allguard2015-04-07

it was designed for very light objects however a small marble can roll over it and the door remains flat. The solenoid spring determines how much weight could be held.

clint1122 (author)2014-09-23

hello sir. i just want to ask if there is something better picture quality of the circuit?

Hi try this

Hi sure no problems. I'll tidy up and send through and put up a circuit diagram.

Thanks a lot sir. :)

BryanD1 (author)2014-08-18


TechKiwiGadgets (author)BryanD12014-08-18

Thanks :)

rimar2000 (author)2014-07-26

Clever idea!

Thanks. I should really have used a modern micro based circuit and 3d printed some components however you do what you can with what you have. Using retro electronic components probably makes this an antique :)

electronics?!? i'm still using sticks and rocks!

srilyk (author)fixfireleo2014-08-03

Sticks and rocks?! I'm still using a real venus flytrap!

DDW_OR (author)TechKiwiGadgets2014-07-29




Sweet and


I love retro technology, I think the people undervalue the dark side of advanced technology. When all steampunk people are dead, nobody will know how to cut a piece of wood using a manual saw.

I agree :) retro tech is great

joedix (author)2014-07-29

Perhaps adding Sticky paper in bottom of tray, to "lock" them down, as other insects (spiders) may also get caught investigating the allure of a free lunch.

However, Great write up.

dnaman (author)joedix2014-07-29

Or .... just leave it as it is but put a few (hungry) spiders in the bottom tray.

TechKiwiGadgets (author)dnaman2014-07-29

ha ha i like this idea

dnaman (author)TechKiwiGadgets2014-07-29

I wonder how it would appear to the spider ....

There you are, sitting in the dark, maybe having a little doze. Suddenly there's this flash of light and dinner drops in your lap (do spiders have laps?).

If I were a spider I could get quite philosophical over that .... existence of God, heaven etc.

jaxboy (author)dnaman2014-07-31

To quote Larry the Cable Guy, "Now that's funny, I don't care who you are!

TechKiwiGadgets (author)dnaman2014-07-29

Sort of like "The C18 Locker Aliens" in Men in Black :)

Silence (author)2014-07-30

Nice ! does it catch flies ?

TechKiwiGadgets (author)Silence2014-07-30

Yes definitely works. If you can lure them into the jaws they set off the trap :)

Silence (author)TechKiwiGadgets2014-07-30

Bloody brilliant !
Try adding various baits and see what works best... need to make sure they get caught and can't get back out when it resets though. Then get a pet that eats flies...

TechKiwiGadgets (author)Silence2014-07-30

Thanks for the feedback :)

awagner18 (author)2014-07-30

Where is the video did I miss it

its the second image in the instructable. Doesnt seem to show up on mobile app so try a desktop or tablet :)

Modellights (author)2014-07-29

First some other general ideas. For lots of small fruit flies or similar, the $5 electric bug racket from HF is hard to beat. Just wait until near dusk, turn off the lights and close the blinds on all but a couple windows, and then just get them there easily. Even if something was left out and there are a lot over a house, you can get rid of most of them the first evening without much effort.

Some variations might be worth trying:

A UV LED, for attracting insects.

Charging a photoflash cap for a little bit of electrocution action once it's caught.

Instead of a solenoid, could use a servo and spring setup. Use a round servo wheel and cut it to a spiral cam. Spiral the door to open, then on detection bump it past and the spring snaps it shut.

Thanks for the feedback. Great ideas :)

seth42 (author)2014-07-29

This is really cool! The only problem is that i am new to arduino.

Jobar007 (author)seth422014-07-29

That's OK because this doesn't use Arduino. You could certainly program one to perform this function with fewer components though.

seth42 (author)Jobar0072014-07-29

Good to know thanks. Told you I was knew to arduino:)

tmaragakis (author)Jobar0072014-07-29


GigglingHam (author)2014-07-27

TechKiwi I have a question is there a potential to add something to the trap to attract bugs like pheromones or something?

definitely. I’ve had suggestions about the colour of the trap door as well. I
think it’s a combination of things worth trying.

Actually, if it's about getting flies out of the house (house flies not fruit flies) if you could rig a light in there and then place it in a dark room, it would work without pheromones. Next time you have a fly in your house bugging you (pun intended) wait until night, turn a light on in the bathroom and lights off everywhere else. Soon it will be in the bathroom, attracted to the light. Use that against them by putting a light inside the trapping mechanism of this contraption.

srhnz (author)Bannockburn2014-07-29

[Snip from]

A-region ultraviolet light attracts insects

Unlike humans, some species of flying insect such as houseflies and bluebottles, wasps and mosquitoes can see ultraviolet light. In the 365-nanometre range in particular it exerts an enormous attraction on these bugs. This fact has been put to use for almost 20 years in the indoor battle against injurious flying insects.


UV-A range is 320 nm to 400 nm, so something like would be ideal as a light based attractant (tech data sheet is also on the page)

Nice project..something to build in prep for a Kiwi summer :-)

srhnz (author)srhnz2014-07-29

And another thought..could integrate the circuit from a bug zapper racquet into the top flap to fry the little you end up with a collection of dead ones..not live ones. You won;t have to deal with slow learners then :-)

TechKiwiGadgets (author)srhnz2014-07-29

lol :)

yep lighting definitely is a factor and ideas along this line worth trying. Thanks for the feedback :)

fixfireleo (author)2014-07-29

awesome! just rub some raw chicken juice all over the door as bait!!! will work best after a couple days.

acoleman3 (author)2014-07-29

so.....what do you use as bait. the plant uses sweet smelling sap.

Mark Rehorst (author)2014-07-29

like this, and it's good, but I think I'd like it more if it actually squished the fly then dropped its filthy, no-good, disease-ridden carcass into the drawer. THAT would be great!

Verticees (author)2014-07-28

Great project, I have to make this. Thanks for sharing!

Thanks. Let me know if you have any questions on dimensions etc

About This Instructable




Bio: Crazy about technology and the possibilities it can bring. I love the challenge of building unique things. My goal is to make technology fun, relevant ... More »
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