This project came about after a recent invasion of mice in my garage. Mice around my way are way too clever to risk any obvious traps.
This calls on the need to innovate to eradicate, technology to the rescue!
Here's my design goals:
* Keep the design simple and low cost by using off-the-shelf modular components. Just wire and assemble. No arduinos required
* Use a simple gravity assisted, low trigger force, box trap mechanism
* Operate from a single USB rechargeable 18650 Lithium Ion battery. Less batteries in landfill.
* Low power consumption for a long battery life
* No contact, PIR triggered mechanism.
* Keep it pet and child friendly
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Step 1: Design
The physical trap mechanism comprises of an upside-down plastic container, tilted on one edge. The opposite raised edge is supported by wooden balsa stick (lollipop/waxing type)
The PIR sensor is located under the baited container. When the PIR detects movement under the container, it actuates a solenoid which pushes the supporting stick. This causes the container to fall and trap the mouse.
For the PIR sensor I chose the SR505 module. The SR505 can operate reliably at a voltage above 4v. To lower the operating voltage, even further so that I could use it with a single lithium battery, i bypassed he SR505s internal polarity protection diode.
To prevent unnecessary power consumption after the container has fallen and trapped the mouse, a mercury tilt switch is added. In the dropped box state, this cuts off power entirely, conserving battery life for the next manual trap setup. This also prevents keeping the solenoid energised unnecessarily for long durations which can cause the coil to heat up and burn out.
A switch for live and test modes is added to ease setup. In Test mode, PIR activity lights up an LED. In Live mode, PIR activity actuates the push solenoid.
The average power consumption for the SR505 is 50uA. With a 1000mAh battery it should give a theoretical 20,000 hours. I think it should easily last a month with several triggers each week, lets see.
The actuator solenoid draws 0.8amps at 4v, so is switched by another relay module. Its difficult to find an of-the-shelf mosfet module which will switch the solenoid actuator direct at such a low voltage and high current. Thie relay module also helps keeps the design simple, at the cost of two solenoid coils.One for the low power relay side (30mA), and the other for the:solenoid actuator coil (800mA).
In the photos I originally made my own relay module using a bc109/6v relay/reverse bias diode setup. This was before the ready made module finally arrived from China.
To reduce standby power wastage by the relay module, the onboard power LED is desoldered.
The circuit is pretty simple to understand, and easy to wireup and troubleshoot due to its modular components.
To reduce the pir sensitivity and trigger zone, a hood is added around the pir sensor..
To prevent trapped rodents from lifting the container box, a lead sheet was added to the roof, to weigh it down.
Step 2: Parts
* Large Plastic Container box, either square or rectangular, ideally transparent.
* Weight on top of box, eg tack a book. I used some scrap lead sheet I had.
* Solenoid 3v-6v (push and pull actuator type). This project uses the push actuator side.
* 18650 batt or recycle from an old laptop battery.
* USB charger module
* PIR SR505 module
* 5v active high relay module
* SPDT mode switch
* Red led
* Small enclosure box to house electronics and protect components from rodent attack.
* 2 balsa wood lolipop/waxing sticks
Hot glue gun
Step 3: Assembly
Solder as per wiring diiagram.
Cut, drill, glue components as pictured.
Ensure solenoid is positioned so that the solenoid push actuator has maximum travel length by positioning it flush with outer container box surface, when in the retracted position.
Hot glue a narrow plastic ledge (3mm width) for the supporting stick to be propped up against. This should be a smooth friction free surface.
Step 4: Trap Setup
During initial setup it's switched to TEST mode.Once the PIR is stabilised (red led off) it is switched to LIVE mode. In TEST mode, the red led indicates a trigger activation. In LIVE mode the solenoid actuator operates instead.
Place bait under container.
Support raised edge of container with stick touching solenoid actuator.
Wait for LED to stabilise to OFF.
Switch to LIVE mode.
Trap is Set.
Whilst tinkering with the design, I caught 8 mice over the period of a month , and all on single charge.
The tell tale signs of a week battery are that the PIR takes longer to stabilise in TEST,mode, about a minute. On a fresh charge it stabilises much quicker.
Checking is easy, just look for a dropped down level container box. I have had very few false triggers.
Step 5: Eradicate!
Some tips on eradication.
Firstly, close of all entry exit points. This can be much harder if its not obvious. If you dont do this you will be fighting a losing battle. Revisit all closed off points as they will persist to break through. Thin tin can metal works best as it can be cut to shape with tin snips and nailed in place.
Keep any food sources/grain/seeds in closed containers.
The box needs to be weighted as the trap is relatively light. Otherwise they will escape by dragging/jumping/levering or even external assistance from fellow rodents.
Don't put the trap box on a separate platform, keep it border free on the surrounding floor/base. Mice are wary of stepping into an obvious baited zone, they will remember and communicate, and will avoid. Keep the trap box raised on the existing surrounding floor/base, as they feel they are safe on common ground. This makes moving trapped mice a little tricky, but is the key to its success.
Camouflage the trap by keeping it adjacent to existing tall containers, bottles boxes etc. Keeping it in a dark place makes it less obvious and gives them a sense of security.
Dish out a free bait sample along a rat-run away from the trap. This lets you know you still have guests, and also entices them for more under the trap.
Move the trap location after a few days of non capture. I thought the mice would wise up, but the open platform floor design seems to work.
Keep a hard card (eg backing from an A4 file) for sliding under box to remove the trapped pest.
There are two schools of thought on what to do with the trapped rodent, exterminate or release? I'm not one to advocate either method. The good karma option is to release it back into the wild. I'm sure they serve some ecological purpose, like curbing the human population by spreading the plague?. Ok, just not in my garage please :-)
Step 6: And the Name.. RIBO ?
Every good project needs a name!
As the box I used was a recycled HARIBO sweet box, I thought I would base the name on it. To avoid infringing any trademarks, I cut it short to RIBO.
This project has been fun to design and has served its purpose welll. I'm also armed for any future invasions. Hopefully this heelp others and be of educational use.
Participated in the